32ND INTERNATIONAL SYMPOSIUM ON BALLISTICS
32nd International Symposium on Ballistics
MACHINE LEARNING AND NUMERICAL INVESTIGATION ON DRAG REDUCTION OF UNDERWATER SERIAL MULTI-PROJECTILES
The quest to achieve high launching frequency and higher speed is one of the key goals for researchers in the field of underwater projectiles. Many methods have been proposed for reducing the drag force to reach higher speed, such as superhydrophobic surface, compliant surface, and so on. One of the most effective methods is supercavitating drag reduction technology, which can be used to achieve a significant reduction of hydrodynamic drag by wrapping a large, continuous cavity around the underwater projectile. To increase launching frequency and decrease drag force of underwater projectiles, a serial multi-projectiles structure based on the principle of supercavitation is proposed in this paper. However, the matching relationships of serial multiprojectiles between different conditions (cavitation number, distance between projectiles, etc.) and the drag characteristics have not been investigated, because obtaining the relationship between drag characteristics and different conditions requires simulation time and extensive calculations. In this paper, computational fluid dynamics (CFD) method and machine learning method were coupled to investigate the natural supercavitation phenomenon of the serial projectiles to reduce the computational cost and improve the simulation accuracy. Firstly, the numerical simulation model for the underwater supercavitating projectile is established and verified by experimental data. Then the evolution of the supercavitation for the serial multi-projectiles is described. In addition, the effects of different cavitation numbers and different distances between projectiles are investigated to demonstrate the supercavitation and drag reduction performance. Finally, the artificial neural network (ANN) model is established to predict the evolution of drag coefficient based on the data obtained by CFD. The results predicted by ANN are in good agreement with the data obtained by CFD. The findings provide helpful guidance for the research on the drag reduction characteristics of underwater serial projectiles. The main conclusions of the study are as follows: (1) The cavity will develop, fuse and collapse in the water and natural supercavitation phenomenon is observed when underwater serial projectiles move at a high speed. The serial multi-projectile structure can reduce the drag of the second projectile and achieve the goal of drag reduction. (2) The length and aspect ratio of supercavity around serial projectiles decrease with the decreasing of the cavitation number, and the drag coefficient of the second projectile decreases. The length and aspect ratio of supercavity decrease with the 3 decreasing of the distance between serial projectiles, and the drag coefficient of the second projectile decreases. (3) The drag coefficient of the second projectile predicted from the ANN model has a high accuracy, where the regression R2 values of training, validation, and testing samples are above 0.99. Machine learning has an obvious advantage in simplifying computational complexity and increasing computational efficiency. Furthermore, the discussion of different cases is based on static projectiles. However, in real-world applications, the movement of serial projectiles should be considered. This is the future direction for this work.
INVESTIGATION ON SHOCK-INDUCED REACTION CHARACTERISTICS OF Ti/PTFE ENERGETIC MATERIAL
In recent years, titanium/fluoropolymer composites have become a new type of energetic structural material, which can release energy under high-speed impact. In this study ï¼Œ Ti/PTFE energetic material was fabricated: mixing by ball milling, molding under 20MPa pressure, sintering at high temperature, and analyzing the micro-morphology of Ti/PTFE energetic material under SEM. And through SHPB impact compression test, the mechanical properties of Ti/PTFE energetic materials under a high strain rate (1*103- 3*103) at room temperature was analyzed. Furthermore, the impact-induced reactivity of Ti/PTFE energetic materials was investigated through a quasi-sealed chamber test. It shows that the exothermic chemical reaction is more intense with the increase of impact velocity.
SERIAL NUMBER RECOVERY TECHNIQUES ON STEEL PLATES; FRY’S REAGENT AND EDDY CURRENT TECHNOLOGY
The recovery of obliterated serial numbers is a common process involved in the forensic analysis of firearms confiscated in criminal cases. The current standard method of recovery involves the use of chemical reagents which are highly destructive to the material. The destructive process does not allow subsequent analysis, nor does the test always recover the serial number completely. A new technology that utilizes eddy currents and magnetic fields to recover serial numbers without the use of chemicals has been proposed to allow for an almost non-destructive recovery. This research has shown that the use of eddy currents and magnetic fields is a promising technique for obliterated serial number recovery and that further research may indicate it is a suitable replacement for the currently used Fry’s Reagent.
NUMERICAL SIMULATION STUDIES ON THE EFFECT OF CHARGE STRUCTURE ON DETONATION DRIVING CHARACTERISTICS OF WHIRLING FRAGMENTS
To attach against clustered low-protection UAVs, this paper proposes a new type of whirling fragment structure and warhead arrangement. The non-linear dynamics software Autodyn was used to carry out a numerical simulation. The detonation drive of whirling fragments by different cavity diameter charges was analyzed. The research results show that as the cavity diameter increases, the pressure peak on the outside of the shell will increase first and then decrease, the detonation wave action time will gradually decrease, and the output of the detonation wave at the end of the detonation action will be smoother; The detonation driving process of the whirling fragment is divided into two stages. The first stage is the sharp acceleration process of the detonation product during the action of the detonation wave; the second stage is the scattering process accompanied by spin motion after the fragment leaves the shell. As the diameter of the cavity increases, the center-of-mass velocity of the whirling fragment decreases; there will be a velocity difference between the head and the tail of the fragment then the velocity will be exchanged. The velocity difference first increases and then decreases with increasing cavity diameter; an increase in the cavity diameter will cause a periodic change in the whirling fragments' rotation, which first decreases and then increases.
A REVIEW OF FUTURE TRENDS IN 3-D PRINTING OF ARMAMENT AND EXPLOSIVE DEVICES
Advances in Computer aided design (CAD), modeling and Three-dimensional (3D) printing has led to paradigm shift in development of innovative and miniaturized explosive devices for armament applications. In conventional techniques, explosives are either pressed or casted and machined to required geometry. These conventional processes are mostly manual and monotonous; require high-cost tooling and the lead-time from concept to product is high. 3D printing is an automated additive manufacturing process in which the material is deposited layer-by-layer to build physical part with any intricate geometry and profile, from the CAD model of the part. 3D printing of explosive devices offers advantages of computer aided design techniques, automation, direct physical part fabrication, low lead-time, low cost and any geometrical shape can be printed. It also offers advantage of printing explosive parts in the battlefields. In this paper, along with the detailed review of future trends in 3D printing of armament and explosive devices, a case study of 3D printing of plastic bullets in Acrylonitrile Butadiene Styrene (ABS) material is presented. The plastic bullets are used in low intensity conflicts and riot control. The experimental firing trials were conducted using standard AK- 47 gun firing on Gelatin target blocks placed at 30 m distance from the muzzle of the gun. The trials showed performance of ABS bullets in terms of lethality and velocity drop comparable to existing plastic bullets made of Nylon-66 manufactured by injection molding process. 3D printed ABS bullets have advantage of batch-to-batch repeatability, high accuracy. 3D printing is revolutionizing the way armament and explosive devices are manufactured, performance improvement and miniaturization.
ELECTROMAGNETIC RAIL GUN FRAGMENT ACCELERATOR CONCEPT DEMONSTRATOR
The future objective of this study is to establish testing techniques to evaluate the penetrating ability of shrapnel fragments produced from fragmenting warheads. Difficult to capture data points such as residual velocity and mass are required to, individually, characterise single fragment penetrability. One of the more challenging aspects of penetrability testing is the ability to study individual fragment impact at speeds exceeding 2 km/s. Fragment acceleration by means of an electromagnetic (EM) rail gun seems to be well suited to test weapon applications and is expected to be the future system of choice for high velocity fragment impact analysis. A concept-demonstrator rail gun (6000J, Ma MV 320 m/s) and internal ballistic model is presented in this study establishing technology toward the future development of a full-scale EM fragment accelerator test system. This paper presents the findings and challenges encountered during the development and testing of small-scale electromagnetic rail gun. In particular, findings are presented onunexpectedforward plasma escape likely resulting from excessive joule heating in the armature-railinjection region.
LABORATORY SIMULATION OF UNDERWATER BLAST WAVES BY HIGH SPEED WATER ENTRY
A method is presented for simulating underwater blast waves for unconfined laboratory experiments. High speed water entry of projectiles can create ballistic waves that resemble underwater blast waves. This paper provides several practical examples of launching projectiles downward into a 1000L container of water, a method accessible in many laboratories. Resulting ballistic waves are measured with a piezoelectric pressure transducer. Results are reported for four projectiles: 1) A 4.5 mm diameter steel sphere fired from a pump “bb gunâ€ impacting at 199 m/s. 2) A 7.82 mm diameter hardened lead sphere fired from a 30/30 rifle impacting at 345 m/s. 3) A 5.59 mm diameter lead hollow point bullet fired from a .22 LR rifle impacting at 389 m/s. 4) A 9 mm diameter jacketed hollow point pistol bullet fired from a service caliber pistol impacting at 397 m/s. In all cases presented here, the ballistic waves generated in high speed water entry might find experimental use as simulated underwater blast waves, depending on experimental requirements. Peak blast magnitude ranged from 400 kPa to 2500 kPa, and positive pulse duration ranged from 0.2 ms to 0.6 ms. Wave shape varied in quality. Â
DEVELOPMENT OF HIGH SPEED PHOTOGRAPHY TECHNIQUE FOR UNDEX APPLICATIONS
This paper describes recent experimental development of high speed photography (HSP) applied to UNDer water Explosive (UNDEX) trials. The imaging technique adopted used overhead mirrors and a Perspex® plate on the surface of the water in a tank holding 11,000 litres of water. The HSP has identified the shock wave velocity, shape and timescales and the bubble dynamics as well as the interaction with the target (i.e. Glass reinforced panel (GFRP) composite panel). Charge sizes ranged from 40-140g of PE4 explosive and good images were obtained of the target response. Improvements to the technique will be higher fidelity to enable Digital Image Correlation (DIC) measurements for the panel as well as improved target fixings to prevent lateral motion so that damage could be induced in the panel. The technique can also be used on bigger scale UNDEX trials.
FUNDAMENTALS OF PROPERTY PREDICTION OF COMPOSITE ENERGETIC MATERIALS
In the field of energetic materials, the mixing or blending of various material components into a composite material with certain desired properties is common practice. The compound properties are often not verified experimentally and one has to rely on composite properties derived from so-called property mixing rules. In this study we evaluate these composite properties in relation to details of the pure components. A brief overview of mixing rules, as proposed by Dobratz, Bruggeman, and Poon and Shin, is given. These commonly used mixing rules are applied on different propellant simulants, tetryl and TNT in order to predict the relative permittivity (or dielectric constant). These predictions are discussed and, subsequently, compared to experimental observations.
TNT EQUIVALENCE, BERTHELOT THEORY AND THE TRAUZL LEAD BLOCK TEST
An experimental measure of explosive performance is the Trauzl Lead Block Test. This paper assesses Trauzl, examining results against detonation parameters, including TNT Equivalence (TNTe) and Berthelot theory, attempting to find correlations. Power Index is shown to fit Trauzl, with a linear correlation, zero intercept and a near unity gradient, with an error of 4%. Trauzl is shown to be a good measure of the effectiveness of Explosive Power (EP). The Heat of Detonation (Q) and TNTe Q have a weak correlation with the Trauzl. Berthelot theory is simplified, becoming a product of Heat of Detonation and Volume of gases, nearly identical to Power Index. Berthelot is shown as related to Explosive Power (EP). Without correction, Berthelot is not recommended, since the gradient with Trauzl is 10% high and theoretical comparison with TNT is 12% high. Berthelot and Power Index have linear correlations with Trauzl, with an identical Goodness of Fit.
NUMERICAL SIMULATION ON THE VELOCITY DISTRIBUTION FOR DOUBLE-LAYERED PREFORMED FRAGMENTS BY EXPLOSION
As one of the most commonly used conventional ammunition in the military field, the double-layered preformed fragment warhead can achieve maximized damage efficiency against multiple types of targets within large coverage. In this paper, four different arrangement types of the double-layered fragments cylindrical casing filled with explosive charge were discussed. Numerical simulation were conducted to calculate the flight velocity and flight angle of all the fragments using the dynamic 3D software ANSYS/LS-DYNA. Based on the simulation results, the effects of the fragment layer on the distribution of the fragment velocity were analyzed by comparing different types of double-layered preformed fragments cylindrical casing. Furthermore, the detailed process such as the propagation of detonation wave, the collision of fragments between different layer, were studied to reveal the difference of the distribution of the drop point with different initial arrangement for double-layered fragments. Further research involving with different radius and material of fragments were conducted to figure out the critical parameter in warhead design. Finally, the statistics on energy utilization of four different double-layered preformed fragments showed the phenomenon of the leak of detonation product between fragments can affect the terminal velocity distribution.
NUMERICAL ESTIMATION OF VARIATION OF BLAST PRESSURE AND TEMPERATURE OF BLAST WAVE WITH TIME DUE TO DETONATION OF TNT IN AIR
High explosives on detonation generate high pressure shock waves moving initially at very high velocities in the ambient medium and damage the encountered targets. The expanding hot gases in blast waves are also responsible for the damage. The extent of damage to a target depends on the magnitude of pressure and impulse of the blast wave, and temperature due to explosion. A theoretical analysis is carried out to predict the pressure and temperature produced in the expanding blast as function of time by solving analytically the governing equations. The initial peak pressure and temperature of blast wave, which are required in the theoretical analysis, were calculated making use of the blast wave theory. Results obtained for blast pressures at different distances using this theory were published by the authors earlier. The same numerical analysis is used for obtaining variation of pressure and temperature with time and presented in this paper. The high explosive used in the experiments is TNT of varied weights.
FORMING CHARACTERISTICS AND DISPERSION PATTERN OF NON-AXISYMMETRIC MEFP WITH Ta-2.5W Liner
For the purpose of directional damage effects, two MEFP warhead schemes with non-axisymmetric charge structure were designed. The liners were made of Ta-2.5W alloy, and multi-points initiation method was adopted. By LS-DYNA hydrocode, the forming characteristics of directional MEFP was studied and the dispersion pattern of EFPs was obtained. With bigger dispersion angles both in the vertical and horizontal directions, one of the design schemes was chosen to test in experiment. The dispersion pattern obtained in experiment of the MEFP was consistent with the numerical simulation results, which validated the rationality of the design scheme and the numerical model. The MEFP with non-axisymmetric charge structure could be used for the directional damage purpose with higher penetration ability when compared fragment warhead.
A NEW METHOD TO IMPROVE THE FORMING PERFORMANCE OF EFP WITH FINS BY GROOVING ON THE LINER
In order to solve the flight instability of Explosively Formed Projectile caused by irregular fins, different design schemes are carried out to test the forming performance of EFPs with fins. Grid target and laser high speed photography were used to capture the forming characteristics of EFP in experiment. Both liners with the structure of two combined arcs and the liner with the structure of combined arc and cone could form EFPs with fins. But the EFPs were with irregular fins and were accomplished with big angles of attack and a necking tendency. With a bigger tail, the liner with structure of two combined arcs is much better than the structure of combined arc and cone in the view of flight stability. Then a new method- grooving on the liner is put forward to obtain EFPs with regular fins. Typical grooving parameters such as grooving position and shape are chosen to obtain an optimal EFP with fins. It turns out that by grooving on the liner, it is feasible to acquire a rodshape EFP with regular fins which could meet the design requirements.
ANALYSIS OF ELECTROMAGNETIC RADIATION PROCESS OF TYPICAL SINGLE-COMPOUND EXPLOSIVE
Explosion will generate electromagnetic radiation, the time domain waveform and spectrum generated from different types of explosives are different. For researching the characteristics of the electromagnetic radiation in process of explosion, the electromagnetic radiation signals and the images of the explosion process of typical single-compound explosives TNT and RDX are measured by wide band electromagnetic radiation signal measuring devices and high-speed photography. The experimental results show that the peak time of electromagnetic signals of TNT and RDX are significantly delayed compared with the initiation time of the detonation. The delay time of the peak signal of TNT explosion electromagnetic radiation is 55.07μs, and the delay time of RDX is 68.40μs. At 5m from the detonation center, the peak signal electric field strength of TNT and RDX explosion electromagnetic radiation is 1.92V/m. After the initial discharge interference signals have been removed, the electromagnetic pulse signals are analyzed by Fast Fourier Transform, it is shown that during explosion, the frequency of electromagnetic radiation is within 100MHz, and the frequency spectrums of electromagnetic radiation signals of different explosives are different.
COMPUTER SIMULATION OF BLUNT PROJECTILE IMPACT ON EXPLOSIVE CHARGE
Four of the standard insensitive munition tests involve the impact of various projectiles on the tested munition. Experimental tests are often conducted to obtain data on the critical impact velocity of different geometries of projectiles made of different material against explosive charges, either bare or covered with various inert material plates. The current study involved computer simulation with the IMPETUS Afea Solver® finite element analysis (FEA) of the impact of a brass blunt brass projectile on a bare Composition B explosive charge as well as charges covered with 1 mm thick steel, 3 mm thick aluminum or 5 mm HPDE (High Density PolyEthylene). The results were compared with those from experimental tests and simulations from other scientists. Simulations results were within 5% of the experimental results.
COMPARATIVE ANALYSIS OF LINEAR SHAPED CHARGE JET FORMING AND PENETRATION IN DIFFERENT MEDIUMS
In order to compare the forming and penetration process of linear shaped charge jet in three different mediums ( in the air/ under water/ under water with air standoff), threedimensional numerical simulation models were established using ANSYS / LS-DYNA software. The forming process and penetration performance of linear shaped charge jets are compared and analyzed. Simulation results show that the jet forming performance in the air is better and the jet head velocity is much higher compared with the under-water condition. By adding a hollow tank in front of the metal liner, the jet forming performance under water can be improved significantly. After 60μs of the detonation, the head velocity of three jets are 2750 m/s, 890 m/s and 2600 m/s , and the maximum penetration depths are 0.734DCã€0.092DC, 0.91DC respectively.
WAVE FRONT CAPTURING USING DETONATION SHOCK DYNAMICS
High fidelity fluid dynamics based combustion models for reactive media can be implemented by way of simulations but require significantly large CPU effort. The Detonation Shock Dynamics (DSD) models offer a simpler alternative. The challenge presented while implementing DSD equations is mostly computational. Accuracy, simulation time and spatial resolution considerations turn out to counteract each other and a tradeoff is necessitated. We present simulation results obtained for a single detonation point using the level set method for DSD and describe an example of such a trade-off. We demonstrate that curvature dependence and independence of detonation velocity affects this trade-off. We then address the hydro-code results using a test case with five detonation points. The times of arrival of the detonation front at certain locations (gauge points) are taken to represent the shape of the detonation front. Times of arrival obtained using hydro-code are compared with those obtained by the level set method which has been optimized for the three considerations above. The shape of the front gets similarly reproduced in both cases, but the level set method over predicts the time of arrival up to 10 percent. We conclude that more efficient computing hardware needs to employed for DSD simulations and the level set method would serve as a quicker means for preliminary checks of detonation point arrangements. We also suggest a method for accommodating time delays at detonation points. The initial scalar field is assumed to be a combination of Gaussian functions centered at the detonation points. This is taken to represent the detonation at certain lead time which is accommodated for in the algorithm. This lead time is reduced if any delay is to be accommodated. The above method for accommodating time delay has a limitation. The initial radius cannot be made smaller that the radius set by the standard decay constant of the initial Gaussian profiles of the scalar field. The accommodated delay cannot be longer than this radius divided by detonation speed to be employed. We offer a work-around involving a construction of suitably located secondary detonation points.
