9th International Conference on Composite Science and Technology: 2020 - Scientific and Industrial Challenges
Residual Strength Prediction by Numerical Analyses of CFRP Plates Repaired with Flush Scarf Bonded Patch
The widespread use of CFRP laminates in many industrial fields and especially in the aerospace industry, introduces a large number of issues regarding the repair procedures to be adopted due to various kinds of damages. This work aims at providing a numerical FE modelling procedure in order to obtain, for composite laminates repaired by flush scarf bonded patch, accurate results in terms of prediction of the residual strength with the lowest computational cost. The numerical analyses have been developed by using the commercial finite element code ANSYS®. Data from literature, numerical and also experimental, have been used in order to validate the proposed methodology. The stress distribution within the adhesive film and the final residual strength of repaired laminates, loaded in tension, has been used as reference parameters for comparison purpose. Progressive Failure Analysis (PFA) has been performed on composite laminates comparing different mesh modelling approaches and different elastic-plastic material models for the adhesive. As far as the mesh modelling approach is concerned, solid layered and not layered finite elements have been investigated, while in order to simulate the mechanical behaviour of the adhesive, two different material models have been compared: BISO (Bilinear ISOtropic hardening) and ANISO (ANISOtropic plasticity). The results of the numerical analyses performed on the above laminates, provide useful information regarding the advantages and disadvantages of both modelling methods and of both material models of the adhesive, in terms of accuracy and computational costs.
F. DI CAPRIO, R. BORRELLI, U. MERCURIO, F. M. VASSALLO, G. CAPRINO
A Theory of Laminated Beams Subjected to Axial, Bending and Shear Load
A theory of laminated beams subjected to axial, bending and shear loads is presented in this paper. The kinematical model employed to describe the laminated beam displacement field is layer-wise in nature. Moreover it is such that the equilibrium equations and the continuity of the stress components at plies interfaces are satisfied. By using the whole set of interface continuity conditions in conjunction with the traction–free conditions on the beam top and bottom surfaces the layer-wise kinematical quantities are written in terms of the mechanical primary variables pertaining to one layer only, which are then expressed in terms of the laminated generalized displacements. The solution for cantilever beam is last reported to show the soundness of the proposed model.
Numerical Simulations of Low Velocity Impact Damage Onset and Evolution in Carbon Composite Laminates
Laminated composite structures, during their service life, can be exposed to low velocity impact events which can induce internal damage hardly detectable by visual inspections. This internal damage can cause reductions in strength by propagating under loading conditions[1-7]. In this paper, focused on impact induced damage formation and evolution in laminated composite structures, simulations have been performed, which takes into account the on-set and the growth of intra-laminar and inter-laminar damages in composite panels undergoing an impact event and a post-impact compressive load, by adopting a combination of explicit-implicit numerical approaches.
G. DI FELICE, F. CAPUTO, G. LAMANNA, M. ZARRELLI, E. ANTONUCCI, V. LOPRESTO
Composite Structure Panels from Recycled Paper
This paper analyses the development and market potential of composite structure panels and the processing technologies investigated during an industry sponsored project in which the partner company is not equipped to develop new materials beyond immediate application to their own product range. The composite material is based on using recycled paper with a gluing agent. The structural panel will be formed by a single moulding process instead of being fabricated in a number of processes. The shape of the panel has been optimised to reduce its weight and to enable it to be moulded from compounds using a high percentage of waste cellulose aggregates, which are presently either discarded from reclamation processes, or recycled into disposable products. Test samples produced at Nottingham Trent University (NTU) Civil Engineering laboratory have been tested to evaluate the influence of varying gluing agent ratio, moulding temperature and processing time in the mould on the composite material’s mechanical properties. For the structured panel an appropriate ribbing scheme is developed to minimise its weight.
CFR PEEK Composites for Orthopaedic Applications: Assessment of the Macro- Mechanical Properties for Implant Design
In order to investigate novel approaches to the design of polymer matrix compositebased orthopaedic implants, a macro-mechanical characterization of two different injection moulded CFR PEEK materials has been performed. Results have been compared to a theoretical prediction of the composite mechanical properties, after having assessed the resulting composite typology of the realized specimens. The preparation of a stiffness tensor matrix for a failure criteria implant design approach was possible.