RESEARCH ON CRITICAL DETONATION VELOCITY OF INSENSITIVE EXPLOSIVE IMPACTED BY ROD-TYPE PROJECTILE
The numerical simulation on the initiation process of the covered insensitive explosive PBXN-109 impacted by tungsten rod-type armor piercing projectile was carried out by the shock physical explicit Eulerian dynamic software SPEED. The “up-downâ€ method was used to obtain the projectile critical detonation velocity. The effects of projectile diameter, projectile length, shell thickness and charge material on the projectile critical detonation velocity were obtained. The research results show that the projectile critical detonation velocity decreases as projectile diameter increases. It first decreases and then becomes stable as projectile length increases. It increases linearly as shell thickness increases. The critical detonation velocity of PBXN-109 charge is significantly greater than that of Comp-B charge. Affected by the charge initiation mechanism, the velocity amplification increases as projectile diameter increases, and the maximum value can reach about 154%. Utilizing the insensitive explosive PBXN-109 as the warhead charge can effectively protect against the impact initiation of rod-type projectile.
EXUDATION AND CRYSTAL GROWTH OF TNT IN MUNITIONS
For trinitrotoluene (TNT), exudation has been a recurring problem since the early 1920s. TNT exudate typically has an oily appearance and dries to a somewhat black color. Exudate, by itself, appears to be no more sensitive than TNT. However, if mixed with sand or grit, it can be very sensitive to impact or friction. Munitions which exhibit TNT exudate except where the design allows, should not be considered as safe and suitable for service. TNT exudate is formed due to the presence of impurities and the high temperatures that can be experienced in the service environment. Older TNT manufacturing methods leave significant impurities within the TNT, whereas more modern methods have improved the quality of the processed TNT, removing most but not all impurities. Another potential issue with exudation is crystal growth. There is some discussion within the munitions safety community that TNT crystals can grow within cavities of aged munitions. However, we believe that internal fill exudate and TNT crystal growth does not constitute a major concern for munition safety if standard munition handling practices are observed.
INFLUENCE OF FRICTION ON A DOUBLE CASED FRAGMENTING WARHEAD
The interface condition between the different casings in a multi-cased fragmentation charge is essential for its fragmentation behaviour. In this study, a double cased controlled fragmentation charge with a smooth outer casing and an internal grooved inner casing is considered. In particular, the influence on friction between the inner and outer casing on the fragmentation behaviour is studied using numerical simulations and experiments. In the numerical simulations, the friction coefficient in the contact between the inner and outer casings is varied. Experiments on charges with different interface treatments between the casings are performed with various diagnostic tools in order to capture the deformation, fragmentation and acceleration of the casings. Three different interface treatments that give rise to different friction coefficients are tested; a shrink-fit joint, a thin layer of lubricant grease between the casings and a Teflon layer on the outside of the inner casing. It is found that the amount of friction between the casings influences both the deformation before fragmentation and the resulting shape of the fragment from the outer casing. For the highfriction conditions, one large and several small fragments are produced for each diamond on the inner casing. The low-friction condition results in long zigzag-shaped stripes of materials originating from the casing material closest to the grooves and many small fragments from the casing material between the grooves.
TESTING A PRECISION INITIATION COUPLER BY DETONATION INDUCED CAVITY COLLAPSE METHOD
Precision Initiation Couplers (PIC) are used as a relay charge for initiating a shaped charge precisely along the liner axis. A PIC consists of an explosive column housed in an inert casing with suitable dimensions based on the detonation velocity of the explosive and shock velocity of the inert material. This paper explains a simple test method to qualitatively assess the performance of a PIC when it is eccentrically initiated. This method is based on the deformed shape of a plain cylindrical hole in an Aluminium block subjected to explosive loading. Symmetric collapse of the hole is observed when a PIC that is in contact with the metal block is detonated at a point away from the axis of the PIC. This test method can be used as a simple gonogo test for qualifying various designs of PICs.
EXPERIMENTAL STUDY ON W-Ni ALLOY FORMABILITY UNDER EXPLOSIVE LOADING
This paper presents an experimental study of the formability of W-Ni alloys with three different densities using the explosive loaded flyer plate method, so as to explore the highdensity alloy suitable for explosively formed projectile liner. The results showed that the tested materials all suffered different degrees of fracture failure and could not form a complete penetrator, which could not be used as a candidate material for the explosively formed projectile (EFP) liner. Based on the results, the forming performances of the tested materials were compared and analyzed. Combined with the material microstructure, the failure mechanism of W-Ni alloys was analyzed, and the feasibility of using W-Ni alloys as EFP liner materials was discussed. The forming performance of W-Ni alloys under the explosive loading condition was improved with a decrease in W content. Its microscopic mechanism lies in the increase of the matrix phase content, which enhances the coordination ability of dislocation movement to plastic deformation. The failure of W-Ni alloys is attributed to the difference in performance between the different phases of the multiphase alloy. When W is completely dissolved in the nickel-based ductile matrix, the W-Ni alloy is transformed from a multiphase material to a single-phase alloy (FCC), completely eliminating the dislocation pile-up problem due to the presence of the W phase. The singlephase structure may be necessary for the W-Ni alloy to be a candidate material for the EFP liner.
FLAMMABILITY ANALYSIS OF GAS CYLINDERS UNDER FIRING IN DIFFERENT ENVIRONMENTAL CONDITIONS
This paper presents the results of testing such materials with bullets: 7.62×54R LPS FMJ, 7.62×39 BZ, 7.62×54R B-32 API and 7.62x51T. For the study, 11 kg propanebutane gas cylinder was used with different gas content: 0.5 - 5 kg at ambient temperature 22°C. One to five shots were taken at each cylinder, and the heat flux and overpressure wave were estimated under various assumed storage and transport conditions. The impact of the bullets was recorded with a high-speed camera and thermal camera. This paper presents the temperature ranges, burning area spread areas and histograms due to the impact of various bullets on flammable gas cylinders. The excitation conditions for flammable gas cylinders to burn were determined.
NUMERICAL SIMULATIONS OF REACTIVE MATERIAL-TITANIUM JET PENETRATING MULTI-SPACED PLATES
The shaped charge with a reactive material-titanium liner (RM-TL) could not only meet the requirement of jet penetration depth, but also cause enormous aftereffect inside the target. Based on the platform of AUTODYN-2D code, the jet formation of the RM-TL shaped charge and its penetration behavior to multi-spaced plates were studied. Numerical simulations showed that the inner titanium liner mainly formed a high-velocity precursor jet and the outer reactive material liner became a major part of the slug during the jet formation process. With increasing the reactive liner thickness, the composite jet tip velocity dropped off gradually, and the pressure and the temperature in the reactive liner during detonation also decreased. For a given penetration time, with the increase of the reactive liner thickness and the cone angle, the penetration capability of the composite jet into multi-spaced plates reduced, but the mass of reactive materials inside spaced aluminum plates increased significantly. With increasing the titanium liner thickness, the penetration depth first increased and then decreased, but the penetration hole-diameter of multi-spaced plates and the follow-thru reactive materials inside the target dropped off, and most of the reactive materials accumulate in the hole of the steel block.
INNOVATIVE MESHLESS APPROACH FOR SHAPED CHARGES MODELLING VS EXPLOSIVE REACTIVE ARMOR
We focus on shaped charges modeling. Combining large deformations, numerous interface productions and strong damages mechanism, those events are numerically challenging. Eulerian finite element methods are classically used. However, they induce very long computation times, accuracy losses and need opening criteria to deal with failure. Among the Lagrangian approaches the meshless methods called Smoothed Particle Hydrodynamics appears as a relevant alternative to prevent such shortcomings. We propose to use an alternative scheme called -SPH-ALE. Based on the ALE framework, it achieves robust and consistent stabilization through an arbitrary description of motion. Its implementation on a Viper shaped charge shows that the scheme handles the jet generation process as well as its resulting interaction with an ERA target. Both stability and accuracy are increased with respect to classical approaches. Also, taking advantage of GPU computing, such results are achieved in reduced computation times with respect to classical CPU implementations.
BLAST PEAK OVERPRESSURE DETERMINATION AND VALIDATION AT VARYING ALTITUDES FOR SPECIAL AMMUNITION TO TRIGGER SNOW AVALANCHE ARTIFICIALLY
There has been development, deployment and exploitation of various systems to trigger snow avalanche artificially and minimize the chance of occurrence of snow avalanche in an unpredicted manner. Few of these are based on the usage of explosives to generate adequate blast Peak Over Pressure (POP) above the fracture zone in the pre-surveyed and identified avalanche prone areas. In an ongoing study on development of a special class of high explosive ammunition for being fired with 84mm Recoilless Weapon System, the need to evaluate the quantum of blast POP has been understood. In the presented study, the tentative configuration of the projectile, the nature and quantity of explosive and the resulting terminal performance have been discussed. Numerical simulations and well-established formulations have been used to predict the levels of blast POP generation due to the ammunition and the outcomes have been compared. The work has been extended to validation of the generated outcomes with the data obtained by conducting static experimentation with the high explosive filled prototypes and measuring the blast POP at mean sea level as well as at high altitude.
EXPERIMENTAL INVESTIGATION OF IMPULSE IN A VENTED SMALL-SCALE BUILDING SUBMITTED TO AN INTERNAL DETONATION
This work introduces a dedicated small-scale experiment aiming to investigate the pressure and impulse in a vented volume submitted to an internal detonation. A cylindrical highexplosive charge detonates into a building vented by four openings. Various experimental diagnostics were used in order to directly measure or indirectly estimate the internal impulse. Thus, the reflected pressure on the side walls were recorded, as well as the acceleration, velocity and elevation of the mobile roof thanks to different means. A mechanism similar to a blowpipe was also tested: the internal pressure accelerates the projectile and a PDV probe registers its velocity. The overall agreement between all the diagnostics is rather good, but some of them appear to be unsuitable while others need further analysis or improve. The experimental set-up and some of the associated diagnostics appear to be quite appropriate for further investigation on the effects of metallic casing and fragment-induced concrete dust on internal pressure and impulse in a vented building.
UNDERWATER MINE EXPLOSION AND ITS IMPACT ON THE TARGET SHIP
Underwater mines are one of the major threats to surface ships and submarines. In the present work, detection, localization, and the shock loadings on a target ship due to explosion caused by an underwater multi-influence bottom mine containing most advanced PBX-charge have been studied. It was found that the keel shock factor (KSF) value is 0.50 kg1/2m-1 up to the water depth of 70 m. The shock wave energy at 70 m water depth is 14.8 kJm-2 where KSF equals to 0.50 kg1/2m-1. For a target ship, a significant drop in the blast pressure wave value (8.5-3.4 MPa) between the stern to the bow is noticeable with the total duration of shock loading of 0.0362s. The method proposed in the present study could be used for quick and reasonably accurate estimation of the impact of an incident shock wave underwater on the target ship.
In the STANAG 4569, AEP-55, Volume 2, a NATO standardization agreement defining the protection levels for the occupants of logistic and light armored vehicles, the testing conditions for underbelly improvised explosive devices (IEDs) are specified. This document regulates that for the loading tests, the underbelly threat has to be buried in water-saturated sandy gravel. However, the use of sandy gravel has some drawbacks, for instance reproducibility, time consumption, and cost. This paper focuses on the investigation of alternatives to sandy gravel, which could produce similar specific and cumulative impulses. The impulses are measured with a ring technology developed at the Fraunhofer EMI. These experimental results can be used to develop new test conditions at original scale that are more reproducible, easier to handle and cheaper than the actual tests made with STANAG sandy gravel.
MEASUREMENT OF DYNAMIC RESPONSE OF SS316 UNDER HIGH STRAIN RATE LOADING
The paper discusses the experimental methods and techniques to measure the dynamic response of austenitic stainless steel SS316 subjected to the intense shock load of high explosive. The strains experienced by the material are transient in nature and last for a fraction of second with peak strain value of 15%. For experimentation, the cylindrical structures of austenitic stainless steel SS316 in various diameter 200mm-400mm, height 200mm-800mm & thickness 1-1.2mm were arranged by IGCAR . These cylinders were filled with water and rigidly held from both ends in a counter weight foundation. The experiments were conducted by detonating the explosive charge at the center of these water filled cylinders. The quantity of explosive used in trials varies from 4grams to 50grams. The response of the cylindrical structure under intense load of high explosive charge was measured by using post yield strain gages having strain limit of 15 %. The TML make post yield strain gauges model No.YFLA-10 were pasted on the cylinder in axial and shear directions to measure the dynamic axial and hoop strains. The strain gauges used were made of constantan material having 120Ω resistance, 10mm length and gauge factor of 2.1. These gauges were pasted on the cylindrical structure with the help of cynoacrylite (CN). As the strain generated in the material under explosive load is dynamic in nature, so TML make modular high bandwidth amplifier each having bandwidth of 200khz were used to condition the outputs of strain gauges. The conditioned outputs from strain gauges were recorded using data acquisition system having bandwidth greater than 200 kHz. High speed photography has also been used to capture the transient deformation of the cylimderical structure during the detonation.. The acquired strain data in instrumented trials has been used in determining the strain limit of austenitic stainless steel SS316 under high strain rate in explosive environment.
DAMAGE FAILURE AND SAFETY OF POLYMER BONDED EXPLOSIVE CHARGES UNDER IMPACT LOADING
As energetic composite materials, polymer bonded explosives (PBX) are composed of highly filled explosive crystals and a small of polymer binder. Accidental explosion could occur under low velocity impact. The ignition mechanism has drawn great attention to scientists and engineers. Hotspot is considered to induce the occurrence of ignition. Our works focus on the relation between the microcrack evolution and hotspot formation. The deformation, damage and failure behavior of PBX was investigated by split Hopkinson pressure bar, gas gun impact and penetration. In these dynamic loading experiments, the microstructure of the recovered specimens was analyzed by scanning electron microscope. It reveals that the cracking along the interface between the explosive crystal and the polymer binder under the tension, while the intergranular fracture is the main mode under the compression. The numerical manifold method was developed to simulate the tension and compression behavior. The effect of the initial defect, the strain rate and temperature on the tension and compression behavior was analyzed. The fracture modes of the tension and compression match the dynamic experiments above well. The low impact ignition analysis was conducted by means of Steven impact test. The specimen size effect on the ignition was mainly focused. The ignition observation and ignition delay time were measured. Also, the ignition velocity and reaction level were discussed. In addition, based on Visco-SCRAM model, a mechanical-thermal-chemical coupling model was developed to understand the ignition behavior in Steven impact test. The effect of the impact velocity on the ignition was analyzed. The mechanism of the size effect on ignition was discussed. Different projectile shapes were designed to act on the specimen. The difference of the ignition among these projectiles was compared. Further, the model was applied to simulate the multi impact corresponding to the real application scenarios. Moreover, in order to refine the microcrack evolution, the tension-compression asymmetrical microcrack evolution was proposed. The stochastic distribution of the microcrack length and density produced the ignition uncertainty, and further based on the Monte Carlo method, the ignition probability was quantified. These simulations matched the experimental results well.
EFFECTS OF STRUCTURAL PARAMETERS ON THE SHOCK WAVE OVERPRESSURE CHARACTERISTICS OF A MULTILAYER COMPOSITE CHARGE
This work examined a multilayer composite charge composed of an internal explosive charge, an intermediate non-explosive material and an outer aluminized explosive arranged in a coaxial structure. Using numerical simulations, a back propagation (BP) neural network algorithm and experimental verification, the shock wave overpressure characteristics of multilayer composite charges s having various structural parameters and initiation modes were examined. The ratio of the shock wave overpressure increase from simultaneous initiation of the internal and external charges to that generated by initiation of the central single charge was used to assess the effects of the structural parameters, overpressure increase ratio and suitable ranges for these parameters were generated. The structure of the composite charge was then optimized based on BP neural network calculations. The reliability of the numerical simulation method was verified by actual static explosion tests of warheads.
STUDY ON THE FORMATION BEHAVIOR OF SILVER-COPPER ALLOY SHAPE CHARGE JET
Silver-copper alloy is a metal material with high density and excellent ductility. These performances make it very suitable for a liner material. This study investigates the characteristics of shaped charge jet formations with a silver-copper alloy liner, by experimental and numerical methods. Pulse x-ray photographic technology was employed to observe the jet formed by silver-copper alloy shaped charge. The result shows that the silver-copper alloy shaped charge forms a continuous jet. The jet become decondensed and a comet-like tail appears as the jet stretches, which is different from traditional copper jet. The simulated results strongly agree with the experimental results.
EXTREME TENSION WAVE: NECKING AND FRAGMENTATION
A typical cylindrical cased charge explosion has brought a great interest in the scientific community in terms of optimizing or prediction of fragmentation. The Mott’s theory has brought a scientific breakthrough in this area of study by providing an insight about the fragmentation behavior in rings or shells. This theory introduced a so-called ‘Mott’s wave’ during the sudden expansion of the cylinder, and thus, provides a clue to understand the size distribution of fragments during explosion. In this study, a series of hydrocode simulations with ANSYS Autodyn is used to identify the pressure profile in the high velocity necking area of metallic samples with the pull speed ranging 1~6km/s. The extreme tension pressure profile is evaluated by conservation equations based governing equations in the necking area. These equations provide a way to study the extreme sudden pull followed by necking and fragmentation. From a series of numerical observation, we were able to conclude that there is a high chance that cracks occur from the center of a sample during extreme tension, and the necking really is not the main driver of the crack formation during an extreme sudden pull.
NUMERICAL AND EXPERIMENTAL INVESTIGATIONS ON BEHIND ARMOR EFFECTS BY SHAPED CHARGES
The effects that occur after penetration of a vehicle armor are referred to as behind armor (BA)effects. These effects are often not taken into account in the performance description of shaped charges (SC). A total view of the performance of a SC offers the possibility to better describe them. For this purpose, a basic experimental concept was developed to characterize the effects. In addition, copper (Cu) and aluminum (Al) and their combination were chosen as liner material. Hydrocode SPEED simulations have been performed in 90 mm caliber, which serve as a basis for the design of the liners. For the production of the bimetallic liner, a Cu liner was coated with cold gas spraying using Al. First, jet penetration performance in mild steel and its velocity were measured. In the second part, the effects that occur behind the armor were examined in more detail. Pressure and temperature were measured in a specially designed pressure tube at different target strenghts (50 mm, 100 mm and 300 mm) and the residual performance was recorded. The same approach was used to characterize the fragments. After a series of 28 tests, it can be concluded that, in contrast to Cu, the Al liner has a measurably greater effect behind the armor. On the one hand, the measured temperature difference between the two liner (Cu; Al) was above 1000 deg C. On the other hand, as expected, the penetration performance of the Al liner amounts to 60% of the Cu liner. The evaluation of the witness plates shows that the BA effect of the Al liner is more powerful. It was shown that the fabrication of a bimetallic liner by cold gas spraying leads to a functional shaped charge. Furthermore, it was shown that the performance of the bimetallic liner lies generally between the respective values of the monometallic liner. In conclusion, it was demonstrated that the experimental setups provided the opportunity to investigate the individual characteristics of the respective shaped charges and to work out differences.
DESIGN OPTIMISATION FOR SHAPED CHARGE JET PERFORMANCE
The performance of a shaped charge warhead is a direct consequence of specific design features such as the liner geometry. By dynamically modifying the geometry of the shaped charge design through a newly developed hydrocode optimisation and parameter suite, we are able to rapidly assess and improve upon a SC baseline concept. The hydrocode IMPETUS AFEA is used to model the formation of a SC, using Jet Kinetic Energy, Mass, Velocity and Particulation as the performance metrics. By using the experimental shaped charge BRL, a Jet KE increase of 6.7% was achieved. Using a baseline design and a newly devised performance metric taking into account both Jet KE and particulation we were able to increase the performance by 9%.
ENERGY RELEASE CHARACTERISTICS OF LAYERED CHARGE ENVELOPED BY ALUMINUM POWDER/RUBBER MATRIX COMPOSITE
To investigate the energy release characteristics of layered charge enveloped by aluminum powder/rubber matrix composite, the composites containing aluminum diameter D of 1μm, 10μm and 50μm were prepared and the confined explosion experiments for charges with layer/explosive ratios of 0.39, 0.68 and 1.52 were carried out in a 1.3-m3 explosion chamber. The tungsten-rhenium thermocouple was used to measure the internal explosion temperature history within the chamber. It is revealed that the measured temperature was enhenced with the increase of mass of outer layers. When the ratio increased from 0.39 to 0.68 and 1.52, the peak temperature increased from 329K to 517K and 882K, respectively. It is revealed that the excessive mass of layers are not conducive to the full release of energy generated from combustion. It is found that the layer with an aluminum powder size of 10μm exhibits the best effect on raising the temperature after the explosion, indicating that the medium-sized aluminum powder can fully react with detonation product and release more heat, which is beneficial to realizing the thermal radiation damage.
EXPERIMENTAL RESEARCH ON A NEW METHOD OF UNDERWATER LAUNCH WITH HIGH EFFICIENCY AND LOW RESISTANCE
A new high-efficiency and low-resistance launching method for underwater gun is proposed. That is the underwater gas-curtain launch. By introducing part of the gas inside the chamber to the front of projectile to drive water inside the barrel out, a low-resistance gas passage is provided for the projectile motion in the bore. So, the problems of poor safety and low muzzle velocity of the traditional fully submerged gun is solved, and a better interior ballistics performance than the fully-submerged launch can be realized. The experiment is carried out using three underwater launch methods, namely sealed launch (with complex structure, and it is difficult to adapt to underwater shooting environment), fully-submerged launch and gas-curtain launch. The experimental results show that the muzzle velocity is 228.2 m/s while the maximum chamber pressure is 25.7 MPa of the sealed launch. However, the muzzle velocity is 172.8 m/s while the maximum chamber pressure is up to 116.0 MPa of the fully-submerged launch. While the new underwater high-efficiency and low-resistance launching method is adopted, the maximum chamber pressure is only 41.8 MPa and the muzzle velocity is 177.5 m/s. It can be seen that the maximum chamber pressure is reduced by about 64% under the same muzzle velocity, and the significant drag reduction effect of gas-curtain launch greatly improves the interior ballistics performance when compared with the existing fully-submerged launch. It is clear that, the maximum chamber pressure and muzzle velocity of the fully-submerged launch are 451.4% and 75.7% of the sealed launch, while the maximum chamber pressure and muzzle velocity of the gas-curtain launch are 162.6% and 77.8% of the sealed launch. Through the shooting experiment, the drag reduction effect of the newly proposed gas-curtain launch and the improvement effect on the interior ballistics performance are revealed.
BURNING RATE OF SMALL CALIBER PROPELLANT AS A FUNCTION OF TEMPERATURE AND PARTICLE SIZE DISTRIBUTION
Small caliber propellant performance is influenced by many factors. In this study, researchers investigated the influence of particle size and temperature on the performance of small caliber, ball powder propellant. Particle size is important as it provides the initial surface area available for a propellant to begin the deflagration process. The geometry of the grain will dictate the manner in which the deflagration progresses: progressively, regressively, or neutral. The initial temperature of the propellant also has a direct influence on propellant performance. Evaluations were conducted in a constant volume, closed vessel to obtain pressure-time data for the various experiments. The data were used to calculate the burning rate coefficient ( ) and pressure exponent ( ) of the propellant samples. Dynamic vivacity, relative force, and relative quickness values are also reported.
IDENTIFICATION OF EXPERIMENTAL FORM FUNCTION USING LUMPED PARAMETERS INTERIOR BALLISTICS MODELS
A method for identifying experimental form functions based on the results of interior ballistics modelling using lumped parameters models is presented. The function is defined as the relation between the ratio of the actual burning surface of a whole propellant charge, to the initial global surface of all propellant grains in the charge and the relative burnt mass of the charge. It is approximated by a function depending on several parameters. Values of the parameters are identified by fitting the results of the interior ballistics modelling to the measured maximum pressure value and the projectile muzzle velocity value. The identified experimental form functions are compared to the functions determined in closed vessel tests. The examples analyzed suggest that the use of the experimental form function enables us to take into account the process of ignition in lumped parameters models.
INSTRUMENTATION, EVALUATION AND TEST METHOD OF CARTRIDGE ACTUATED DEVICE (CAD) FOR AIRCRAFT APPLICATION
This research work describes a proficient method about the instrumentation, evaluation, and test method of cartridge actuated devices (CAD) using a velocity test rig (VTR) for aircraft applications. CADs are known as gas generating devices that are installed on various military aircraft of Naval bases and Air Force to perform a highly significant task such as deployment of parachute, catapult, ejection of seat, thrusters, release of bomb, cutting action of cable, fuel tanks etc. These devices produce high temperature and pressure combustion gases on initiation. As these devices are utilizing once in life time and their end use cannot be tested by non-destructive techniques. Therefore, such devices are developed with high quality and reliability. All the safety aspects are considered during various stages of development and testing. The device presented in this article has undergone rigorous qualification trials before assigning a useful and serviceable life. The projectile velocity was determined experimentally with a Doppler RADAR at cold and hot conditions. These velocities vary from 142.76 ms-1 to 164.23 ms-1. This study provides new insight into the measurement of projectile velocity using Doppler RADAR.
COMPARING LEAD-BASED (CCI 41) AND LEAD-FREE (RUAG SINTOX) PRIMER PERFORMANCE IN 5.56mm NATO
Previous work identified significant problems with lead-free primers reliably igniting propellant charges in 5.56 mm NATO and other cartridges. These problems include high incidence of misfires, increased barrel friction, and long ignition delays. To date, no lead-free primer has been identified which meets NATO ignition requirements and works with a range of propellant types after prolonged exposure to humidity. Ruag SINTOX primers are marketed to meet NATO specifications, but it was unclear how they would respond to exposure to humidity commonly encountered in real-world environments. This paper reports results of performance and ignition delay testing of lead-free Ruag SINTOX and lead-based CCI 41 primers after exposure to typical indoor ambient humidity (40-60% relative humidity) and 100% relative humidity for 8 months (both at ambient temperature). Tests were performed using four propellant types: Alliant Blue Dot (a flake powder), Hodgdon H4895 (a cylinder powder), St. Mark's SMP842 (a flash suppressed ball powder), and the Ruag ball powder that the SINTOX primers are paired with in Ruag's lead-free ammunition. The Ruag lead-free SINTOX primer performed comparably to the CCI 41 lead-based primer in all tests and met the NATO specification for ignition delay (< 4 ms), even after 8 months of storage exposed directly to 100% humidity.
EVALUATION OF EXISTING EQUATIONS OF STATE FOR THE MODELLING OF PROPELLANT COMBUSTION IN INTERIOR BALLISTICS
Increasing performance of an armament system often leads to increasing the maximal pressure inside the chamber or increasing the compacity of the system. Telescoped ammunition and the associated weapon (40 CTAS) developed by CTA International is a solution that combines both improvements. With the increase of maximal pressure, the equations of interior ballistics might not be appropriate anymore since the models were established when the pressure was moderated. The aim of this paper is to compare the potential candidates for the equation of state of the combustion gases in a high-pressure system, such as telescoped ammunition. Within this study, the following equations of state are studied: ideal gas equation, Noble-Abel equation, Van der Waals equation and virial equation. The study is divided in two: a first study for air as the coefficients needed are easily accessible in the literature and a second study for combustion products stemming from propellant combustion.
APPLICATION OF WAVELET THRESHOLD ALGORITHM OPTIMIZED BY CHAOTIC ADAPTIVE FIREWORKS ALGORITHM IN THE DE-NOISING OF MUZZLE RESPONSE SIGNALS
To extract the muzzle response signals effectively and reduce the noise in the signals, a novel de-noising method, i.e., wavelet threshold algorithm optimized by the chaotic adaptive fireworks algorithm, is proposed for the de-noising of the muzzle response signals. This method obtains the wavelet threshold by calculating the Stein’s unbiased risk estimate (SURE), and uses the chaotic adaptive fireworks algorithm to search for the global optimal threshold, which can avoid the threshold falling into local optimal value effectively. Meanwhile, a novel threshold function is adopted to keep the balance between the signal preservation and noise filtering. To verify the de-noising effect of this method, the wavelet threshold algorithm optimized by gradient descent algorithm and the wavelet threshold algorithm based on standard soft threshold function are introduced to compare the denoising effect of the Blocks signal, HeaviSine signal and the measured muzzle response signal under the interference of Gaussian white noise. The results show that the proposed method can effectively suppress the noise while retaining the details in the muzzle response signal, and exhibits a promising prospect in practical application.
QUANTIFICATION OF THE WEAR EFFECTS ON THE PERFORMANCE OF SMALL CALIBRE GUNS
Internal barrel wear is considered as a key factor which affects the performance of small caliber guns in their different life stages. In order to improve the accuracy and the effectiveness of weapons, a wear analysis is deemed essential. The main aim of this research is the establishment of a new wear quantification technique using the profilometry method to quantify the influence of erosion on the performance of the gun. Thus, a Zeiss Micura Coordinate Measuring Machine (CMM) equipped with the VAST XTR gold high-end sensor and two NATO small caliber guns (5.56x45 mm and 7.62x51 mm) are considered. In order to quantify their wear volume after every N shots cycle, firstly, a new measurement approach is developed. Secondly, an uncertainty analysis is carried out for each measurement. Finally, a piezoelectric high-pressure transducer is used to measure the pressure inside the barrels after each CMM measurement. In order to evaluate the relationship between the latter and the wear volume, an experimental database is developed. The results show a similar correlation for the two NATO small caliber guns.
VARIATIONS IN BOLT FACE FORCES IN SMALL CALIBER WEAPON SYSTEMS DUE TO CARTRIDGE CASE MATERIAL
When a round is fired in small arms applications the pressure in the cartridge case imparts significant force on the bolt face and in turn the bolt lugs. As several efforts are underway to replace brass with lighter or stronger materials it is of utmost importance to characterize how these materials effect the forces seen by the bolt face. In this report a test fixture is developed that can measure the force seen by the bolt during firing. Modeling is also performed to determine its predictive capability in this application. It is shown that the cartridge case material has a significant effect on bolt face forces. Based on material selection bolt face forces can increase by approximately 66% for a similar pressure load. It is further shown that Finite Element Analysis is a useful tool in predicting bolt face forces within 10% of live fire testing.
INFLUENCE OF RELATIONS DEFINING PROPELLANT GASES—BARREL HEAT TRANSFER ON CRITICAL BURST LENGTH OF 35 mm ANTI-AIRCRAFT CANNON
The paper presents a review of propellant gases – barrel heat transfer relations and their influence on results of interior ballistics simulations for an artillery system. During simulations the lumped-parameters model of interior ballistics was applied. The thermal processes were calculated using the distributed-parameters model and resulted in barrel temperature changes estimation. Taking into account the high fire rate of investigated system – i.e. anti-aircraft cannon – the influence of applied heat transfer definition on critical burst length was estimated. Various considered formulae provided wide interval of obtained critical burst length for investigated system.
NUMERICAL STUDY ON PROJECTILE STOPPAGE INSIDE THE GUN BARREL
The effect of projectile stoppage inside the gun barrel is simulated using unsteady CFD simulation carried out using ANSYS Fluent Software. Nominal in-bore motion of the projectile is simulated using moving zones with sliding mesh approach. A special in-house developed user defined function is used to implement 1 DOF motion of the projectile. Abel- Noble equation of state is implemented in order to capture internal ballistics accurately. Projectile base pressure obtained from CFD simulation shows close agreement with the analytical data. The projectile stoppage is simulated by decoupling mesh motion from 1- DOF model. A pressure rise at the base of the projectile is estimated for stoppage of the projectile.
DETERMINATION OF GUN PROPELLANT BALLISTIC PARAMETERS WITH A FOCUS ON FLAME SPREAD AND GRAIN DIMENSIONAL VARIATION
In interior ballistic simulations, the burn time can be affected by the burn rate, propellant dimensions and flame spread. Standard IB models assume that grains are symmetric with no variation in dimensions, with instantaneous homogeneous ignition. This paper evaluates the contribution of grain dimensional variation (specifically the web), asymmetry and flame spread in a single base propellant with a single perforated grain geometry. It is shown that flame spread has the dominant effect on burn time, followed by web dimensional variation and lastly asymmetry. The implementation of these effects also leads to a simulated result that is more representative of the experimental curve in the closed vessel especially in the burnout phase.
SIMULATION RESEARCH ON FLOW FIELD DISTRIBUTION IN ARTILLERY TURRET UNDER THE SIMULTANEOUS ACTION OF EXHAUST FAN AND BLOWER
Aimed at the problem of after multiple firings of vehicle-mounted artillery, the gas in the turret remains, and the concentration is high, which endangers the safety of personnel in the tower. When the blower and the exhaust fan are working at the same time, a numerical simulation study based on computational fluid dynamics is carried out, and the flow field distribution results under different fan power working conditions are obtained. The simulation results have important reference significance for understanding the changing law of the medium in the turret under the action of the fan and the selection of the fan.
LOW TEMPERATURE SENSITIVITY ROCKET PROPELLANT
The purpose of this effort is to develop propellants with reduced oxygen balance and low molecular weight. This is to achieve increased performance results as well as low temperature and pressure sensitivity characteristics. Theoretical estimates of heat formation for these molecules were made and propellant performances were calculated. In these materials, as the oxygen balance was decreased, a lower temperature sensitivity could be achieved as well as a higher specific impulse and an increase in the drop height. The propellant should have a high but steady burn rate that exhibits low-pressure and temperature sensitivity. The main objective of this study is to characterize and evaluate a new energetic plasticizer. This will be comprised of a eutectic mixture of linear dinitrodiazaalkanes energetic materials, named as DNDA-57. This will consist of numerous chemical and thermal characterization, including safe handling and small scale sensitivity testing. This paper will discuss the DNDA-57 material evaluation at a preliminary level.
DYNAMIC MEASUREMENT OF THE PROJECTILE MOTION RESISTANCE AND THE INFLUENCE OF PROJECTILE MOTION RESISTANCE ON INTERIOR BALLISTICS PERFORMANCE
The motion resistance of projectile in gun barrel has an important influence on the interior ballistic performance. But it is difficult to measure the motion resistance of projectile because there exists high temperature and high pressure gas in the gun barrel. Firstly, this paper designs and manufactures the measurement devices which contains the projectileborne recorder, the shell and the test-projectile. Then the gun launch test is carried out with these devices, and the projectile motion resistance is calculated according to the test data. Secondly, the two-phase flow interior ballistic model is established and solved. Finally, the influence of the projectile motion resistance on the interior ballistics performance, such as pressure wave and projectile muzzle velocity, are simulated and discussed.
BARREL HEATING IN HYPERVELOCITY POWDER GUNS
When a gun fires, hot propellant grains and gas heat the barrel. The first phase of heating is the in–bore period (i.e., action time). During this period, the projectile travels down the barrel to the exit plane of the muzzle. The second phase of barrel heating is “blowdown.â€ When the projectile leaves, the hot high–velocity gas expands and accelerates, rushes out of the barrel, and sweeps forward over the projectile. The blowdown time is not a definite measurable quantity like the action time. The gas vents out of the barrel according to exponential decay formulas of gas dynamics. Mathematical models and results are provided for both phases of heating. For velocities over 1,000 m/s, radiation is the dominant mechanism. Conduction during blowdown is a large contributor.
TOWARDS A DROP-IN REPLACEMENT SUBSONIC CAPABILITY FOR NATO SMALL ARMS
While subsonic ammunition has been of military interest for years, particularly for covert operations, significant limitations of current offerings have prevented its adoption including the inability to cycle an automatic action. This and other limitations were investigated through a design exercise to establish the feasibility of a drop-in replacement relevant to the Canadian Armed Forces using commercial off the shelf components. A survey and stability analysis of commercially available 5.56 mm projectiles led to the selection of the 90 grain Sierra Matchking for this design. Three different cartridge configurations were investigated in order to evaluate the effect of reducing cartridge volume on key internal ballistic variables. A cycling impulse model was developed in order to rank candidate designs on their ability to cycle a prescribed automatic weapon. Cartridge volume, in terms of standard cartridge, straight internal bore, and custom internal diameter to realize 95% load density, was explored as a means of increasing the load density of subsonic ammunition in order to reduce muzzle velocity variance and thus increase accuracy. However, the accuracy gained by reducing cartridge volume is shown to cause significant tradeoffs in cycling impulse. Live fire testing was performed in order to determine the minimum cycling impulse required to cycle the test weapon. The results also indicate that there may exist a threshold load density above which load density does not play a significant role in muzzle velocity variance. Thus, an objective of maximizing load density may overconstrain the design for minimal benefit.
When a gun fires, hot propellant grains and gas heat the barrel. Repeated firing causes barrels to become very hot. If a cartridge is loaded into a hot barrel and, for whatever reason, cannot be promptly fired or ejected, a potentially dangerous situation exists. The round may cook–off. With explosive loaded ammunition, there is the main charge and usually a fuse. The fuse can contain a number of pyrotechnic devices, e.g. time delay charge, booster for detonating the main charge, and multiple divert charges for guidance systems. If any of these cook–off, there may be serious consequences, including complete destruction of the weapon, damage to vehicles or ships, and loss of life. The paper provides a mathematical analysis of heat flowing into a cartridge from a hot barrel. Cook–off is explained. We show how to apply data from routine fast cook–off safety tests to projectile heating.
OVERRAMMING 16-INCH GUN PROPELLANT CHARGES
There was an explosion in the center gun of a 16-inch gun turret. The paper describes an investigation to see if the explosion could have been caused by over ramming the propellant charge. A sprocket driven chain pushes the projectile, then the charge, into the gun. A computer model was developed to calculate the response of a 16–inch charge assembly to overramming. The calculations with without explosions were studied to explain the physical process that results when an overram occurs: A strong stress wave starts at the contact point between the charge and projectile and propagates rearward through the charge assembly. Fracture of propellant grains can cause a spark that can ignite the 660 pound charge. When this occurs, the rammer and chain are driven violently backward by an explosion. The serpentine shape of the chain and its deep impression in the loading tray were accurately calculated.
NUMERICAL SIMULATION OF A NAVAL GUN CHARGE
Chamber cleaning projectile is one of the auxiliary projectiles equipped with a naval gun. It is an air explosion projectile without projectile. It is used to clean up the projectile retained in the chamber for special reasons or remove the residue in the chamber after launching the projectile. In this paper, based on the internal ballistic theory and one-dimensional twophase flow theory [1-3], the one-dimensional two-phase flow internal ballistic model of ordinary grenade is established, and the internal ballistic simulation calculation of the launching process of grenade is carried out. On this basis, the projectile mass is adjusted to 0, and the cleaning process of cleaning projectile is simulated. The simulation results show that when there is no projectile loading, the pressure established in the bore is very low and the propellant burns slowly. Because there is only a sealing cover at the front end, the frontend gas forward impulse speed is very fast, and the pressure in the bore decreases along the barrel, forming a large pressure gradient without negative pressure difference. The calculated negative pressure difference is 0, It shows that the internal ballistic process of launching clean chamber projectile is safe [4-5]; In addition, the calculation shows that a high-speed forward flow will be formed in the whole bore during the firing process, and the gas velocity is much higher than the initial velocity of the general projectile. This highspeed flow is conducive to removing the oil stain in the bore or the residue in the bore after the firing of the whole cartridge. The model test results provide a certain reference for the safe use of the ammunition.