S. FUSI, R. FAVALORO, P. DALLA PRIA, P. BRACCO
Innovative Anti-Crash Absorber for a Crashworthy Landing Gear
This paper defines an innovative concept to anti-crash absorber in composite material to be integrated on the landing gear as an energy-absorbing device in crash conditions to absorb the impact energy. A composite cylinder tube in carbon fiber material is installed coaxially to the shock absorber cylinder and, in an emergency landing gear condition, collapses in order to enhance the energy absorption performance of the landing system. This mechanism has been developed as an alternative solution to a high-pressure chamber installed on the Agusta A129 CBT helicopter, which can be considered dangerous when the helicopter operates in hard and/or crash landing. The characteristics of the anti-crash device are presented and the structural layout of a crashworthy landing gear adopting the developed additional energy absorbing stage is outlined. Experimental and numerical results relevant to the material characterization and the force peaks evaluation of the system development are reported. The anti-crash prototype was designed, analysed, optimized, made and finally the potential performances of a landing gear with the additional anti-crash absorber system are tested by drop test and then correlated with a similar test without the anticrash system, showing that appreciable energy absorbing capabilities and efficiencies can be obtained in crash conditions.
Compartmented Fibres for Multiple-Healing of the Polymeric Matrix in Fibre Reinforced Composites
Healing functionality of composites made of thermoplastic matrix with embedded compartmented fibres was evaluated. It was found that the compartmented fibres lead to partial recovery of the initial mechanical properties of the composite. Micro-computed tomography combined with off-axis flexural test showed the ability of compartmented fibres to perform multiple healing in polymer matrices
Buckling and Geometrically Nonlinear Analysis of Sandwich Structures
In this work a finite element model is presented for buckling and nonlinear analysis of multilayer sandwich plates and shells, with a soft core sandwiched between stiff elastic layers. The finite element is obtained by assembling all element-layers through the thickness using specific assumptions on the displacement continuity at the interfaces between layers, but allowing for different behaviour of the layers. The stiff elastic layers are modelled using the classic plate theory and the core is modelled using the Reddy’s third order shear deformation theory. The present finite element model is a non-conforming triangular plate/shell element with 24 degrees of freedom for the generalized displacements. This model is applied in the solution of illustrative examples and the results are presented and discussed.
A. L. ARAÚJO1, V. M. FRANCO CORREIA1, C. M. MOTA SOARES, C. A. MOTA SOARES
Comparison of New Design Guidelines for Composite Cylindrical Shells Prone to Buckling
Currently, imperfection sensitive shell structures prone to buckling are designed according to the NASA SP-8007 guideline, from 1968, using its conservative lower-bound curve. In this guideline the structural behavior of composite materials is not appropriately considered, since the imperfection sensitivity and the buckling load of shells made of such materials depend on the lay-up design. Due to the fact that this approach is outdated for preliminary design purposes, several authors are investigating less conservative methodologies. Some authors propose a new lowerbound curve approach based only on statistical analysis of experimental test on composite cylinders. The problem with this approach is that the range of applicability is limited to the database extension. Finite element models are also used by many researchers to characterize the behavior of cylindrical shell considering different types of material and geometrical imperfections. A representative finite element model allows studying a widespread area of possibilities from the design point of view. In this context a numerical investigation about the different methodologies to characterize the behavior of imperfection sensitive composite structures subjected to compressive loads up to buckling is presented in this paper. A comparative study is addressed between new deterministic methodologies, such as the “Single Perturbation Load Approachâ€ proposed by the European project DESICOS and new statistical approaches based on experimental test on composite cylinders. The aim of this work is to define the range of applicability of these methodologies for unstiffened composite cylinders, advantage and disadvantage to use as a design tool, to provide means to calculate less conservative knock-down factors than the obtained with the NASA SP-8007 guideline.