ON THE TECHNICAL WAYS TO IMPROVE THE MUZZLE VELOCITY OF A CALIBER ANTIAIRCRAFT GUN
With the development of missile technology, the combat mission of antiaircraft artillery has changed from attack to defense. Due to its light weight, large ammunition reserve and continuous firing for a long time, medium caliber antiaircraft artillery is still an effective weapon against high-altitude, hollow and shore attacks [1-3]. In order to further improve the survivability of the ship, further shorten the reaction time of the weapon, improve the firing accuracy and shorten the flight time of the projectile are the main technical means that can be applied. The muzzle velocity is the main factor affecting the flight time. Based on the latest development of internal ballistics and charging technology [4-5], this paper calculates and analyzes from the aspects of lengthening barrel, using sub caliber projectile, using Dun propellant technology with high increased surface and high loading density, increasing the maximum chamber pressure of gun and increasing the volume of gun chamber, obtains the influencing factors of increasing muzzle velocity, and focuses on the feasibility of increasing muzzle velocity. The analysis shows that in order to increase the muzzle velocity of 76mm gun, lengthening barrel, increasing chamber pressure, adopting insensitive propellant technology and reducing projectile weight are the main factors affecting the muzzle velocity of 76mm gun, while increasing chamber volume has little effect. Therefore, the muzzle velocity of the gun should be greatly increased. If the barrel is extended by 1m (the extension increase is 22%), the sudden propellant is used (the charge amount is increased by about 14%), the projectile weight is reduced to 3.5kg (the reduction range is 40%), and the chamber pressure is increased to 400MPa (the copper column pressure is about 357mpa, increased by 20%), the muzzle velocity can reach 1398m / s, and the muzzle velocity increase range is 42.6%. The analysis of this paper provides a certain reference for the technical transformation of a caliber gun.
RESEARCH ON LOW OVERLOAD EJECTION OF SMALL PROJECTILE BASED ON PROPELLANT GAS
With the rapid development of artificial intelligence technology, intelligent projectile is gradually becoming an indispensable weapon in modern high-tech war. Small low-cost intelligent projectile has the advantages of good concealment, strong mobility and high combat efficiency cost ratio [1-2]. The development of intelligent projectile is an important link in the process of carrying out combat tasks, which directly determines whether the aircraft can take off smoothly [3]. Small low-cost intelligent projectile must meet two conditions: (1) have a certain high orbit speed to maintain aircraft stability; (2) In order to meet the demand of low cost, the impact overload borne by the guiding head, communication module and other components of projectile is limited, that is, the launching process of projectile must have low overload characteristics. Scholars from various countries have developed extensive and indepth research on the ejection methods of small projectiles, including high-pressure gas ejection [4], electromagnetic ejection [5], rocket assisted ejection [6], artillery direct launch [7] and ejection launch [8].According to the low overload ejection requirements of a small low cost intelligent projectile, a method was proposed to realise low overload ejection of the small projectile by using propellant gas based on the high-low pressure launching theory. The interior ballistic mathematical model of the projectile ejection was established and the numerical simulation was finished. Based on the simulation result, a low overload ejection device for propellant gas was designed. With this device, an ejection experiment study of the small intelligent projectile was carried out. The test results indicate that while the impact overload of the projectile is less than 60g ï¼Œ the velocity the projectile leaving the barrel is more than 45m/s. The experimental results show that it is feasible to realize low overload ejection of small projectile by using propellant gas. The simulation results agree well with the test . The mathematical model can describe the projectile ejection process well. The research work provides theoretical and experimental basis for realizing low overload ejection process of small low cost intelligent projectile by using propellant gas.
THERMAL EFFECT INFLUENCE ON BULLET ENGRAVING PROCESS AND INTERIOR BALLISTIC PROCESS
The thermal effect cause by continuous firing of firearms, generally recognize have influence on the movement of bullets during in-bore process. In order to understand this influence. A finite element model coupled thermal and structure which contained bullet and barrel was established. Through the classical interior ballistic theory, the distribution and variation law of the boundary and load conditions parameters in the bore were determined, such as base pressure, propellant gas temperature, forced convection coefficient. By loading the boundary and load conditions at different positions in the barrel versus real time, the temperature distribution and deformation of the barrel after different initial temperatures and multiple continuous firing, the changes of the structure and movement parameters of bullets were calculated, and the model was validated by the temperature distribution of the barrel surface through the experimental test. The research shows that the thermal effect has a great influence on the engraving resistance of bullet, but the trajectory was little. The structural characteristics of the bullet change greatly with the increase of temperature. In addition, the thermal effect has a great influence on the vibration speed of the barrel muzzle, which may further affect the firing accuracy. Generally, when the barrel temperature is below 200 ℃ , the thermal effect has little influence, and when the barrel temperature is above 200 , the negative influence caused by the thermal effect increases linearly.
THE PERFORMANCE OF PNEUMATIC GUN LAUNCHING SPHERICAL PROJECTILE
Pneumatic guns can fire spherical projectiles of multiple materials, and some pneumatic guns can be modified and replaced with barrels. In order to clarify the impact of the pneumatic launching structure and the physical characteristics of the projectile on the launching ability of the pneumatic guns, an internal ballistic analysis model was built to describing the process of launching projectile of the gun, which accounted the process of charging and discharging, and the feasibility of the model was verified by a trial calculation with a certain pneumatic gun structure parameter Based on the model, the influence of gun/projectile characteristics on the firing ability of pneumatic guns was analyzed. The research shows that the firing ability of pneumatic guns is related to the pneumatic firing structure. Under the same conditions, the higher density of the projectile, the higher specific kinetic energy could be acquired, and the ratio of the specific kinetic energy of the higher density projectile to low density projectile is less than the density ratio; under the condition that the barrel can be modified and replaced, the barrel caliber is changed, the smaller caliber, the higher specific kinetic energy that the projectile can obtain, and the change of barrel caliber length does not affect the ratio of specific kinetic energy obtained by projectiles of different densities.
THE DIFFERENCE BETWEEN THE CANNON JUMP PREDICTION OF HE-MP VS APFSDS PROJECTILES— COMPARATIVE STATISTICAL ANALYSIS
The article is a continuation of a study that allows to predict the cannon jump based on the barrel curvature using a linear regression model. In the past, this capability was formulated mainly for APFSDS projectiles, while in the current work an attempt was made to match this methodology to full-caliber ammunition, using a significant fire tests database. During the study, there was a major difficulty in building a prediction model which has smaller error than the average cannon jump value based on full database information, and the authors hypothesized that the probable reason is a large residual error of jump value which presents in rounds with relatively large dispersion dimensions. For the test, the results were grouped according to the threshold value of the dispersal size, and a clear improvement trend was identified in the model errors as the threshold for dispersal size was tightened.
QUANTIFYING HANDGUN RECOIL WITH HIGH SPEED VIDEO
In principle, handgun recoil is predictable using conservation of momentum and known mechanical laws. In practice, recoil is often considered subjective. The current study employed high speed video recording at 10,000 frames per second to quantify recoil of 11 different pistol loads representing a range of bullet weights and velocities in three different cartridges (9mm NATO, .40 S&W, and .357 SIG) fired from the same Sig P229 auto-loading pistol with the appropriate caliber barrel. Kinematic variables quantified by analyzing the video included: slide velocity, frame velocity, frame angular velocity, slide acceleration, frame acceleration, and frame angular acceleration. The correlation of these quantities with bullet momentum estimates suggests that the video method is reliable for quantifying handgun recoil and shows promise for testing models purporting to predict handgun recoil from mechanical laws. Future work should be able to test effects of recoil reducing devices and determine which kinematic variables are the best predictors of ergonomic effects such as accuracy and shot-to-shot time intervals.
ON THE QUANTITATIVE INVESTIGATION OF THE INTERMEDIATE BALLISTICS: VELOCITY MEASUREMENT OF THE MUZZLE FLOW
In the context of intermediate ballistics, a thorough understanding of the muzzle flow is necessary to optimize the design of muzzle devices and long-range projectiles. However, due to the harsh environment, the extremely short duration, and the transient evolution of the intermediate ballistics phase, both experimental and flow modeling efforts are hampered by the lack of quantitative experimental data. In this study, a Particle Imaging Velocimetry (PIV) experimental set-up is implemented to quantitatively investigate the muzzle flow based on its velocity. This tool has the advantage of obtaining a non-intrusive and whole-field diagnostic, both qualitatively and quantitatively. The first part of the study explains that PIV is suitable for measuring the velocity fields of the muzzle flow. This was achieved by using the naturally present particles in the gas as tracers. We demonstrate that the raw PIV images revealed that the structure of this flow is composed of two regions. The first region is located within the under-expanded jet and consists of spatially dispersed particles. The second region, downstream of the Mach disk, is formed by large structures. We show that cross-correlation and particle tracking velocimetry (PTV) algorithms can determine the flow velocity in both regions. In the second part, we present a quantitative description of the muzzle flow issued from the launch of a subsonic .300 Blackout projectile. The results show that these gases reach a maximum centerline velocity of more than 900 m/s inside the shock bottle. At the barrel exit plane, the gases start to discharge with a velocity close to that of the projectile’s launch velocity, accelerating it. In the third part, we present a detailed comparison between the aforementioned flow and the flow resulting from the launch of a supersonic projectile. Differences and similarities are pronounced and explained. The presented set-up and the description of the whole flow field velocity would serve as valuable improvements toward muzzle devices optimization and numerical code validation.
INTERIOR BALLISTICS MODELLING FOR 40 mm CASED TELESCOPED AMMUNITION
Cased telescoped ammunition and associated cannon is a proven disruptive technology in medium calibre weapons, allowing increased lethality in a compact, multi role weapon system. From new ammunition development to support of serial production, an internal ballistics model is key to highlight design margins, support design improvement and performance increase. The architecture of the cannon and the ammunition result in a very specific internal ballistics mechanism which makes standard models unsuitable. This paper will detail the different steps of the internal ballistics cycle of the 40 mm cased telescoped ammunition and explain how each steps were studied from both theoretical and experimental point of view and aggregated to achieve the internal ballistics model of the CT cartridge.
DESIGN, SIMULATION AND EXPERIMENT OF PROTECTIVE STRUCTURE FOR ANTI-HIGH OVERLOAD FUZE
The fuze withstands high overload in the electromagnetic launch. The design of an antielectromagnetic launch overload structure draws much attention in the field of the fuze. In this paper, anti-high overload structure of the fuze is designed by analyzing the environmental factors in the electromagnetic launch. Then mechanics analysis and calculation are investigated. Nextly, the finite element simulation model is established. Based on this model, the stresses and deformations of the fuze in different protective conditions are analyzed during a high overload environment. The best protective scheme is selected. The theoretical calculation and simulation analysis results show that the max stress of the structure is less than the tensile strength of the material and the deformation is very small. Finally, the experiment of the electromagnetic launch is executed, and verification of the fuze is ultimately performed. In conclusion, the designed structure of the fuze can meet the anti-high overload requirement.
EFFECT OF WEAPON SOUND SUPPRESSORS ON DISPERSION: AN EXPLANATION
A widely perceived idea that circulates among the marksmen and sniper community is that rifles equipped with sound suppressors will yield nonnegligible reduction in dispersion when compared to that obtained from the same rifle under the same firing conditions. In order to verify and quantify this assertion, an experimental investigation was carried out to verify the effect of suppressors on the observed dispersion. Firing were performed indoor at 200 m using a bench mounted Mann barrel fitted with a Remington bolt action 700. The ammunition used for the trial was the Remington .223. A commercially available mono-core sounds suppressor was used for the trial. The results show a clear reduction in dispersion when firing the weapon using the sound suppressor. Orthogonal high-speed cameras located at 1 m from the muzzle were used to document the first maximum yaw for each projectile fired. On average, the first maximum yaws were found to be smaller when using the sound suppressor. This indicates that the gas flow around the projectile within the suppressor acts as a projectile stabilizer following its exit from the barrel.
DYNAMIC ANALYSIS AND OPTIMIZATION OF A CASED TELESCOPED AMMUNITION GUN BASED ON THE SOFT RECOIL TECHNOLOGY
Aimed at the object of the recoil minimization of a cased telescoped ammunition (CTA) gun with the soft recoil system, a dynamic model was established based on the characteristics and the assumptions of the fire-out-of-battery (FOOB) principle and dynamic characteristics were obtained by numerical simulation analysis. Based on these results, an optimization model was established to reduce the recoil, and the key parameters of the firing platform were optimized by the optimization algorithm. The simulation results show that the maximum recoil was reduced about 10% without affecting system performance, which effectively improved the firing stability and the overall performance of the weapon system.
KINETIC ENERGY PROJECTILE LAUNCH USING LIFE SEPARATION SABOTS
The purpose of the present work is to visualize the separation dynamics of a new lift separation sabot. Conventional sabots used for launching kinetic energy projectiles are a major contributor to the dispersion of the penetrator due to the mechanical interaction between sabot and the penetrator during separation. A sabot with an aerodynamic lifting surface close to the center of gravity is designed and launched from a 25mm caliber gas gun. The visualization results show that the sabot is separating from the penetrator with less rotation of the sabot which leads to less mechanical interaction between the latter and the former.
ANALYTICAL ESTIMATION OF THE PROJECTILE TRAJECTORY AND DRAG CHARACTERISTICS IN THE INTERIOR AND TRANSITIONAL BALLISTIC REGIMES
The highly complicated and unsteady flow phenomena associated with a moving projectile in the interior and the transitional ballistic regimes are modelled analytically. It is attempted to estimate the unsteady aerodynamic forces generated on a supersonic projectile launched from an aero-ballistic range using a Lagrangian approach. A comprehensive analytical model is proposed to predict the entire projectile motion right from its start in the launch tube until it enters the exterior ballistic regime. Inviscid axisymmetric flow is considered in the interior and the intermediate ballistic regimes with isentropic assumptions except at the shock locations. The model provides a first-hand estimate of the projectile aerodynamic characteristics launched from a ballistic range with less than 5% error when compared to the computational results in the muzzle properties, which provides valuable design data for the ballistic range designers.
INFLUENCE OF 155 mm HOWITZER’S MUZZLE BRAKE ON RECOIL SYSTEM WORK IN MATTER OF SHOOTING WITH SHOT IMITATOR AMMUNITION
Following paper focus on disabling muzzle brake to increase kinetic energy of recoil assembly. In 155 mm howitzer increasing mass of projectile cause danger for surroundings. Increasing mass of proppelants in not a wise option. The imitator should have to imitate a real shot with the same propellant conditions as live ammunition. The paper presents influence of muzzle brake on breech force, and possibility of disabling muzzle brake during shots with imitated ammunition. It also contains information observed during shooting tests.
HAZARD CLASSIFICATION OF PLASTIC BONDED EXPLOSIVE AS INSENSITIVE MUNITIONS BASED ON RESPONSE TO VARIOUS STIMULI BY SIMULATED TESTS CONDUCTED ON SCALED DOWN WARHEADS
It is popularly said that ‘sailors in the navy sleep on the ammunitions’ as they sail onboard naval platforms such as ships and submarines for extended periods. Hence, navies worldwide assign utmost importance to safety. In order to meet the requirements of safety against various stimuli under different threat perceptions in the real scenario, scaled down warheads filled with RDX/AP/HTPB based Plastic Bonded Explosive (PBX) are subjected to prescribed standard tests. The tests conducted are Bullet Impact Test, Fragment Impact Test, Slow Cook-Off Test, Fast Cook-Off Test, Shaped Charge Jet Penetration Test and Sympathetic Detonation Test. Preparation of specimen scaled down warheads, test methodologies and ANSYS Autodyne simulations are discussed in the present paper. Actual details of the tests conducted are not revealed to confidentiality.
COMPARATIVE INVESTIGATIONS ON BALLISTIC BACKFACE DEFLECTIONS OF COMBAT HELMETS USING FORCE MEASUREMENT AND DIGITAL IMAGE CORRELATION
In the present work two different measurement methods are compared for the analysis of ballistic caused “dynamic backface deflectionsâ€ (BFD): a conservative force measurement and an optical measurement with digital image correlation (DIC). An aramid fibre combat helmet, meeting the requirements of VPAM 3, was analysed with the two methods under the same ballistic conditions (frontal impact, 9 mm x 19 full metal jacket (FMJ); 410 m/s). The force measurement resulted in a cumulative total force of 7.2 kN. A maximum BFD of 22 mm at a maximum speed of 110 m/s was determined using the DIC method. Both methods showed a constant load duration respectively deformation duration of 0.5 ms while the noncontact DIC measurement method resulted in a 120% deeper permanent BFD. Considering the significant limitations of both methods, the force measurement method was evaluated as the more advantageous method for further analysis of realistic, ballistic caused blunt head loads.
BENEFITS OF TAKING INTO ACCOUNT THE STATISTICAL VARIATION OF WARHEAD EFFECTS IN V/L SIMULATIONS
This paper deals with modeling of weapon as input data for vulnerability / lethality simulation. This kind of simulation is very commonly used in acquisition programs. These models are used in lethality and vulnerability codes to assess the interaction of weapon effects with targets. This document will present a more realistic model of high explosive warhead effects in Vulnerability/Lethality (V/L) codes. The classical terminal ballistic models used in V/L calculation usually give a single value of penetration / perforation capacity for a given configuration. Our idea is to improve our models by taking into account the random aspect of terminal ballistics and warhead mechanics. These random phenomenon’s need to be included in simulations to obtain higher fidelity and accuracy in the results.
REVERSE LETHALITY AND TRAJECTORY MODELING FOR A FORENSIC APPLICATION
This article concerns part of the forensic analysis performed in the aftermath of the MH17 incident, when a civilian airliner was downed over the Ukraine in July, 2014. This analysis was performed in the framework of the international Joint Investigation Team (JIT) created to investigate this incident. The article describes the followed approaches to determine the likely launch area of a BUK 9M38(M1) missile assumed to be responsible for downing the MH17 aircraft, based on a reverse lethality and trajectory modeling in three distinct phases. Firstly, the likely point of detonation in reference to the aircraft fuselage of flight MH17 was determined. In a second phase, the likely orientation of the missile was determined by matching the damage pattern as seen on the reconstructed MH17 fuselage to the dynamic fragmentation pattern of the warhead of the considered missile system. Finally, using a flyout model for the missile system, the likely launch area of the missile was determined as requested by the Joint Investigations Team. Although the different steps are not new in the field of ballistics, their reverse application and the case to which these were applied makes this work unique and might serve as a basis for any future similar cases that might arise.
DETERMINING THE LETHALITY OF A HAND GRENADE AGAINST PERSONNEL TARGET USING AVAL
Kill probability as a function of distance is important for a hand grenade since it influences the lethality and minimum safe distance when using it. Measured characterised fragmentation information was used as an input into the AVAL lethality simulation software to make predictions against personnel targets. The direct nature of engagement between the hand grenade and the personnel target make AVAL the ideal simulation code for this type of prediction, not dissimilar to the direct engagement of other warheads with more complex targets such as aircraft, unmanned aerial vehicles or fighting vehicles. The kill probability of the hand grenade was evaluated as a function of distance from the target with various orientations to achieve an average expected kill probability. From these kill probabilities it was possible to determine lethality and the safe radius for the user. It was found that the kill probability was significantly reduced by the vest of the soldier for all distances investigated.
FINITE ELEMENT (FE) EVALUATION OF DYNAMIC COMBAT HELMET TRANSIENT DEFORMATION CONTACT AREA ON A HEADFORM
Current ballistic helmets are designed to protect the head from penetrating threats. The compliance of composite helmet materials allows for ballistic transient deformation (BTD) of helmets that defeat a threat. These BTDs can result in a unique set of injuries known as behind-helmet blunt trauma (BHBT). Quantifying the loading behind the helmet to help understand the risk for BHBT has been challenging because the BTD occurs at high velocities with high loads that is obscured by the helmet itself. For this study, finite element (FE) simulations of a combat helmet, with and without a suspension system (i.e., pads), impacted by a ballistic threat were performed to evaluate contact area and regional force concentrations of BTD on a headform surrogate. Overall, the results indicate that the helmet pads significantly influence the contact area and magnitudes of the loading from BTD. The loading behavior differed between the front and side helmet impacts, most likely from differences in the position of the pads relative to the center of impact. Understanding the spatial and temporal evolution of loading on the head, and the components of the protection system that influence the loading is important to identify potential vulnerabilities or design strategies for combat helmets.
HUMAN BODY MODEL RIB RESPONSE TO SOFT AND HARD ARMOR BALLISTIC LOADING
Personal body armor back-face dynamics are the driving force for behind armor blunt trauma. The potential timing for blunt force rib fracture was investigated using finite element analyses of soft and hard armor impacts against anterolateral ribs of a human body model. Armor back-face dynamics were acquired from experiments using soft and hard armor backed by gelatin and clay, respectively. Analysis of the simulations identified fracture-level maximum principal strain magnitudes for cortical rib tissue at times that were within the first tenth of the event and over 20 mm short of the peaks armor back-face displacement. These findings suggest early armor back-face dynamics play a role in blunt force injury outcome.
EXPERIMENTAL VERIFICATION OF TNT EQUIVALENCE TO PE4 CHARGES USING A BLAST TEST DEVICE
A considerable amount of scientific effort has been expended over many decades on developing means of predicting the loading generated when a blast wave impact structures. The energetic output and the blast load associated with the detonation of a mass of high explosive will differ depending on the chemical composition of the explosive itself. It is therefore convenient to equate the effects of an explosive to TNT. The “TNT equivalent (TNTeq) ratioâ€ refers to the mass ratio of the explosive in question that will produced equal peak overpressure to that equivalent mass of TNT. There is vast range of equivalency ratios for PE4 in the literature. However, there appears to be no research that determines effect of TNT equivalency of spherical shape of PE4 charge detonated on rigid ground surface This paper presents experimental measurements of reflected pressure-time histories from a series of well-controlled small scale blast tests. An investigation of TNT equivalent ratio of spherical PE4 charge detonation on rigid ground was performed using the Blast Test Device (BTD). Our results presented here clearly demonstrates that the TNTeq ratio of 1.37 is higher in the near field environment and TNTeq of 1.2 will be the best to produce blast wave by the hemispherical PE4 detonations on rigid surface. It is also better to compare the peak pressure rather that the injury caused by the pressure profile.
A SYSTEMATIC SCENARIO-BASED APPROACH OF MORTAR FIRE DANGER ZONES CALCULATION
In this work the authors suggest a method for calculating surface danger zones in mortar fire. This problem plays a major role in the operation of this weapon, mainly out of safety considerations for operating troops and uninvolved civilians. The study presents a systematic methodology for calculating the danger zones according to the specific shooting scenario, unlike using a fairly strict danger zones as has been customary so far. The method is based on a combination of analyzing the ballistic flight and the probability of impact at a certain point and studying fragmentation characteristics around it. This combination defines a contour that describes the danger area that best suits the scenario according to the permitted risk level.
INFLUENCE OF MASS UNBALANCE ON A SMALL-CALIBER PROJECTILE TRAJECTORY
The purpose of this article is to use an uncoupled method based on Rigid Body Dynamics (RBD) and Computational Fluid Dynamics (CFD), to determine the aerodynamic coefficients of geometrically symmetric small-caliber projectiles but with a fixed mass asymmetry to complement previous findings in large caliber. In addition to having to take into account the evolution as a function of the yaw angle and the Mach number for the calculation of the coefficients, a common 6-DoF model is adapted to also take into account the unbalance position in flight without any modification of the twelve differential equations of motion. It appears very clearly that the effects related to the presence of the unbalance are much more important at the exit of the tube, than in air, since the orientation problems are quickly compensated by the gyroscopic effect whereas the direction of the trajectory is definitely deviated.
EXPERIMENTAL DETERMINATION OF PITCH DAMPING COEFFICIENTS USING A WIRE SUSPENSION
An experimental method for the determination of the pitch damping moment coefficient sum Cmq + Cm in a wind tunnel is presented. A low-interference wire suspension is used, thus enabling the investigation of projectile configurations in wind tunnels with a low-diameter test section at transonic Mach numbers. Two reference models, the Basic Finner and the Army-Navy Spinner Rocket (ANSR) are examined at Mach numbers ranging from 0.6 to 2. An evaluation procedure for estimating an average coefficient sum based on multiple tests at the same experimental conditions is outlined and validated using rigid-body simulations. The influence of the wires on the flow field is investigated in flow visualization experiments and CFD simulations. The method shows improved accuracy of up to an order of magnitude at transonic Mach numbers in comparison to free-flight tests. While the flow field changes significantly due to the wires, their influence on Cmq +Cm is shown to be negligible.
DIFFERENT OBTURATOR CONFIGURATIONS FOR PUSH LAUNCHED SABOTS
In this work several different obturator designs were explored for use with a four-petal, pushlaunch sabot design for a tungsten heavy alloy projectile. Stepped-top obturators resulted in higher average pitch values than flat-topped obturators. Single piece obturators of acetal or UHMWPE appeared to provide equivalent behavior; acetal appears to be more brittle than UHMWPE, but was easier to machine to tolerance. Two-part obturators functioned reliably and were less prone to result in secondary impact on targets. Aluminum and steel pusher plates offered comparable performance for the projectile and launch velocity considered. A Garolite G-11 composite pusher plate didn’t prove strong enough to function correctly. Shots with drag flares consistently had lower pitch values than shots without drag flares.
ESTIMATION OF THE VELOCITY OF A PROJECTILE USING RADIAL ACCELEROMETERS—VALIDATION ON 155 mm FREE FLIGHT TEST
This paper addresses the problem of velocity estimation for a 155 mm projectile. Indeed, to correctly feed the guidance and control algorithms of such a guided munition, it is essential to estimate its speed autonomously (without any external system) onboard and in real-time. Knowledge of the velocity (and thus the Mach number) is required to infer the aerodynamic coefficients governing its dynamics. From the analysis of the frequencies present on one of the radial accelerometers, and from a reduced 6DOF model describing the epicyclic rotation of the shell, we are able to estimate the velocity of the ammunition. The roll speed can be determined from magnetometers. For frequency estimation, we employ a subspace method of the Pisarenko type, relying on the auto-correlation matrix of the accerelometer signal. This matrix is estimated from samples and its dominant eigenvalues are related to the precession and nutation frequencies. In turn, the velocity can be estimated from the analytical values of the epicyclic motion. In this paper, we offer an efficient method to estimate the velocity of an artillery shell in free-flight, using only embedded sensors. The next step will be to use these results to improve the estimation of the projectile’s attitude and position.
A NOVEL METHOD FOR TANK GUN ERROR BUDGET ANALYSIS
In this paper, we present an accuracy model of a tank weapon system against small aerial targets. A medium calibre air bursting munition (ABM) hit probability against a low slow and small unmanned aerial vehicle (LSS UAV) is evaluated. The model is based upon stochastic propagation of errors through Monte Carlo simulations of the projectile and fragments trajectories. The combination of the probabilistic distributions of detonation point states with the fragments distributions allows the prediction of a probabilistic distribution of impacts. The inventory of error sources is done by an analysis of the weapon system fire control. The sensitivity of the munition dispersion to the different error sources is evaluated using the Sobol method for global sensitivity.
INCREASING THE ACCURACY OF THE RANGE CORRECTIONS FOR THE AIR VIRTUAL TEMPERATURE
If for any reason it is not possible to use an automated fire control system, then especially in combat conditions it is necessary to use an alternative method of calculating the mean point of impact position. To do this, tabular firing tables (TFT) are used together with the corresponding type of artillery meteorological message. If TFTs created according to STANAG 4119 are used, only the met message METB3Q must be used for surface-tosurface fire. The calculation of corrections for deviations in virtual temperature is very problematic. We have been dealing with the problem since 2013. In this article, we propose a solution that increases the accuracy of calculations and is applicable in combat conditions. However, the main advantage of the proposed method is the fact that met data can be obtained from any available met message (METB3Q, Meteo - 11 (meteo - average), METCMQ, METGM and GRIB).
NUMERICAL SIMULATION OF SABOT SEPARATION OF KINETIC ENERGY (KE) PROJECTILE
Fin Stabilized Armor Piercing Discarding Sabots (FSAPDS) are kinetic energy (KE) projectiles fired from Main Battle Tanks (MBTs) primarily meant to defeat armored tanks with the help of its high strength penetrator which pierces the armor plate due to its high impact velocity. The penetrator is usually made of tungsten alloy and are wrapped by 3 sabots, in general. Sabots support and accommodate the round within the barrel bore, as the penetrator has caliber lesser than the bore of the barrel. When the projectile comes out of the barrel, sabots separate under the action of aerodynamic forces. During separation, the projectile is exposed to higher supersonic flow (Mach 5) and complex flow behavior is observed due to formation of strong aerodynamic shocks and flow stagnation. Smooth separation is one of the critical parameters which governs the trajectory of the penetrator and its successful penetration on the armor. Aerodynamic disturbances imparted during separation, will also decide the accuracy of the penetrator. Therefore, external profile of sabot as well as other parameters such as mass, location of center of gravity, inertial properties etc., are required to be critically considered during design so that the sabots can quickly separate with minimal aerodynamic disturbances imparted to the penetrator. In this study, the sabot separation is carried out using CFD and the results are presented. This can help researchers to understand the sabot separation phenomenon in details, providing insight about the effectiveness of CFD to analyze the critical aspects of sabot separation.
NUMERICAL STUDY ON THE EFFECT OF ROCKET JET ON THE ROLLING MOMENT OF ARTILLERY ROCKETS WITH WRAP AROUND FINS
Tube launched unguided artillery rockets are stabilized in general by canted wrap around fins in order to nullify thrust misalignment and aerodynamic asymmetries. Wrap around fins are located at the rear end of the rocket and are in close proximity of the rocket jet. The effect of rocket jet on the rolling moment generated by the wrap around fins is studied for the powered phase using ANSYS Fluent CFD simulation. External flow over the rocket and internal flow through the rocket nozzle are simulated simultaneously in order to capture the effect of rocket jet on rolling moment generated by the fins. External flow is simulated for subsonic as well as supersonic Mach numbers. Results clearly show that presence of jet alters the rolling moment only for the subsonic external flow. The rolling moment for subsonic external flow has a higher magnitude in the presence of rocket jet.
DESIGNING THE ROLL CHARACTERISTICS & PITCH-ROLL LOCK-IN OF AN UNGUIDED ARTILLERY ROCKET BY TAILORING THE CHAMFER ON FINS
The effect of the fin leading edge and trailing edge chamfers on the roll characteristics of an artillery rocket is studied. Computational fluid dynamics (CFD) simulations suggested a very high dependency of the rolling moment in the subsonic and transonic regime on the trailing edge chamfer while the leading edge chamfer dictates the rolling moment in the supersonic regime. Six degree-of-freedom trajectory simulations were carried out to estimate the roll frequency in flight and the separation of it from the pitch/yaw frequency. It showed that in certain configurations pitch/yaw and roll lock-in took place which could have hampered the flight stability. This strong sensitivity of the rolling moment to the fin chamfer, even with the fin sizing and the cant angle kept constant, can make or break the flight stability of the rocket.
MAGNUS EFFECT OF YAWING-SPINNING TARGET PRACTICE PROJECTILES: GYROSCOPIC AND DYNAMIC INSTABILITIES IN SUPERSONIC FLIGHT
Despite extensive studies, mechanisms governing the aeroballistics of yawing and spinning projectiles are still difficult to understand. This is especially true for target practice projectiles settled with additional roll damping devices. The first part of the paper is devoted to the aerodynamic comparison of classical and target practice projectiles. For classical projectiles it is known that, at small angles of attack, the spin induces a weak asymmetry of the boundary layer profiles. For target practice projectiles, the roll damping devices, settled as longitudinal grooves, could generate important modifications of the flow. Grooves act on the boundary layer asymmetry, strongly increasing the Magnus moment. The second part of the paper, based on 6 degrees of freedom computations, is devoted to the prediction of flight dynamic behavior. According to the grooves design, dynamic and gyroscopic instabilities could appear. The influence of grooves depth on the inflight behavior is highlighted.
EFFECT OF BOURRELET LENGTH ON MAGNUS MOMENTS AND FLIGHT STABILITY OF THE PROJECTILE
Aerodynamic design of an artillery shell often presents a challenging situation for the designer. Design parameters which enhance in-bore performance of shell in terms of reduced balloting & acceptable yaw rates at the muzzle end, in-turn disturbs the in-flight stability in certain flight regime. Similarly, design parameters which enhances in-flight static & dynamic stability, adversely affect the motion of shell inside barrel. Hence, an optimal selection of values of each design parameter is mandatory to attain desired performance of the ammunition both outside and inside the barrel. One of such design parameters is the Bourrelet distance or wheelbase, which is considered for this study. Parametric studies to evaluate comparative aerodynamic performance of artillery shell with varying bourrelet distance in terms of four major performance parameters such as Muzzle Jump Factor (MJF), Drag characteristics, Gyroscopic Stability & Dynamic Stability are carried out using commercially available software, PRODAS Version 3.2. Out of these four parameters, only MJF & Dynamic stability parameters are analysed in detail in the present work. Comparative values of MJF are used to evaluate inbore stability in terms of initial yaw rate at muzzle exit. Dynamic stability is evaluated in terms of Magnus moment generated by spinning shell. Effect of Magnus moment in terms of total angle of attack damping response during flight is studied by simulating trajectory of the shell for all firing zones. To study the effect of bourrelet distance on performance parameters, bourrelet distance is varied from 0.6 Cal to 1.4 Cal, where Cal is the maximum
INVESTIGATION OF THE EFFECT OF SURFACE ROUGHNESS ON THE RANGE OF A 155mm BOAT TAIL PROJECTILE
The surface roughness of a 155 mm artillery projectile is a controlled parameter during manufacturing, but not much data exists as to its influence on actual performance. It was decided to use practical empirical calculations as a first-order prediction of its effect on drag complemented with a CFD simulation and verified by actual firings of generic 155 mm BT projectiles with various surface roughness values. Practical empirical correlations for the effect of surface roughness on flat plates for compressible flow were used while the FloEFD solver was used for a CFD prediction of the effect of surface roughness on a standard 155 mm shell. For validation, a group of standard 155 mm projectiles with increasing surface roughness were fired. The drag curves obtained from the radar data showed a continuous increase from the baseline curve as the surface roughness increased, with the overall trend of the dynamic firings corresponding well with the CFD simulation.
UNCERTAINTY: WHAT DOES IT MEAN FOR BALLISTIC CHRONOGRAPHS?
Two of the most cited performance properties of ballistic armour systems that characterize resistance to penetration are the ballistic limit (V50) and the proof velocity (Vproof). It is therefore critical that the test velocities are measured with a high degree of certainty for gaining confidence in the ballistic performance assessment for research and development, demonstration of compliance, and quality control purposes (i.e., ISO 17025). Unfortunately, common ballistic testing standards (NIJ 0101.06, ASTM E3062, etc.) do not provide sufficient clarity regarding contributors to consider, coverage factors, or interpretation of stated accuracy limits, leaving significant room for interpretation. This work applies principles of the Guide to the expression of uncertainty in measurement (GUM) to a COTS ballistic chronograph (SpeedTube™) to form a basis for discussions regarding interpretation of standards and the need for standards to use language consistent with the International Vocabulary of Metrology (VIM) for the benefit of researchers, manufacturers, and test facilities.
FROM BENCH TO SHOOTING RANGE: CORRELATING BASE BLEED CHEMISTRY WITH THE BALLISTIC PERFORMANCE OF EXTENDED RANGE MUNITION
Extended range munitions (ERM) are systems whose performance is subject to aerodynamic, internal ballistics and trajectory effects. There are models in the literature for each of these aspects; thus, a holistic approach that unifies them would—theoretically—be able to predict the performance of an ERM from bench tests. In this work, we propose such approach. From the integration of chemical composition data, bench tests, combustion simulations, aerodynamic simulations and trajectory dynamics simulations, the behavior of a Base Bleed (BB) unit could be satisfactorily estimated. The results obtained suggest that the composition of combustion products plays a key role in the performance of BB systems.
FURTHER EVALUATION OF CRITICAL RICOCHET ANGLES FOR WHA PROJECTILES ON METALLIC TARGETS
Critical ricochet angles of 25 mm APDS-T and APFSDS-T projectiles have been evaluated numerically for a range of steel plate thicknesses. Ricochet is a phenomenon of projectile deflection that may be observed when striking highly oblique targets. Critical ricochet angle is defined here as a transition angle from regime of ricochet to perforation. The critical ricochet angle may depend on material properties of both target and projectile i.e. density, strength, failure, high strain rate properties, geometry, target thickness, projectile L/D ratio, shape, and the impact velocity. This study investigates the effect of thickness and strength of steel plates on critical ricochet angle. In addition, critical ricochet angles of 25 mm medium caliber projectiles were compared. Each armor steel target was impacted at varying angles of incidence until ricochet was observed. We demonstrate that there is an optimal thickness of steel targets against the two types of penetrators. The optimum may be used for armor platforms frontal upper hull design. It is recommended to continue to validate the numerical model results with more experimental data.
BULLET PENETRATION INTO BAMBOO, ORIENTED STRAND BOARD AND LOW-DENSITY FIBREBOARD TARGETS
In previous work, we have discussed projectile penetration experiments into a variety of wooden targets, i.e. natural wood, and medium density fibreboard (MDF) targets. However, this paper will discuss normal projectile impacts on three different types of wood-based materials: bamboo, oriented strand board (OSB) and low-density fibreboard (LDF). Impact experiments have been performed using flat targets. Two different 9 mm projectiles are used: Ball and Ball Subsonic. Penetration depths of projectiles are determined using x-ray photography. The experimental data are analysed using the Poncelet model and the Robins- Euler model. As in previous work on wooden materials, penetration depths of the projectiles are related to physical properties of the target material. For bamboo, OSB, and LDF Janka hardness measurements have been performed. Results obtained are compared with earlier results on MDF and natural wood. Again, the observed dynamic strength R shows a good correlation with the Janka hardness.
EFFECT OF MoO3 CONTENT ON MECHANICAL RESPONSE AND THE ENERGY RELEASE IN METAL/FLUOROPOLYMER COMPOSITE
In recent years, PTFE/Al-based reactive materials with high energy density have attracted wide concern, but the low energy release efficiency restricts further application. In this paper, molybdenum trioxide (MoO3) was introduced into PTFE/Al to control the mechanical response and the energy release performance. With the MoO3 content increasing, the material properties gradually change from elastic-plastic to brittle. The ballistic impact experiments are conducted to analyze the overpressure characteristics of PTFE/Al/MoO3. The experimental results showed that the content of MoO3 has significant influence on the energy release behaviors of PTFE/Al-based reactive materials. With the MoO3 content increasing from 10% to 40%, the quasi-static overpressure peak and impulse decrease from 0.147 MPa to 0.105 MPa, and from 9.184 s · kPa to 5.914 s · kPa, respectively. The mechanism analysis showed that, because of Al/MoO3 reaction characteristics, the additional MoO3 affect the shock wave and impact sensitivity of PTFE/Al/MoO3. The study had constructive significance for the application of oxides to promote the energy release performance of PTFE/Al reactive materials.
EXPERIMENTAL STUDY ON THE SHOCK-INDUCED REACTION CHARACTERISTICS OF PTFE/Al/Bi2O3 REACTIVE MATERIALS
Four PTFE/Al/Bi2O3 ternary reactive materials with different Al contents were prepared by molded sintering method to obtain the influence of Al content on the mechanical properties and impact reaction characteristics of PTFE/Al/Bi2O3 ternary reactive materials, and their mechanical and reaction properties were tested by drop-weight test and the shock induced reaction phenomena were observed by high-speed camera. The results show that the characteristic drop height first decreases and then increases as the Al content increases from 24% to 48%, and the reaction delay time remains unchanged, and the reaction duration first increases and then decreases. When the Al excess is doubled, its reaction is the most intense, the duration is the longest, and the reactivity reaches the strongest. The results of the study can provide some reference for the engineering application of PTFE/Al/Bi2O3
STUDY ON THE PENETRATION DEPTH OF SHAPED CHARGE JETS INTO HIGH STRENGTH CONCRETE TARGETS
The performance of high-strength concrete in jet penetration was investigated in this paper. The penetration results of the two sizes shaped charge jet penetrating four strength concrete tests were compared. The factors affecting the jet's penetration of concrete were analyzed. It was found that the dynamic impedance played a dominant role in weakening the jet penetration ability, whereas the static impedance of the target had little effect on the penetration depth of the jet. The effect of the target strength showed only a very limited improvement in the ability to resist penetration, although its role was gradually manifested with decreasing penetration speed and increasing compressive strength of the target. A revised and concise penetration depth prediction model was established based on the cavity expansion theory and Forrestal equation. The calculation error of the model is very small and it is suitable for concrete of a variety strengths.