R. ZIMMERMANN, S. G. P. CASTRO, R. DEGENHARDT
Finite Element Simulation of Different Failure Modes for Buckling-Restrained Braces under Cyclic Loading
Conventional concentric braces buckle under compressive loading. To overcome this limitation, the Buckling-Restrained Braces (BRBs) were introduced in the mid 70’s. They typically consist of a low-yield steel core and a restraining mechanism. In order to achieve enhanced understanding of the BRB inelastic behavior and failure mechanisms, comprehensive experimental efforts are typically needed. When such experimental programs are unfeasible or impractical, other investigative means are valuable. The presented paper explores the most common BRB failure modes observed through detailed nonlinear Finite Element Analysis (FEA). The FEA is carried out using the commercial software ABAQUS taking into consideration both material and geometric nonlinearities. The FE model is maliciously verified against experimental tests reported in the literature and good correlation is observed. The verified FE model is further utilized to simulate different failure scenarios for BRBs under reversed loading. It is found that among the different failure modes, necking of the steel core is potentially the most serious. It could trigger significant internal damage to the BRB upon subsequent compressive load reversal leading to failure of the entire brace via global buckling.
Deterministic vs Probabilistic Burst Prediction of Wound Composite Pressure Vessel
This paper shows the analysis of a wound composite pressure vessel submitted to high pressure hydrogen. A CDM model has been developed which describes phenomena such as different types of damage, residual strains and viscosity. Two different versions of this model have been tested, a deterministic one and a probabilistic one where fiber ruptures are modeled following a stochastic rupture law
Composite Structural Analysis of Wind Blade for Multi-Mw Class Wind Turbine
This paper provides an overview of the failure mode estimation with 3D structural finite element (FE) analysis of wind turbine blade. In order to predict the realistic behavior in the whole blade region, bucking stability, fiber failure (FF) and inter-fiber failure (IFF) analysis were applied to account delamination or matrix failure on composite materials. The Puck’s fracture criteria were used for the IFF evaluation. The design loads for the blades which are applicable to the multi-MW wind turbine system were calculated according to GL guideline and the IEC 61400-1 standard, assuming class IIA wind conditions. After the post-processing of ultimate load results, a number of principal load cases were selected and they were converted to the applied forces at the each section along the blade’s radius of FE model. A nonlinear static analysis was performed for the laminate failure, FF and IFF analysis, and a linear eigenvalue analysis for buckling stability analysis. As a result, the failure mode and the major weak point location could be estimated.
Delamination Growth in Damage Tolerance Composite Structures
The susceptibility of composites to damage has proved to be a critical factor in structural design. Despite their apparent superiority to metals they develop inherent problems; the difficulty to detect internal damages that require expensive NDI (non destructive inspections), such as ultrasonic scans, to detect for instance interlaminar delaminations. This is one of the most common failure modes for composite structures, especially for compression loads reducing drastically the structural capability. Thus, many investigations are analysing composite delaminations onset and growth, and there is a growing interest in developing FEM tools able to perform accurate simulations. In general it has been found that the simulation tools are complicated and computationally expensive, and there is in many cases a considerable difference in the structure behaviour between the simulation and the tests. Many tools are based on the Virtual Crack Closure Technique (VCCT), which is widely applied for computing the energy release rates based in FEM analyses results. This technique allows both prediction of delamination onset and growth under static loads, however the technique is dependent of the FEM methodology used (mesh size for instance) and the parameters of the non – linear analysis. When referring to commercial FEM codes, there are many limitations on the control of the delamination growth algorithm, on the robustness and convergence and on the processing time. This paper explains in detail an “in-houseâ€ tool developed at INTA, that based on the Modified VCCT theory and using non-linear static solution (MSC.Nastran SOL 106) as base code, simulates the delamination growth of a composite structure with initial delaminations. The FEM methodology required for this purpose is also explained in detail, and a comparison between simulation and test results is given, showing an accurate correlation. The investigation also covers different mixed module failure criteria (linear, power law, K
R. GONZÃLEZ, J. SAN MILLÃN, J. GARCÃA-MARTÃNEZ
Experimental Study of Corner Shaped Composite Laminates Subjected to Pure Bending
Composite corners are generally tested under four point-bending to identify Interlaminar Strength Design values. Hereafter different lay-ups have been defined in order to characterize very different damage evolution processes. This evolution monitoring has been performed with the help of Digital Image Correlation, Acoustic Emission and Fast Video Recorder. The different processes leading to the final failure have been precisely identified. A qualitative evaluation of the effect of surface roughness of free edges on the failure load is presented.
L. MICHEL, C. ESPINOSA, F. LACHAUD, R. PIQUET
Evaluation of Delamination Propagation in a Composite Structure Under Vibration Loading
In this paper the ability of delamination to propagate under vibration loading is investigated through adapted numerical approaches. On the one hand a linear approach is adopted for propagation delamination under pure shear modes: II and III. On the other hand a non-linear approach to crack opening under mixed mode I/ II propagation is set up to deal with intermittent contacts of delaminated parts during vibration. The effects of different positions and sizes of the delamination on dynamic behavior are considered in the study cases of a beam and a plate. Evaluation of propagation is achieved by Strain Energy Release Rates computation.
L. MICHEL, M. FRESSINET, F. LACHAUD, Y. GOURINAT
A Numerical Study on Inter-Laminar Failure Mechanisms Evolution in a Composite Wing Box Under Bending Loading Conditions
In this paper, a numerical study has been carried out on skin delamination and skin-stringer debonding growth interactions in a composite wing-box under bending loading conditions. The adopted numerical model uses the Virtual Crack Closure Technique to simulate the inter-laminar damage evolution and the numerical analyses have been performed by means of the FEM code ABAQUS. Three wing-box configurations have been investigated. The first configuration is characterized by only one skin delamination while the other two configurations foresee the concurrent presence of one skin delamination and differently sized skin stringer debondings. The numerical results obtained for all the investigated wing-box configurations have been assessed and compared each other in terms of delaminated area evolution, delamination growth initiation load and strain distributions in order to investigate the influence of the simultaneous presence of the two damages on delamination growth evolution and on the global behavior of the wing-box.
A Nonlocal Continuum Approach for Progressive Damage in FRP Materials
In this paper, a progressive damage model for fiber-reinforced composite materials based on work of Yen and Caiazzo [1] is coupled to a nonlocal regularization technique proposed by César de SÃ¡ et al. [2] in order to prevent strain localization and strong mesh sensitivity of the solution in presence of material softening. The proposed material model is implemented in commercial explicit finite element code ABAQUS via the Vectorized User MATerial subroutine VUMAT and its effectiveness is assessed through the simulation of progressive damage growth around a notch in a composite laminate under loading condition. It is shown that the implemented numerical strategy is able to decrease the pathological mesh dependency and strain localization phenomenon inherently present in a damage local model.
On the Evaluation of Delamination Resistance in Composites
This paper critically discusses the state-of-the-art in evaluating delamination resistance in composite materials and structures. It identifies the appropriate parameters for similitude in quasi-static and fatigue delamination growth predictions, and highlights the significance of presenting the fatigue delamination resistance against both the monotonic and cyclic components of these parameters. Based upon the results being presented it emphasizes the way forward in delamination resistance evaluation.
Fatigue Damage Evolution in Notched Composite Plates
Composite materials, increasingly adopted for structural applications, due to their specific stiffness and strength characteristics, are, characterized by complex failure mechanisms interacting each other. These failure mechanisms, under certain loading conditions, can influence the load carrying capability leading to a premature failure of the structure. In order to address this issue, in this paper, a damage propagation numerical model based on customized failure criteria and gradual material degradation rule is proposed. The numerical model has been implemented, by means of FORTRAN user subroutines (UserMat), within the FEM code ANSYS©. The resulting numerical tool is able to simulate the progressive failure in layered structures under arbitrary multi-axial static and fatigue loading conditions. A preliminary validation against literature experimental data on notched composite plates under static and fatigue loading conditions is presented. Comparisons with experimental results have confirmed the effectiveness of the numerical tool in predicting the composite behaviour taking into account static failure mechanisms and fatigue material degradation at ply level.
Modeling of Fatigue Damage Evolution in Composite Multilayered Cylindrical Shells
This work presents modeling and numerical analysis of shells with axisymmetric or embedded elliptic delaminations. Numerical studies are conducted including cyclic buckling, contact problems in the post-buckling range and optimization problems associated with searching for the minimum of the crack growth per one cycle. Finally, the fatigue life is estimated with the use of the fuzzy set approach.