EXPERIMENTAL INVESTIGATION ON THE DAMAGE EFFECT TO PARTIALLY FILLED FUEL TANKS BY REACTIVE MATERIAL PROJECTILE IMPACT
To explore the potential of PTFE/Al/W reactive material projectile (RMP) in damaging the partially filled fuel tanks, a series of ballistic experiments have been conducted to investigate the damage effect. The experimental results show that both the impact position and the impact velocity of the RMP have significant influence on the damage behavior. For mechanism consideration, the energy release characteristics of RMP closely related to the impact velocity; meanwhile, the fuel/air mixture layer is more flammable than the liquid fuel, and the impact-induced high-temperature deflagration of RMP can generate enough ignition sources. However, when the fuel tank does not disintegrate under the impact, the stored liquid fuel will not spurt out and mix with the surrounding air, only leading to flash-ignition. The sustained combustion only occurs when the RMP successfully causes the fuel tank to disintegrate.
EXPERIMENTAL AND NUMERICAL STUDY ON EFP PENETRATING UNDERWATER DOUBLE-LAYER TARGETS
In order to investigate the damage efficiency of smart micro torpedo armed with EFP warhead, and to reveal its penetration ability, experiment and simulation of EFP forming and penetrating underwater double-layer targets are carried on. In this paper, influence of the distance between EFP warhead and targets underwater is studied, which covers 0, 40, 120, 200, 280mm depth of water. In addition, a penetrator is exceeded by different kinds of buffer materials. The experiments show that, compared with EFP in the air, EFP formed by underwater weapon results in smaller holes on the double-layer target. With the increase of the depth of water, the projectile loses its mass and velocity and damage diameter of the target remains an approximate constant first and then decreases. Interestingly, the simulation demonstrates a unique damage mechanism different from that in the air, which affected by the penetrator and underwater shock wave
INTERACTION REGIMES FOR HYPERVELOCITY JET AND FLYING PLATE
This paper covers the theoretical and numerical simulation studies performed to investigate the interaction of hypervelocity jet and flying plates. The type of interaction between the jet and the flying plate depends on several variables such as the velocity, thickness, obliquity of the flying plate, and the velocity and diameter of the incoming jet. In this study, four modes of interaction between jet and flyer plate, and necessary conditions for each mode of interaction are proposed, depending on the flyer plate and hypervelocity parameters. Then, these conditions are proved with a simulation study. Simulation results are examined both qualitatively by the deflection of the jet and quantitatively by comparison of momentum transfer on the jet. It is seen that conditions for interaction modes are in agreement with simulation results.
SENSITIVITY STUDY OF X-RAY COMPUTED TOMOGRAPHY FOR EVALUATING THE MASS AND STRIKING VELOCITY OF EMBEDDED FRAGMENTS IN PLYWOOD RECOVERY MEDIA
X-ray computed tomography coupled to the automated data analysis tool FragFinder was used to study six targets impacted by 11 different projectiles. Extracted projectile DOP, volumes, and densities provided a sufficient database for predicting impact velocity. The obtained precision is estimated to be in the range of ± 12 % with similar contributions of projectile density (± 2.2 %) and volume (± 2.8 %). The main observed challenges are the necessary high image resolution for small projectiles combined with the generally large size of recovery media (targets) and the presence of certain metals such as Zr, Mo and Pb in projectiles. Their high atomic number and density are causing CT image artefacts and measurement saturation, even at low concentration levels.
MICROSCALE DEPTH OF PENETRATION AND OBLIQUE IMPACT OF UNIDIRECTIONAL GLASS/EPOXY COMPOSITES
Spacesuits and spacecraft must endure high velocity impacts from micrometeoroids. This work considers the impact of 100 μm diameter projectiles into composite targets at velocities from 0.5 km/s to 2 km/s. This work begins by presenting an energy-based theoretical model relating depth of penetration (DoP) and impact force to impact velocity, characteristic time, and threshold velocity and force. Next, this work compares numerical simulations of normal impact on composites to the theoretical model. Numerical simulations are conducted with LS-DYNA and the well-known composite model, MAT-162. The numerical models consider unidirectional S2-glass fiber reinforced SC-15 epoxy composite laminates. The numerical model shows good correlation with the theoretical model. The numerical model also investigates lateral impact, parallel to the fiber direction, and oblique impact at angles from 30° to 82.5°. This work decomposes oblique impact into normal and lateral components, and compares them with normal and lateral impact results. The results show good correlation of the normal component of oblique results with the theoretical model. This numerical and theoretical study focuses on DoP, velocity, and penetration resistance force as functions of time. The theoretical model and numerical simulations are used to determine new DoP parameters: characteristic time of depth of penetration and threshold impact velocity. These models are a first step in developing the capability to predict DoP for oblique, microscale, high-speed impact on composite materials.
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF TERMINAL BALLISTIC IMPACT OF GELATIN
Knowledge of wound ballistics is essential to protect our warfighters. The presented work achieves this goal by studying impact into 10% ballistic gelatin. Experiments were carried out with steel spheres for three different velocities. Decay curves are recorded to give the complete picture of this complex event. As the background for numerical modeling of the experiments, a comprehensive literature study was done on this topic, especially related to numerical algorithms, and applied constitutive models for gelatin. The γSPH solver in the IMPETUS Afea Solver Suite is used to model the gelatin utilizing GPU technology for computational efficiency. Power-law plasticity, non-linear elasticity, and simple fluid constitutive models were tested, and results are compared with the experiments. The simple fluid model seems to yield the best results, and in general, all results are within a margin of 10% error.
INVESTIGATE THE PENETRATION CHARACTERISTICS OF A FOLLOWING KINETIC ENERGY PROJECTILE TO CONCRETE WITH A PRE-DRILLED CAVITY
The penetration characteristic of a following kinetic energy projectile to the concrete with a pre-drilled cavity is investigated through the theory and numerical simulations. With the precondition of the equivalent volume of the pre-drilled cavity, the results are compared in terms of the kinetic parameters of the penetration process, the depth of penetration of the following kinetic energy projectile. A theoretical model is then employed to assess the depth of penetration of the following kinetic energy projectile at the condition of variation of the diameter and the depth but the volume of the pre-drilled cavity being invariant. In addition, the numerical simulation is carried out to present the penetration process of the following kinetic energy projectile to the concrete with a pre-drilled cavity. The results show that the existence of the pre-drilled cavity is conducive to increase the depth of penetration of the following kinetic energy projectile on the concrete. In case of the same volume of the pre-drilled cavity, the depth of penetration of the following kinetic energy projectile on concreter increases initially and decreases afterwards with increase of the diameter of the pre-drilled cavity. The theoretical results correlate with the simulation results reasonably well.
A BAYESIAN OPTIMIZATION METHODOLOGY FOR THE INVERSE DERIVATION OF VISCOPLASTICITY MODEL CONSTANTS IN HIGH STRAIN-RATE SIMULATIONS
Inverse strategies, which incorporate numerical simulation of the experiment and iterative adjustment of model constants until measured signals can be numerically reproduced, are widely employed in finite element modelling, e.g., Finite Element Model Updating (FEMU) [1], Constitutive Equation Gap Method [2], etc. These strategies permit the utilisation of more extensive data than classically used, e.g., digital image correlation (DIC) for surface strain. Such inverse strategies are typically employed on thermomechanical tests, however a limited number of studies have investigated these methods applied to functional experiments, that is experiments which have utility beyond the derivation of constitutive model constants. For example, Walls et al. [3] performed inverse modelling to optimise constants of energetic materials cylinder test and wedge test. Portone et al. [4] performed model identification and tuning of existing model constants based on inverse modelling of a penetration vs. time experiment. These approaches, however, may result in model constants which are not generalisable – that is, for experimental conditions different to those used in the inverse approach, the identified constants will be inaccurate. Here we present a methodology for deriving constitutive model constants for use in explicit finite element simulations of dynamic processes from multiple functional experiments. The resulting model should be better able to generalise to previously unseen conditions, provided that those conditions are within the range bounded by the initial experiments used for the optimisation. We demonstrate the optimisation methodology using high hardness armour steels across three types of experiments that induce a wide range of loading condition: ballistic depth of penetration [5], rod-on-anvil [6], and near-field blast deformation [7]. We employ an inverse methodology in which (1) a random initial guess of material constitutive model parameter is made (for a predefined constitutive model), x0, (2) simulations of the functional experiments defined above are conducted in LS-DYNA with the selected constitutive model and model constants, and (3) the simulation results are compared with the experimental measurements to determine the total simulation error. An optimisation function is tasked with modifying the model constants and repeating this process until a minimum error is obtained, from which the optimal constitutive model constants can be identified. As hydrocode simulations are computationally expensive, we utilise Bayesian optimization (BO), one of the most sample efficient optimisation techniques available, for this task. We perform an initial optimisation to select a plasticity model from: Zerilli- Armstrong, Johnson-Cook, and two modifications of the Johnson-Cook model. The best performing option, a modified Johnson-Cook model (MJC), is then subject to a more comprehensive optimisation process utilising a leave-one-out (LOO) methodology to maximise the generalisability of the identified solution. In multiple runs of the optimisation the best identified MJC constants do not exhibit any obvious clustering, suggesting that the solution is non-unique, i.e., there are a range of hyperparameter combinations that can generate comparable results in LS-DYNA. This is not unexpected as the constants of the MJC model are not independent - for instance the strain hardening response can be well defined by varying subsets of its empirical constants. A comparison of the dynamic stress-strain response described by the different constantsidentified in each optimisation run are plotted in Figure 1, together with examples of thesimulated experimental results. For comparison, baseline results are also plotted which utilise constitutive models and constants derived from conventional mechanical characterisation experiments or alternative optimisation approaches. To evaluate the generalisability of the optimised MJC constants we simulate a new experimental condition not included in the optimisation process - dynamic compression with a split Hopkinson pressure bar (SHPB) apparatus from [6][8]. The best simulation results utilising the BO-identified constitutive model constants were found to provide comparable results to the baseline model derived specifically from these experiments, and superior results compared to other baseline models, confirming the generalisability of the derived model constants.
BALLISTIC PERFORMANCE OF ADHESIVELY BONDED JOINTS
In this study, ballistic performance of adhesively-bonded Single Lap Joints is investigated experimentally and numerically. Using a specially-designed experimental set-up, a projectile with mass of 1.25 gr and density of 11.3 gr/cm3 was fired to the joints at a velocity of 288 m/s. The joints with a thickness of 4 mm and two different overlap lengths, 15 mm and 25 mm, were first subjected to the ballistic and then to the quasi-static tensile tests. When the impacted joints were compared to the non-impacted ones, it was found that while the joints with the 15 mm overlap length mechanically deteriorated, those with the 25 mm length were not affected. These results were validated numerically via the ABAQUS package program. Johnson Cook behaviors of the materials were used as input data in the analysis.
THE INFLUENCE OF PREFORMED HOLES ON THE DYNAMIC RESPONSE OF BLAST LOADED ALUMINUM PLATES
In this paper, the dynamic response of Aluminum plates with predrilled holes subjected to different intensities of blast loading is studied both experimentally and numerically as to imitate the case where fragments strike and perforate the plates before the load pressure arrives. The blast loading is applied using an Explosive Driven Shock Tube (EDST) [10-12] which ensures a uniformly distributed blast wave on the test specimens. Experiments were carried out for different sizes, positions, and numbers of the predrilled holes in the plates positioned at the end extremity of the tube. Special focus is dedicated to investigate the influence of these parameters on the dynamic response and failure characteristics of plates via the Digital Image Correlation technique (DIC). Numerical simulations were performed in the finite element code LS-DYNA to recreate the plate deformation and the observed phenomena seen in the experiments.
STUDY ON IMPACT INDUCED FRAGMENTATION OF W/Zr ALLOY
In this paper, the static and dynamic mechanical properties of tungsten-zirconium alloy and the impact crushing law of the material were studied, and the fracture morphology of the recovered samples was observed under scanning electron microscope. The true stress-strain curves under static and dynamic conditions were obtained by quasi-static compression experiment and split Hopkinson pressure bar experiment. It was found that the increase of tungsten content would decrease the plasticity and increase the yield strength of the material. The relationship between the residual mass of tungstenzirconium alloys and the size of the fragments under the impact velocity was obtained by Taylor impact experiment. It was found that the power law distribution theory for brittle materials could also describe the impact fragmentation of binary tungsten-zirconium alloys with non-brittle properties.
NUMERICAL ANALYSIS OF THE DYNAMIC MECHANICAL BEHAVIOR OF HIGH STRENGTH ALUMINUM ALLOY AA2014-T652 UNDER HIGH IMPACT VELOCITY
The present paper deals with the numerical analysis of the impact and perforation of a high velocity rigid steel spherical projectile through an Aluminum plate AA2014-T652 using the commercial software LS-DYNA. These numerical investigations are performed in the velocity range from 800 m/s to 1300 m/s. The target plate with a thickness of 15mm and the spherical projectile with a diameter of 10mm are modelled using three-dimensional elements (3D) in a Lagrangian formulation. A hydrostatic tensile stress failure model combined with the Johnson and Cook constitutive model is used to highlight the dynamic failure of the target. The different failure mechanisms observed on the Aluminum plate from the moment of impact to full perforation are discussed. The numerical results based on the crater diameter at the front and rear surface of the plate and the dimensions of the penetration channel are compared to the experimental data available in literature.
METHODOLOGY TO SELECT ROD PARAMETERS FOR MAXIMIZING DAMAGE AT HYPERVELOCITY IMPACT
Damage assessment is essential when a threat missile payload is intercepted by a missile carrying high explosive warhead. In near miss condition, projectiles (i.e. rods, pellets or fragments) deployed by the warhead impact on a threat missile. Selecting a rod parameter is a challenging task as its effectiveness depends on impact conditions, which varies with various engagement scenarios. Extent of damage depends on target specifications, impact conditions and rod parameters. To resolve this challenge, first simulations are validated for a few experimental data. Using validated simulation model, the data is generated regarding extent of damage caused by changing rod parameters for a set of impact conditions. Then, a methodology to select optimum rod parameter is worked out. Wherein, artificial neural networks (ANN) are built using the discrete set of simulation data and then based on probability of impact conditions, Monte Carlo simulations are performed to obtain probability of successful damage cases. The proposed methodology helps in selecting an optimum rod for the given range of impact conditions.
INVESTIGATION ON IMPACT INDUCED ENERGY RELEASE OF PYROPHORIC ALLOY FRAGMENTS USING TIME RESOLVED EMISSION SPECTROSCOPY
Technical advancement in material production open new doors in developing reactive material (RM) compounds that combine structural strength with exothermal energetic characteristics. Utilized to exchange inert materials, such as warhead shells, RM enhance the lethal effects. The warhead is initiated, its RM shrapnel accelerated and impact the secondary targets. Upon impact, an impact induced energy release (IIER) occurs in form of exothermal chemical reaction of the RM on the target material. For a repeatable and comparable results, a dedicated experimental set-up has been developed where single cylindrical RM fragments of a diameter D=5 mm and the same length L (L/D=1) represent the shrapnel. They are ballistically driven at initial velocities vi=1500 m/s, using a 7.62 mm powder gun. The RM fragments consists of Ferrocerium, a pyrophoric commercial alloy. Although, Ferrocerium is not primarily a candidate to replace warhead shells, its IIER is academically very suitable for the development of experimental measurement techniques. In order to understand the chemical reaction and quantify the IIER, two parameters are measured, the light emission and the pressure. Time integrated and time-resolved emission spectra, obtained by a Czerny-Turner spectrograph are discussed in this paper. From the investigated wavelength of the oxidation of lanthanum, a predominant compound of the Ferrocerium RM, temperature can be derived between 2300° and 3000° C. In addition, the RM fragment is launched in a closed chamber with pressure sensors and a pressure measurement is taken simultaneously with the light emission. In order to protect against RM enhanced weaponry, the effects of IIER need to be understood.
ANALYSIS OF INTERFACIAL PRESSURE OF Zr-BASED METALLIC GLASS FRAGMENTS IMPACTING TARGET
In the present paper, the process of Zr-based metallic glass fragments impacting the target plate is analyzed by one-dimensional stress wave theory to obtain the interfacial pressure between the target and fragments and other relevant influencing parameters. Meanwhile, combing with jh-2 material constitutive model, simulations were conducted to simulate the process of Zr62.5Nb3Cu14.5Ni14Al6 impacting the target plate at the speed of 600m/s-1500m/s with ls-dyna 3d software. The effects of fragments on the process of impacting target plate at different initial velocities were analyzed by combining theory and numerical simulation. The accuracy of jh-2 model for simulating Zr-based reactive fragments impacting steel target at low speed is verified, which can provide a reference for the calculation of reaction threshold of reactive fragments impacting steel target.
FIRST-PRINCIPLES INVESTIGATION OF IMPACT-INDUCED OXIDATION OF REACTIVE MATERIALS
The strain-dependent oxidation of metals for reactive material warheads is studied with quantum mechanical simulations. A two-stage surface oxidation process was investigated for Titanium, Copper, and Zirconium in unstrained condition and for isotropic compression and tension. The results show exothermic surface oxidation and an increased strain-sensitivity for the pyrophoric materials Titanium and Zirconium in comparison to non-pyrophoric Copper. While tension stabilizes the surface oxidation, compression leads to a destabilization of oxidized surfaces. The release of metal oxides from the oxidized surface is endothermic for all materials in unstrained condition. It was found that the release of metal oxides is stabilized by compression and can even be turned exothermic by sufficient lattice strain.
THE HIT POINT DEPENDENCE IN THE INTERACTION BETWEEN LONG ROD PROJECTILES AND EXPLOSIVE REACTIVE ARMOUR
Long rod projectiles interacting with explosive reactive armour consisting of two flyer plates sandwiched around a high-explosive material is studied numerically and experimentally to understand the influence of hit point on the fracture and deformation behaviour of the projectile. The results shows that fracture, deformation and consumption of the projectile occurs mainly due to interaction with the plate moving in the same direction as the projectile. As the time span of this interaction is sensitive to the hit point, the hit point dependence should be taken into account when considering using explosive reactive armour as protection.
RESPONSE OF BRICK MASONRY WALLS TO RPG-7 THREAT
The paper deals with the problem of RPG-7 (rocket propelled grenade) impact on the brick wall with SLAT armour. The scenario when the warhead is deactivated on SLAT armour, continue to move with some reduced velocity and interact with brick masonry wall is solved. The detonation of the explosive without jet formation is also considered. Experimental and numerical study of the brick masonry walls interaction with such was performed. Unreinforced walls and walls reinforced by using of steel add-on plates have been tested. Numerical simulations were carried out to estimate the response and damage of reinforced and unreinforced brick masonry walls subjected to RPG-7 threat based on the transient dynamic finite element program LSDYNA. The numerical simulation was used for the evaluation of the effect of the steel add-on plate thickness on the ballistic resistance of the masonry wall to the RPG -7 threat.
THERMAL ENERGY ANALYSIS OF PROJECTILES DURING RICOCHETING USING A THERMAL CAMERA
This paper presents the results of a study of the hazards of ground ignition and/or explosion when various small-calibre projectiles strike various solid materials placed on a test stand in environments at risk of ignition (fire) or explosion (ricochets, projectile penetration of obstacles). For projectile ricocheting tests, the following were used: armour plate, concrete, sidewalk and granite slabs, etc., and various small-calibre projectiles. Projectiles impacts were recorded with a high-speed camera and thermal camera. The ignition capability of solid flammable materials during projectile ricocheting was studied, and the temperatures and surface areas of isotherms were measured as a function of time. From the spherical distribution of thermal energy radiation in space, their volume, mass of air occupying the studied area, masses of projectile disintegrating into fragments (after impact), thermal energy during projectile ricocheting, histograms of area temperatures, temperature, were calculated.