Numerical and Experimental Investigations on the Micro Damage Accumulation and Its Effects on the Longitudinal Compressive Strength of Carbon Fibre Reinforced Plastics (CFRP) Under Fatigue Loading
The prediction of the fatigue life of components made of fibre reinforced plastics (FRP) under arbitrary cyclical load is a challenge, which is still not met. For a reliable design of such components, an elaborate understanding of the damage process in the material and its effects on the load carrying capacity of the structure is inevitable. Depending on their loading conditions, laminates made of FRP fail by one of the macroscopic failure modes named fibre fracture, inter-fibre fracture or delamination. It is commonly assumed that prior to these macroscopic failure phenomena micro cracks occur and accumulate under cyclic load. Micro damage here denotes as matrix cracks as well as fibre/matrix debonding with crack lengths in the order of magnitude of the fibre diameter. Micro damage results in the degradation of transverse stiffness and strength properties but also affects the longitudinal strength properties of FRP. In this paper, the micro damage process due to fibre transverse preloading and its effects on the fibre longitudinal compressive strength of carbon fibre reinforced plastic will be discussed. For the investigations a combined approach of experimental investigations , d e p o l e v e d n e e b s a h l e d o m l a c i r e m u n A . d e u s r u p n e e b s a h s n o i t a l u m i s l a c i r e m u n d n aw hich allows for the investigation of the effect of fibre/matrix debonding on the longitudinal compressive strength. A 3D unit-cell model has been set up to investigate the effect of location and extent of fibre/matrix debonding on the longitudinal compressive strength. In the experimental part, a specimen concept has been developed. The specimens consist of one testing layer, on which the desired effects have been investigated and a supporting layer to create the desired stress path. The testing layers have been preloaded at different loading paths in the σ2/τ21 stress plane for a predefined amount of cycles at constant stress amplitudes and mean stresses. After this preloading, the fibre longitudinal compressive strength has been evaluated and is compared to the strength without preloading. The comparison between the numerical and experimental investigations show that the damage process of transversely loaded layers of FRP is highly dependent on the loading path and that the micro damage process strongly depends upon the characteristics of the matrix material.
Numerical Modeling of the Interlaminar Fracture of Glass Fiber Epoxy Composites
The objective of present work was the development of numerical models able to predict delamination in glass/epoxy laminated composites under mode I and mixed loading mode. The numerical model, developed with Marc-Mentat 2011 software, was composed of linear isoparametric elements and interface elements placed ahead of initial crack tip. Experimental work was developed to obtain the critical release energy (Gc) and the elastic properties of the laminates. The total fracture toughness increases with the mode II loading component and that linear mixed-mode fracture criteria reproduces the GI versus GII relationship. Force versus displacement experimental curves were obtained and compared with the numerical model prediction. A good agreement between both curves was obtained.
J. A. M. FERREIRA, F. V. ANTUNES, C. CAPELA3
Fatigue Testing of CFRP Aeronautical Laminates for Bearing Behaviour Characterisation
Fatigue behaviour of fastened joints represents a critical issue for aeronautical structure, considering also that a notable amount of data has been collected for static behaviour. In this work, fatigue test of riveted single lap joint made of carbon/epoxy laminates were carried out at different load levels and test frequency. Experimental results showed the importance of monitoring the temperature field in the region between fasteners. Moreover, the evaluation of the residual strength of specimen previously subjected to fatigue load showed a notable improvement of all the mechanical properties.
DBEM Simulation of a FML Full Scale Aeronautic Panel Undergoing Biaxial Fatigue Load
This paper concerns the numerical characterization of the fatigue strength of a flat stiffened panel, designed as a fibre metal laminates (FML) and made of Aluminium alloy and Fibre Glass FRP. The panel is full scale and was tested under fatigue biaxial loads, applied by means of a multi-axial fatigue machine: an initial through the thickness notch was created in the panel and the aforementioned biaxial fatigue load applied, causing the crack initiation and propagation. The fatigue test is simulated by the Dual Boundary Element Method (DBEM) in a two-dimensional approach, followed by a 3D BEM sub-modelling analysis, needed to justify the assumptions made in the bidimensional approach and concerning the delamination area and the fibre integrity during the propagation. Due to the lack of experimental data on the size of the delamination area (increasing as the crack propagates), the latter is assessed by the aforementioned iterative 3D BEM analyses, considering the inter-laminar stresses and a delamination criteria. This approach aims at providing a general purpose evaluation tool for a better understanding of the fatigue resistance of FML panels, providing a deeper insight into the role of fibre stiffness and of delamination extension on the stress intensity factors. The experimental test was realized in the context of a European research project (DIALFAST).
Mechanical Properties and Microstructures of Exfoliated Graphite Nano Platelet Reinforced Thermoplastic Nanocomposites
Exfoliated graphite nano platelets (EG) were fabricated and processed with high density polyethylene (HDPE) to produce EG/HDPE composites. Different compositions of EG/HDPE were prepared: 0%, 1%, 2.5%, and 5% weight of EG. The mechanical properties and microstructures of the composites were investigated. EG was fabricated using natural flake graphite (NFG) with 300μm diameter size. NFG was then intercalated using a Perchloric Acid and Potassium Permanganate (KMnO4) system. The intercalated graphite was expanded at 800oC, and then was sonicated for 6 hours. The produced exfoliated graphite possessed a mean diameter of 38.5μm and a thickness of around 15nm. It was called EG1. Asreceived and ball-milled EG with mean diameters of 9μm and 2μm and thicknesses of 8nm and 4nm, respectively, were also used, designated as EG2 and EG3. EG and HDPE were pre-mixed by a mechanical disperser in the presence of an isopropyl alcohol (IPA) solvent and then dried. EG/HDPE composites were then fabricated using a twin-screw extruder, followed by injection molding. Hardness, tensile and impact tests were carried out to evaluate the performance of these composites. 5% EG1 increased the tensile modulus of elasticity of the EG/HDPE composite by 24% and the yield stress by 5.5%. The ultimate tensile strength, on the other hand, experienced a reduction of 4.7%. A bigger particle sized EG1 resulted in a higher increase of the tensile modulus in a 1% EG loading compound, compared to EG2 and EG3. EG3 with the smallest particle size showed lower tensile properties, due to an EG agglomeration in the HDPE Matrix. The hardness exhibited no changes in all composition, whereas impact strength decreased in general.
Fatigue of Glass Fiber Reinforced Polymer (GFRP) Strips Incorporating Carbon Nanotubes
Fiber reinforced polymers (FRP) have been widely used as a retrofitting material for concrete and steel structures. Recently, carbon and glass FRP rebars have been replacing conventional steel reinforcement in many applications because of their high strength and corrosion resistance. A major challenge that limits the use of Glass fiber reinforced polymers (GFRP) is its poor fatigue performance. Structural design codes suggest limiting the fatigue design strength of GFRP to about 20% of its tensile strength thus making it a non-economical alternative. In this paper, fatigue behavior of GFRP with and without carbon nanotubes (CNTs) was experimentally investigated. GFRP coupons with 0% (neat), 0.5% and 1.0% CNTs were tested under cyclic fatigue loading to extract their fatigue strength. The fatigue maximum and minimum stresses were chosen as 50% and 5% of the ultimate tensile strength respectively. While conventional GFRP coupons ruptured at an average of 87,000 cycles, GFRP coupons with 0.5% and 1.0% CNTs passed a half million cycles without rupture showing increase in fatigue life of GFRP in excess of 475%. The addition of low proportions (0.5%) of CNTs proved to significantly improve the GFRP fatigue strength. Microstructural investigations showed CNTs to be well dispersed in the epoxy matrix. This increased epoxy shear strength and limited damage evolution which improved the fatigue strength of GFRP.