RESEARCH ON DISTRIBUTION OF BEHIND-ARMOR DEBRIS FROM PENETRATION OF TARGET BY EFP WITH DIFFERENT LENGTH-DIAMETER RATIO
To research the distribution of behind-armor debris (BAD) of explosively formed penetrator (EFP) more comprehensively, three EFPs with different length-diameter ratio (L/D) were designed, and experimental study on the dispersion characteristics of BAD from EFP penetrating 45# steel target was carried out. The morphology and scattering characteristics of debris cloud after EFP penetrating steel target were observed by X-ray photography and high-speed photography, and BAD were recovered by the method of stacking fiber plates and polystyrene plates. The mass spatial distribution law of projectile material and target material fragments was obtained. Results indicate that the increase in EFP L/D has a greater increase on the normalized axial expansion velocity of debris cloud than the radial expansion velocity. The average mass and perforation area of fragment corresponding to the relative accumulation value of 1/2 both decrease with the increase of the EFP L/D. The increase of EFP L/D mainly enhances the concentration of the EFP fragment mass towards the residual penetrator axis, but has little effect on the target fragment mass, which is basically uniformly distributed along the scattering angle.
MESOSCALE STUDY ON THE DYNAMIC MECHANICAL BEHAVIORS OF Al-PTFE-W REACTIVE MATERIALS
Mesoscale simulations were conducted to investigate the dynamic mechanical behavior of Al-PTFE-W reactive materials. Based on stress-strain curves and microstructural evolution of the materials, the dynamic response mechanism of the materials was revealed, and the effects of W content and temperature on the dynamic mechanical properties of the materials were analyzed. The results demonstrate that the failure of the materials is a process of damage accumulation, in which microvoids generate and develop to form cracks. Two forms, dislocation between metal particles in contact as well as matrix fracture due to extrusion or shearing of metal particles on either side, induce the microvoids. Addition of W with high strength improves the compressive resistance of the materials, but excessive W particles destroy the continuity of matrix, which is easy to cause premature failure of the materials. The thermal effect simultaneously reduces the strength of metal particles and matrix, thus reducing the compressive resistance of the materials and promoting the matrix cracking.
PERFORMANCE OF A TANTALUM FOR APPLICATIONS OF EXPLOSIVELY FORMED PROJECTILES
The deformation rate of explosively formed projectiles (EFPs) are extremely high, at the strain rate orders of more than a half million strain per second. The deformation occurs often at the magnitude of several hundred percent of strain, and the adiabatic heat is considerable. Challenges for developing a material model suitable for simulations of the projectile lies in the limitation of material testing where the strain rates used often are several orders of magnitude lower than what occurs in EFP projectiles. In this work, an effort is made to establish a dislocation thermal dynamics based model for a batch of tantalum to characterise its material behaviour at extreme strain rate, magnitude, and temperature, based on conventional material test results for both room and elevated temperatures at moderate strain rates. The validation of numerical simulations with this model for the EFP test results shows that there is a potential with the theoretical model based on the dislocation movement for such applications.
EXPERIMENTAL VALIDATION OF A NUMERICAL MODEL OF THE 7.62 x 39 M43 PROJECTILE
Both in military and in law enforcement operations, the most commonly found small caliber threat is the ubiquitous Kalashnikov, also known as the AK-47 (or simply AK). For that reason, a detailed experimental and numerical study of the 7.62 x 39 M43 projectile was made. In this work, 7.62 x 39 mm mild steel core ammunition was fired against a rigid wall, made of a high-hardness steel plate of sufficient hardness and thickness to respectively avoid denting and bulging, to characterize the projectile core deformation and damage as a function of impact velocity. The validated projectile finite element model can now be used to study more complex impact problems where experimental measurements are complex or impossible. A good qualitative and quantitative correlation between numerical and experimental results for the considered ammunition was achieved.
BALLISTIC LIMIT RESEARCH OF REACTIVE PROJECTILE IMPACTING THIN ALUMINUM PLATE
There exists a ballistic limit velocity when projectile impact on plate, which is a widely recognized terminal effect of projectiles in previous studies. However, it is often difficult to analyze the impact process of the reactive projectile on the plate. Its complexity lies in the fact that the process of the reactive projectile penetrating the plate depends not only on its kinetic energy, but also on the chemical energy released by the reactive material under strong transient load. In this paper, Ballistic limit behavior of reactive projectile impacting thin aluminum plate was studied, ANSYS/LSDYNA was used to obtain the ballistic limit of reactive projectile impacting thin aluminum plate. Meanwhile, based on the critical stress/strain rate activation hypothesis of reactive materials, the ballistic limit of reactive projectile is analyzed by one-dimensional shock wave theory. The simulation results are in good agreement with the theoretical calculation.
INFLUENCE OF THE PENETRATOR MATERIAL ON THE DEPTH OF PENETRATION OF TUNGSTEN ALLOY APFSDS PROJECTILES IN AA 7020 T651
Experimental and numerical investigations of the penetration of APFSDS projectiles in semi-infinite targets of Mars® 380 and AA 7020 T651 are presented in this work. Two different tungsten heavy alloy penetrator materials with different strengths have been used. In armor steel the material of the penetrator was found to have only a minor influence on the depth of penetration. In the AA 7020 T651 targets the influence of the penetrators strength was found to be important, especially as at lower velocities the penetration process does not lead to an erosion of the projectile. With the numerical simulation the deforming penetration process could be reproduced, but more effort is necessary to evaluate a reliable strength model parameter set.
REVIEW OF TERMINAL BALLISTICS OF A BULLET IN THE HUMAN BODY
The terminal ballistics of a projectile in the human body are reviewed, both the theory, experimental data, and their implications for medical/surgical treatment. The focus of the past century has been to increase the kinetic energy of the bullet but ignoring the material from which the bullet, firing chamber, and target are made. The more efficient delivery of this kinetic energy to the target is proportional to the damage caused. The bullet causes a tract through the impacted tissues that is related to the size of the projectile, but the accompanying shock wave causes a much larger temporary cavity which, depending on the structure and elasticity of the tissue, will stay patent for only 2-4ï­sec. Surgical resection of the permanent tract containing injured tissue, bullet fragments, and contaminated material is initially performed followed by the repair of the tissues injured by the bullet.
ENHANCED DAMAGE EFFECT OF REACTIVE FRAGMENTS OBLIQUE PENETRATING TITANIUM ALLOY PLATES
Focusing on the reactive fragments oblique penetration behavior, a series of penetration experiments at velocity of 630-1040m/s at 0-60°were conducted. The results show that the area of perforation hole at 30° increase 143.53% compared with that of normal penetrations, ricochet occurs at 60°. The perforation size at critical velocity (v =705m/s) is much larger than that at higher velocity (v=734m/s) when both oblique penetrated at 30°. The damage zone of front titanium alloy plate was divided into 5 zones according to the morphology of damaged plate. The analytical mode considers both kinetic energy and chemical energy of reactive fragment is developed to reveal the mechanism of enhanced damage effect of reactive fragment oblique penetrating at critical velocity.
BALLISTIC TESTS OF BULLET IMPACT INTO WATER
Research works described in the paper, were performed within the framework of the project: Laboratory stand for stopping high-energy projectiles (Agreement no. DOBBIO10/ 04/02/2019). Methods used nowadays in forensic laboratories allow to stop some kinds of projectiles with degree of deformation which lets to use them for comparing traces to bullets found on the crime scene. However they are not useful for every type of projectiles. The aim of the research is to elaborate methods which allow to slow down and gently stop high-energy susceptible to deformation bullets in a way that does not cause their deformation or possibly limit it. The paper presents the results of ballistic tests of impact of various types of projectiles into water. The behavior of bullets of various calibers, with different kinetic energy and different construction was analyzed. On the basis of the obtained results, the projectiles with the highest susceptibility to deformation were identified.
DATA ON DECELERATION HISTORY OF BODY IN RHEOLOGICAL MEDIUM AS A BASIS FOR VERIFY OF TERMINAL BALLISTICS CALCULATED TASKS
The reports materials on the data presented by the authors earlier in the proceedings of 23rd- 31st International Symposiums on Ballistics are base. The results relate to the field of study of the action of the body on the target. Measuring technology is a set of methodological, technological and software components for tests measuring strikers-probes. Such strikers are equipped with impact accelerometers and original systems for connect with recorder. The difference from the known methods is the realizable range of impact velocities: 100 - 2500 m/s at the stage of action on the target. Theoretical and experimental studies have revealed a new law of medium resistance to penetration. The law allows the application of engineering methods for solving problems. It became possible to solve spatial tasks of penetration with the use of this law.
CATEGORIZING BALLISTIC PERFORATION MECHANISMS OF DUCTILE METALLIC PLATES USING DIMENSIONLESS PARAMETERS
In this work, two dimensionless parameters were derived organically from impact mechanics equations to remove the need for empirical constants. These two dimensionless parameters effectively collapse the ballistic performance of ductile metal plates along two distinct loci, depending on the projectile geometry and the corresponding failure mode. Projectiles that initiate ductile hole enlargement via cavity expansion fall along a linear curve, while shear-plugging failure modes tend to fall along a cubic curve. Results were demonstrated for various projectiles of different calibers impacting aluminum and Ti-6Al- 4V alloys. The main advantage of the approach in this work is to drastically reduce the number of features for input into machine learning algorithms.
THE ROLE OF TANGENTIAL VELOCITY IN EXPLOSIVE INITIATION BY FRAGMENT IMPACT
An initiation study is presented in which we examine the effect of the normal and the tangential velocity components of a fragment that impacts a covered and a bare Comp-B explosive. The study is based on calibrated numerical Lagrangian simulations using the LS-Dyna hydrocode. The influence of the fragment strength and the steel cover thickness on the detonation threshold were also examined, for different impact angles. The velocity threshold results are presented and compared to a modified Jacobs-Roslund initiation model, obtained by substituting the orientation angle by the impact angle. Up to a certain impact angle value the modification appears to fit the results of the simulations.
DYNAMIC POLYMERIC FOAM EVALUATION TO MINIMIZE BEHIND ARMOR BLUNT TRAUMA (BABT): FROM MATERIAL CHARACTERIZATION TO SIMULATION VALIDATION
This paper deals with the characterization of the dynamic behavior and the damping capability of a polymeric foam that is implemented on soldiers’ chest. Split Hopkinson Pressure Bars (SHPB) experiments have been performed at strain rates ranging from 420 to 5100 s-1. The effect of confinement on the deviatoric behavior of the material has been investigated through unconfined and confined experiments. The damping behavior was studied with the help of ballistic tests. Steel spheres were launched on the foam with an aluminum reference backing. 3D Digital Image Correlation (DIC) with two high speed cameras was set up to monitor the back-face deformation and evaluate the dynamic damping capability of the polymeric foam. At the end, a material model was calibrated using the results of the SHPB experiments and the simulation of the ballistic tests showed a very correction with the impact experiment
IMPACT TESTS WITH SINGLE OR MULTI IMPACTORS USING A GAS GUN TO REPRODUCE IEDs’ AND UNCOMMON THREAT
This paper deals with the ability to launch single impactor, sometimes with controlled angles, or synchronized multi-fragments using guns so as to reproduce Improvised Explosive Devices (IEDS) threats. This is done for a wide range of materials from aluminum and steel (light weight tactical wheel vehicle or fragments in detonation chamber [1]) to tungsten heavy alloys (rear face of heavy vehicle, hypervelocity events or hydrodynamic experiments [2][3]). Velocities spectrum is relatively large and englobes aeronautical subsonic regime (<300m/s), common ballistic regime (300-1400m/s) or warheads and hypervelocity regimes (>1400m/s).
APPLICATION OF THE BUILDING BLOCK APPROACH (BBA) FOR LIGHT WEIGHT PERSONAL ARMOUR MATERIALS CALIBRATION
This paper presents a lightweight armor structure calibration method. The armor consists of a stacking of two materials: a ceramic tile and a backing made of UHMWPE (Ultra High Molecular Weight Polyethylene) plate. Using a building block approach, each material is characterized separately before studying the response of the resulted structure under ballistic impact. For the ceramic material, Hugoniot and spall parameters are identified using plate impact tests. Then, data from dynamic confined compression tests on SHPB (Split Hopkinson Pressure Bars) are used to complete the model. The characterization of the composite backing is realized using a dynamic press (tension), SHPB (out-of-plane compression) and gas gun (out-of-plane shear). The out-of-plane shear configuration test has been specifically designed to highlight the behavior of the composite material. Experimental data are used to calibrate a non-linear orthotropic material model with damage for the composite plate and a JH-2 material model for the ceramic. Moreover, the modelling of inter-ply interaction appears to be predominant to correctly reproduce the ballistic behavior of UHMWPE. The model of each material has been validated in a ballistic test configuration using a sphere for the composite and a rod projectile for the ceramic. Additional tests were conducted to study the ballistic response of the stacking (ceramic tile + UHMWPE) with a more realistic 7.62mm projectile
CONCRETE CHARACTERIZATION FOR BALLISTIC THREAT
This ongoing study aims at building a robust approach for reliable simulation of concrete behavior under ballistic impact of Kinetic Energy Penetrator (KEP) from concrete characterization to penetration efficiency. The Holmquist-Johnson-Cook concrete (JHC) material model is used combined with advanced capabilities of γ-SPH formulation available in IMPETUS AFEATM software. A common concrete used in building industry is considered for the study (~35MPa compressive strength). To limit the number of tests, only the most relevant data regarding the penetration phenomena have been investigated: quasi-static compression and dynamic oedometric compression tests have been realized. The impact test is conducted on a confined concrete cylinder at hypersonic speed. The test is instrumented to evaluate the model prediction in terms of projectile deceleration and depth of penetration. The numerical simulation results are in good correlation with the tests and higher impact speed up to 900 m/s will be investigated soon.
APPLICATION OF A BUILDING BLOCK APPROACH (BBA) FOR A HIGH STRENGTH STEEL TRIAXIALITY DEPENDENT STRENGTH MODEL CALIBRATION: FROM DATA COLLECTION TO MODEL VALIDATION
This paper details a Building Block Approach (BBA) methodology developed to fit a material model for a High Strength Steel (HSS) faced to blast/ballistic events. This model includes mesh sensitivity, strain rate influence and triaxiality effect on plastic failure. Data collection in different loading conditions in quasi-static and dynamic regimes has been done. A unique set of parameters have been found by an optimization loop that combines both characterization tests and associated numerical simulations. Validation tests on large square clamped plates at two velocities have been performed in different triaxiality conditions using three nose shapes (flat, hemispheric and conical) to confirm the optimized set of parameters at failure initiation and with perforation. Final numerical simulation of the validation tests showed that the final set of parameters brings a very good agreement: less than 5% discrepancy on remaining kinetic energies.
MESOSCALE AND CONTINUUM MODELING OF BALLISTIC IMPACT ON KEVLAR/PHENOLIC COMPOSITE PLATES
A woven aramid (Kevlar®)/polyvinyl butyral phenolic composite used in ballistic applications was subjected to ballistic impact tests involving various projectile masses and target panel thicknesses. Two different models were generated to simulate the impact tests. The first model is a mesoscale model in which fibers, the surrounding matrix, and interfaces are represented with separate finite elements and material models. The second model utilizes a continuum-level user material subroutine that utilizes rules of mixtures to relate stresses and strains within the fiber and matrix constituents. Simulations of the ballistic tests were conducted using both the mesoscale and continuum models, and the results were compared to velocity and backface deflection data from the tests. The simulation results suggested that the relatively large void content of the material (~11%) has a significant effect on the resulting impact response.
ADAPTIVE EXPERIMENTAL OPTIMISATION FOR SAMPLE-EFFICIENT ARMOUR DESIGN
We present a Bayesian optimisation methodology intended to support a human expert in the design of armour systems for which limited prior knowledge/data exists and within a limiting, pre-defined experimental budget. We apply the methodology to design an armour configuration consisting of multiple plates, with multiple materials, at varying orientations and spacing, for protection against 12.7 mm APM2 and 20 mm FSP threats. The full-factorial design matrix for the defined solution space exceeds 17,500 possible solutions. With an objective to minimise system weight, we identify a solution within 102 ballistic tests (44 design iterations) that provides a weight reduction of 11.4% over expert-designed reference configurations and a mass efficiency of 1.5 relative to a monolithic RHA Class 1. The value of the demonstrated methodology is expected to increase with increasing armour (or threat) complexity.
RESIDUAL PERFORMANCE EVALUATION OF SHAPED CHARGES INITIATED BY ACTIVE PROTECTION SYSTEMS
An approach for the determination of the residual penetration capability of highly disturbed shaped charge jets at large standoff distances was developed. Thereby, the shaped charge detonation is simulated in a hydrocode and the terminal ballistics are assessed in an analytical code. The algorithm for the export of the jet characteristics from a hydrocode simulation is described and the reconstruction of the jets and fragments in the analytical code is explained in detail. Further, an application example is provided that shows the fundamental necessity of the investigation of the problem at hand and that highlights the effective operation of the presented method.
FLIGHT AND PENETRATION BEHAVIORS OF TANDEM EFPS WITH FINS
Based on the principle of kinematic similarity and stabilization storage of a projectile, the flight stability characteristic of a tandem explosively formed projectile (EFP) formed by a shaped charge with double-layer liners and a hexagonal shell was investigated by simulation and theoretical analysis. The damage to multilayer interval steel plates impacted by the tandem EFP with empennages was also studied. Five types of hexagonal shell with representative thicknesses of 0.4, 0.8, 1.2, 1.6, and 2 mm were used. The results show that the hexagon shell has a significant influence on the shock wave propagation direction and time, causing the liners to suffer a periodic impulse and warp regularly at the edge. Finally, the tandem EFP forms three pairs of symmetric fins, which ensure that the EFP flies steadily in the air. The hexagonal shell thickness has an important influence on the formation, flight, and penetration of the tandem EFP. As the hexagonal shell thickness increases gradually, the length:diameter ratios of the tandem EFP decrease correspondingly, and the forerunning and following EFPs have a greater speed difference, causing a larger interval distance as the two EFPs fly steadily in the air. Moreover, the interval distance between the two EFPs plays a crucial role in penetrating the multilayer plates.
BALLISTIC TRADE-OFFS FOR DEPLETED URANIUM REPLACEMENT IN A KINETIC ENERGY PENETRATOR
Depleted uranium (DU) alloys are often employed in kinetic energy penetrators as they show superior terminal ballistic performance over other materials, such as tungsten heavy alloys (WHA). This performance gap is generally attributed to differences in deformation behavior, such as adiabatic shearing in DU alloys. However, due to several factors associated with the use of DU, there is a need to seek a replacement material. The objective of this paper is to identify and model the trade-offs available or required in internal and external ballistics as a function of density of a WHA material such that it would match the modelled terminal performance a DU alloy penetrator. The performance is modelled using the Baer-Frankle lumped parameter model for the internal ballistics, the flat-fire trajectory approximation for the external ballistics and the Walker-Anderson penetration model for the terminal ballistics of a tungsten-like material. The conversion of the deformation behaviour of WHA to a DUlike failure mode is developed from the data of Magness & Farand based on relative crater ratios in the impact velocity range of 800 to 1000 m/s. Modifications, such as the penetrator’s length and a change in propellant, are suggested to define the lower boundaries of density. However, the change to a more energetic propellant would increase barrel erosion rates. With a WHA alloy failing by adiabatic shearing, the minimum required density to match the DU penetrator could be as low as 14.5 g/cm3 but with implications for round stability and an increase in barrel wear rate.
INITIATION CHARACTERISTICS OF COMP-B EXPLOSIVE SUBJECT TO SHAPED CHARGE JET
Under the development of insensitive munitions, the relationship of the diameter - velocity (dj-vj) plane of the jet and the initiation characteristics of explosives under jet impact is studied with conducting numerical simulations. It is found that under the action of jet impact, the initiation point of Comp-B explosive is concentrated at the lower right of the dj-vj plane, and the unexploded point is concentrated at the upper left of the dj-vj plane. There is an obvious boundary between the two domains. The desensitization characteristic of the precursor wave is verified, and it is proved that the vj 2dj criterion is not sufficient. It is also found that there are three different initiation modes of shelled Comp-B with jet impact. One is the impact initiation when the jet begins to penetrate the explosive, the other is the penetration initiation during jet penetration, and the third is the reflection wave initiation caused by the reflection enhancement of bow wave on the exit wall before shooting out of the target. With the increase of the barrier thickness, the three initiation modes change sequentially. Only impact initiation occurred in bare Comp-B and the gap shelled Comp-B.
MESOSCALE MODELING OF BALLISTIC IMPACT ON PLAIN WEAVE COMPOSITE
The goal of this work is to study energy absorbing mechanisms of plain weave composites. Experiments were conducted of 17-grain fragment simulating projectiles impacting singlelayer plain weave S-2 glass/epoxy composites. The focus of the experiments was on determining the ballistic limit velocity. A mesoscale finite element model was developed that includes woven fabric architecture. The mesoscale model includes tow-tow delamination modeled with the cohesive zone model using traction-separation laws determined from finite element models of cracking in fiber-matrix microstructure. The mesoscale model predicted ballistic limit velocity with 1% error. In contrast, a continuum model with effective plain weave properties predicted limit velocity with 6% error. The mesoscale model includes additional energy dissipation mechanisms such as tow-tow delamination, tow pullout, and frictional sliding, which are investigated. Finally, the single-layer model was extended to multi-layer composite penetration, and the impact versus residual velocities were compared with experimental results from the literature.
A METHOD FOR DIGITALLY RECONSTRUCTING PROJECTILE FRAGMENTATION PATTERNS IN GELATIN BLOCKS THAT REQUIRES MINIMAL DATA COLLECTION
The purpose of this paper is to propose a method for constructing a three-dimensional (3D) digital representation of projectile fragmentation patterns in gelatin blocks that requires minimal data collection. The data points required are the start and end points of each fragment’s wound track, as well as the track level designations (a means of organizing how the wound tracks are connected). The maximum likelihood estimates for the parameters of the wound track models are then used to determine the “best fitâ€ fragmentation pattern. Though this paper focuses on the application to gelatin fragmentation patterns, the methodology can be readily used for any visco-elastic material.
BACK FACE SIGNATURE ERROR FOR BODY ARMOR SOLUTION THAT COMBINES HIGH FLEXIBILITY WITH SUPERIOR BALLISTIC PROTECTION—EXPERIMENT DATA VS SIMULATION
The continuous enhancement of weapons with the progress of science and technology required the constant development of protective materials and structures. The most widely applied protective materials are currently ceramic composites, which use ceramic as front plates and other materials as the back plate. Personal body armor is one of important equipment designed to protect human beings from various critical injuries. The severity of such injury is determined by velocity, caliber and weight of the projectile. Back face signature is the result of the energy exchange between the impacting projectile and the human body. The current paper aims to critically review back face signature error between experiment data and numerical simulation for body armor plate consisting of hexagonal shaped SiC Pieces of 10mm thickness and Dyneema SB115 of 15mm thickness against 7.62x39mm “API BZâ€ threat. Main results of this research indicated that back face signature values are similar in both experiment data & numerical simulation with 8% error percentage.
HYDROCODE SIMULATIONS OF HYPERVELOCITY IMPACTS ON A DUCTILE IRON
To prepare for two NASA missions, Southwest Research Institute has been performing both laboratory tests and hydrocode computations of impacts at velocities between 2 and 5.5 km/s on rocks like pumice, sandstone, hematite, concrete, and on metals like aluminum and pure iron (ARMCO iron). All the targets were mounted on pendulums so that the momentum imparted by the projectile to the target could be measured. Note that, in general, the momentum acquired by the target after the impact is larger than the momentum of the projectile. This is due to the additional momentum from the ejecta that flies off the target in the opposite direction to the direction of the impact. Hydrocode computations with CTH and EPIC followed the experiments. This paper will present the laboratory results specifically on ARMCO iron, a material considered a “benchmarkâ€, and the strength and weaknesses of the computations performed.
SIZE SCALING OF FAILURE PROCESSES IN IMPACT
When a high speed or hypervelocity impact occurs, a crater is formed. Size scaling of this event is of interest, meaning, for example, how the crater properties change as the projectile size increases. While penetration depth normalized by projectile radius is fairly insensitive to projectile size, there are other aspects of the cratering process that are quite sensitive to the size of the projectile, including mass of material liberated as ejecta and the amount of momentum that ejecta material has. It is show that there is reasonably good understanding of ejecta mass, but momentum enhancement is still a challenging topic, which we show through experimental results with two aluminums. We also discuss the same effects in concrete targets and the possibility of obtaining more understanding of the size scaling process with the upcoming DART impact into an asteroid.
THE BROWNIAN BASED APPROACH APPLIED TO A LIMITED SAMPLE SIZE FOR BALLISTIC RESISTANCE EVALUATION: TWO EXPERIMENTAL DATABASES
The field of penetration mechanics covers studies related to materials behavior under impact loading. Usually, the assessment of the ballistic resistance makes use of the V50, the bullet impact velocity with 50 percent probability of perforation of the tested target. However, the estimation of the entire curve of the perforation probability is frequently solicited. Recently, a stochastic model based on the Brownian motion concept has been proposed for that goal. The bullet motion within the target was represented as a stochastic differential equation using the bullet deceleration and a diffusion coefficient. In this paper, the maximum likelihood inference is developed for the estimation of the model parameters. This inference is applied to the complete database (581 observations) and a sample of 20 observations. In both cases, the perforation probability curve is consistent with the confidence intervals on the experimental estimations. The obtained results show that the likelihood inference extends the application of this approach to experimental samples with limited size. In addition, the proposed inference technic is applied to a second experimental database of ballistic impacts to validate the applicability of the proposed modelling methodology using the likelihood inference to various impact cases.
BLAST PRESSURE MITIGATION USING PERFORATED PLATES
The detonation of an explosive system creates high-pressure blast wave in the adjoining media. The interaction of blast wave can inflict severe injuries to humans and catastrophic damage to structures. Many materials such as foams, soil etc., and techniques e.g. reflecting plates, perforated plates, and metallic grids are studied in literature to mitigate the deadly effects of blast waves. In the present experimental study blast wave generator (a short driver section shock tube) is used for the evaluation of blast pressure mitigation in perforated plates of different blockage ratios and hole configurations. These plates with blockage ratio (BR) from 78.79% to 93.43% were deployed inside the driven section of the blast wave generator at a suitable distance from the diaphragm so that blast wave loading occurs on perforated plates. The strength of transmitted blast wave through different plates is measured in terms of peak over pressure using piezoelectric pressure sensors deployed downstream at 0.2m and 0.48 m distances from the perforated plates. The measured strength of the incident blast wave was found to reduce by about 36% to 65% at 0.2 m and about 37% to 73% at 0.48 m downstream through different blockage ratio plates. It was observed from the recorded data that transmitted pressure decreased with an increase in blockage ratio. In the case of the same blockage ratio, the decrease in pressure for a plate with circular holes was more in comparison to a plate having triangular holes and a central hole.
EXPERIMENTAL INVESTIGATION ON PENETRATION OF MASONRY WALL BY LARGE CALIBER RIFLE BULLET
To study the law of penetration action of small high-speed projectiles into the wall, three kinds of large caliber rifle projectiles were used to conduct armor penetration tests on the masonry walls, in which a mortar layer was applied inside and outside of the masonry wall, and the masonry was clay bricks and autoclaved aerated concrete blocks, respectively. High-speed photography of the impact velocity, residual velocity and motion attitude of the projectile, damage pattern, size and penetration process of the target body were obtained. Through the analysis of the kinetic energy loss ratio of the projectile and the wall penetration, it was revealed that the penetration effect of the projectile is mainly determined by the core structure (the single mass projectile is considered as the full core structure), the anti-penetration effect of the masonry wall mainly depends on the strength of the block itself, the anti-penetration effect of the lightweight masonry wall is weak, and the projectile penetrates more easily, the anti-penetration effect of the clay brick wall is the strongest, and also discovered the penetration depends on the thickness of the wall and the location of the projectile impact point. The results of the test and analysis can provide a basis for how to improve the lethality of light weapons against human targets behind the protection of brick walls.
A NOVEL EX-SITU ALUMINUM FOAM-FILLED FOURFOLD-TUBE NESTED SYSTEM AS THE ENERGY ABSORBER
The present research introduces a novel thin-walled structure with an outer tube and three inner tubes as an energy absorber during the lateral compression process. Loaddisplacement response and energy absorption capability of the aluminum foam-filled/empty FT (fourfold-tube) nested tube systems, the TT (triple-tube) nested systems were investigated experimentally. In the quasi-static test, all nested systems were compressed laterally on the universal mechanical tester in compression operation, and the results were subsequently compared. Effects of the aluminum foam on the energy absorption capability and the deformation mode of the foam-filled FT system was analyzed. Experimental results show that the presence of aluminum foam improves the symmetry of deformation of the FT nested system, which is very important in enhancing the energy absorption capability of the FT nested system. In dynamic experiments, impact loading apparatuses SHPB (split Hopkinson pressure bar) and dynamic measurement techniques (high-speed imaging and dynamic strain gauge) were used to test the dynamic deformation mode and the shock resistance of the FT nested system and the TT nested system. Results of the FT nested system were compared with results of the TT system to highlights its advantages of the presented novel FT nested system. The researches demonstrate that the foam-filled FT system can provide a better efficient impact force reduction and desired deformation mode compared to empty FT system. The improved aluminum foam-filled FT nested system can be widely used in engineering fields for enhancing its crashworthiness under impact.
ANALYSIS ON THE CORRELATION BETWEEN BULLETS DEFORMATION AND INCIDENT PARAMETERS OF PISTOL BULLET IMPACT TO CONCRETE
To study the correlation between the bullets deformation characteristics and incident parameters of a 7.62mm lead pistol bullet during impacting to concrete, and to find the sensitivity relationship between each characteristic eigenvalue and quantity parameters, the finite element model of a 7.62mm lead pistol bullet hitting the concrete target was established. The accuracy and effectiveness of the numerical simulation were verified by experiments, and the numerical method can truly reproduce the motion behavior of the bullets in the process of hitting concrete. The results showed that under normal penetration, the angle between the impact surface and the projectile axis can be judged as a normal penetration, the height of the bullet decreases with the increase of incident velocity and is more sensitive to incident velocity, and the deformation of the bullet showed more characteristics under oblique penetration, and the changing trend of each eigenvalue at a different incident angle is similar. In addition, the grey correlation analysis of each eigenvalue of bullets deformation was carried out, and the sensitivity relationship of each eigenvalue to incident parameters was obtained, which provides technical support for the ballistic reconstruction of gun-related cases.
EFFECT ON PREMADE SEPARABLE LESS-PENETRATING PROJECTILE PENETRATING GELATIN TARGET
Less-penetrating projectile has the capability of less penetration and high execution, it attracts international scientific interests for suitability for antiterrorism and anti-hijack. a new projectile which has the structure of pole mushroom shaped cap—premade separable half ring core—indenting jacket were designed for treatment and improving the capability of less penetration and high execution. Both testing and calculation data of 92A pistol projectile and 9mm pistol projectile proved the feasibility of new projectiles design. The result indicates that energy release of “jacket peeled—cap perturbed—core separatedâ€ is more effective than that of traditional projectile. The less penetration, high execution effect and degree of treatment difficulty of premade separable less-penetrating projectile is better than 92A pistol projectile and domestic 9mm low penetration pistol projectile.
STUDY ON ENERGY ABSORPTION CHARACTERISTICS OF ALUMINUM HONEYCOMB/UHMWPE COMPOSITE LAMINATE STRUCTURE AGAINST BALLISTIC IMPACT
In this paper, the effects of pore density and thickness of honeycomb on the compressive deformation and buffer energy absorption characteristics of aluminum honeycomb/UHMWPE (Ultra-high molecular weight polyethylene) composite laminate structure were analyzed by quasi-static compression test and 9mm caliber gun ballistic impact test. According to the test results, the specific energy absorption of the aluminum honeycomb structure reaches 26~34J • cm/g. The maximum deformation depth of gelatin on the back of the aluminum honeycomb/UHMWPE composite laminate structure against ballistic impact decreases by 20% compared with UHMWPE fiber under the same surface density. The increase of the honeycomb thickness can improve the impact resistance of the composite layered structure. The honeycomb pore density and cell wall thickness are proportional to the anti-buffer energy absorption effect and it is inversely proportional to the crack diameter when the bullet impact the honeycomb structure. The aluminum honeycomb/UHMWPE composite laminate structure can absorb the impact kinetic energy of the bullet in a certain extent.
COMPARATIVE EXPERIMENTAL STUDY ON THE CHARACTERISTICS OF PISTOL BULLET PENETRATING GELATIN AND POLYMER SIMULATED MUSCLE TARGET
Polyurethane elastomer material-simulated muscle target-was synthesized by prepolymer with isocyanate hard segment and polyether polyol with long chain soft segment. The polymer simulated muscle target could be stored and used at normal room temperature. Penetration experiments were carried out on gelatin and muscle simulated material target, used 9mm pistol bullet as killing element. Through the comparative analysis of experimental data: when the pistol bullet penetrates the gelatin and polymer simulated muscle target with soft protection, the change process of the depression was basically the same, the difference of the maximum depression depth was 9.64%. In the unprotected penetration experiment, the penetration depth and cavity diameter produced by 9mm pistol bullet penetrating gelatin were consistent with those of polymer simulated muscle target, the difference of the maximum cavity diameter was 12.9%. This new polymer material— muscle simulation marker had better application value in future research.
NUMERICAL SIMULATION OF RHOMBIC FRAGMENT PENETRATING INTO BALLISTIC GELATIN
In order to study the penetration effects of rhombic fragment penetrating into the ballistic gelatin, a numerical model was established by using Ansys/Ls-Dyna. The penetrating process and the transient response of gelatin were simulated using the proposed model which was validated by experiment. The effects of fragment mesh size, model simplification method and incident angle on simulation accuracy were analyzed by numerical simulation. The results indicated that the mesh size significantly influenced the accuracy of numerical results and computing time. The simulation result of the simplified 1/2 model of the fragment was apparently different from the experimental data, while that of whole model was coincident with the experimental results. In addition, the incident angle obviously affected the penetration depth, and the maximum difference of penetration depth at the similar initial velocity and different incident angles was about 40mm.
AN ASSESSMENT METHOD OF BEHIND ARMOR BLUNT TRAUMA BASED ON STUN ENERGY
In order to effectively conduct the evaluation of behind armor blunt trauma (BABT), the stun energy induced by the pressure wave was proposed to evaluate the injury level of BABT. The expression of the stun energy was derived according to the relation between the stress wave propagation in the gelatin and the stun energy. The experiments of several typical bullets impacting gelatin covered with armor were carried out to validate the method of stun energy, and the characteristic parameters of stun energy, the maximum pressure and the pressure impulse were obtained. The assessment results based on stun energy and the score of Maximum Abbreviated Injury Scale (MAIS) in the biological experiments were compared, and it was indicated that the stun energy in the gelatin impacted by different bullets was consistent with the score of MAIS. The evaluation method based on stun energy can be used to quantitatively measure the effects of behind armor blunt trauma.
STUDY ON EFFECT OF BULLETS BLUNTING GELATIN TARGET WITH SOFT ARMOR
Two kinds of 9mm bullets whose armor are all copper, internal steel, lead respectively blunting gelatin target with soft armor are studied in this paper, mechanical responses of gelatin with body armor to non-penetrating ballistic impact is analyzed through the test and simulation research, and the pressure peak of gelatin in specific locations, warhead deformation, the number of layers soft protection through are analyzed, the results of simulation and test are consistent basically, then the accuracy of the simulation model is verified, mechanical parameter such as the pressure, stress in the gelatin, displacement, acceleration are obtained. The results showed that: gelatin is still under big pressure and acceleration shock. The pressure peak of different position can be solved quickly by polynomial fitting of the pressure peak and the impact point distance. The method can be applied in the design and evaluation of different kinds projectiles and soft body protection performance.
STUDY ON THE PENETRATION PROTECTION MECHANISM OF SNIPER PROJECTILE
In recent years, countries have carried out the development of high precision sniper rifle system work, put forward very high requirements for the system precision, so most of the high precision lead was a sniper rifle cartridge adopted structure. By using specific technology and structure, its wounding effect on protected living target is completely different from that of ordinary rifle cartridge. Therefore, this paper will establish a mechanical model suitable for sniper shells to penetrate living targets under individual protection. This paper studies the mechanism of penetration and theoretical mechanical model. On the one hand, the experiment of NIJ II soft protection gelatin target penetrated by lead sniper bullets was carried out. The experimental data of internal pressure of gelatin were obtained by speed test system, highspeed photography, pressure sensor and other experimental equipment, and the fiber destruction form of NIJ II soft protection, deformation and destruction form of lead warhead, and the response of gelatin target under penetration and obtuse attack were analyzed. On the other hand, a theoretical mechanical model was constructed. Energy conservation law was used to decompose the energy in the whole process of projectile penetration target, including deformation energy of projectile, absorption energy of protection and absorption energy of gelatin target. Then the above three energies were refined, and the stress and fiber constitutive model were introduced. By comparing the experimental data and theoretical calculation value, can verify the mechanics model.
STUDY ON BLUNT IMPACT DEFECT OF BIONIC UPPER HUMAN TORSO
In order to explore the injury mechanism of human upper torso under soft protection, ballistic tests were carried out to simulate blunt effect of target on upper torso of bionic dummy under soft protection. Acceleration, pressure, force and other parameters are used to reflect the biological characteristics and injuries of human body under blunt impact effect. The acceleration, pressure, force and other parameters of each part were recorded by impacting the heart, liver, left and right lungs and spleen and stomach at five bullet speeds. Through comparative analysis of different parts of the incident, the parameters of each part of the comparison, study on the impact on the human body. The study of the test results is of great significance to the evaluation and testing of individual soldier protective gear and the study of the damage effect of anti-personnel ammunition on the protected personnel.
ON DEFORMATION OF TWO KINDS OF PISTOL BULLETS DURING PENETRATING INTO C30 CONCRETE
The bullet deformation can truly reflect the speed and angle of bullet penetrating into the concrete, which are often used as an important basis for the reconstruction of trajectory and the judgment of shooting position in the process of case detection. Two types of pistol bullets which are 9mm Barabrum bullet and 51type 7.62mm bullet penetrating into C30 concrete at different speeds were test. The results show that the deformed bullet diameter increases with the increase in impact velocity, and the deformed bullet length decreases with the impact velocity. The relation model of bullet deformation characteristics and penetration velocity is established. The function Y is established to analyze the deformation characteristics of bullet. The relationship between Y value and impact velocity can be regarded as a piecewide linear function. The piecewide speed is consistent with the critical speed of bullet jacket cracking and breaking. The critical speed of bullet jacket cracking and breaking is about 130 m/s for 9 mm bullet and 230 m/s for 51 type 7.62 mm bullet. Function Y can well reflect the deformation law of bullet penetrating into C30 concrete at different speeds.
EXPERIMENTAL STUDY OF TYPE 51 7.62mm BULLET PENETRATION TEST TO THE MINIBUS BODY AND ITS SIMULATED TARGET
The penetrating test of bullet impacting the minibus body was carried out to explore the bullet hole parameters and minibus materials composition. And then the body simulation target was established by analyzing the composition materials of minivan body and the result of penetrating test. The simulated target penetration experiments were carried out with different velocity and angle. The velocity range is from 100m/s to 450m/s, and the angle range is from 15 degrees to 90 degrees. The results show that with the same penetration angle, the width of bullet hole increases with the increase of penetrated velocity. When the angle is 30 degree and the velocity is less than 110m/s, the bullet cannot penetrate the target. When the angle is 15 degree and the velocity is less than 226m/s, the bullet cannot penetrate the target.