Interlaminar Fracture Toughness of Woven Carbon Fabric Composites Reinforced with MWCNTs
Double cantilever beam (DCB) tests have been carried out on woven carbon fabric composite specimens produced using carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNTs)/epoxy nanocomposites to determine their mode I interlaminar fracture toughness of the specimens. In addition to the neat epoxy woven fabric composite specimens, three loadings of COOH-MWCNTs were examined in this study: 0.5%, 1.0%, and 1.5%. The loading and the resistance curves (R-curves) for all specimens were compared. The results showed a 52%, 91% and 160% increase in maximum critical energy release rates with the addition of 0.5%, 1.0% and 1.5% MWCNTs respectively. It is suggested that additional energy consumption mechanism due to the bridging effect of the COOH-MWCNTs at the interface increased the interlaminar fracture toughness. Furthermore, the significant deformations observed at the interface suggests that linear elastic fracture mechanics (LEFM) method of analysis should be replaced by elastic plastic fracture mechanics (EPFM) or quasi brittle fracture mechanics (QBFM) to accurately determine the fracture toughness of FRP composites reinforced by carbon nanotubes (CNTs).
CNT Coating for Multiscale Carbon Fibre Composites
In recent years Carbon nanotubes (CNTs) have been found to be have extraordinary effects on the properties of composite structures. Generally the most desired properties for composites are toughness and hardness and recently a number of studies have focused on the enhancement of interfacial bonding between composite fibres and polymer matrix material in order to increase the mechanical properties of the final laminate This paper reports on two different techniques for the coating of traditional carbon fabrics with nanotubes to enhance the interaction between constituent fibre yarns. In the first technique CNTs were dispersed in a range of solvents via ultrasonic mixing and then either sputtered onto the fibres using a modified spray-gun or alternatively applied to the fibres using a pipette. A second batch of solutions was prepared dispersing CNTs in the same solvents with the addition of Gum Arabic to the formulation. The use of Gum Arabic leads to the creation of a continuous film, which allows nanotubes to completely cover the fabric surfaces and to bridge larger gaps between the fibre yarns. In addition, Gum Arabic is able to exfoliate and stabilizes the nanotubes in solution increasing their shelf-life.
Flexural Properties of Epoxy and Epoxy-Based CFRP Filled with Carbon Nanotubes
The aim of this work was to determine the effect of carbon nanotubes (CNTs) on elastic and viscoelastic properties of epoxy resin used in CFRP in the matrixdominated flexural testing mode. Two different compositions of RTM6 epoxy resin and CNTs (0 and 1% wt.) were prepared by ultrasonication method. Neat and CNTs containing CFRP specimens [0/45/90/-45]2 were prepared by resin transfer moulding. Three point bending tests were carried out for nanocomposite (NC) and CFRP specimens at room temperature in quasistatic and cyclic creep regimes. Four cycles of gradually increasing stress equal to app. 25, 50, 75, and 90% of flexural strength were used for loading during 30 min followed by 30 min of unloading. The main effect of CNTs was observed for the reduction of creep compliance of epoxy (40%) and CFRP (30%), especially at higher stress levels. Furthermore the results obtained for NC showed an increase in flexural modulus by 11%, reduction of strain at break and flexural strength by 28 and 20%, accordingly, in relation to CNTs content. CFRP with 1% of CNTs showed slight improvement in flexural modulus (by 9%) and strength (16%) in comparison with the neat CFRP.
,A. ANISKEVICH, M. ZARRELLI, A. MARTONE, M. GIORDANO
Melt Spun PET/CNT Nanocomposite Fibers: Effect of CNT and Post Drawing Process on the Mechanical Properties
Carbon nanotubes (CNT) have found profound interest in advanced material composites due to its exceptional properties. With the modulus of elasticity in the range of 1.2 TPa and the strength of 60 GPa, it plays a vital role in strengthening the relatively softer plastics and acts as a good reinforcing element. However, the reinforcing CNT needs to be well distributed in the polymer matrix and to a greater extent is to be well aligned along the longitudinal direction. The issue of CNT distribution can be addressed by using an extruder with good mixing capability, such as a twin screw extruder. The alignment of the CNT in the matrix can be achieved by adopting a suitable processing method, such as a fiber melt spinning process. The high draw ratio of melt spinning process is well known for producing highly oriented polymer molecules and in analogy, it is expected to highly orient the nanotubes. However, considering the fact that the CNT has very low density, it is possible that the CNTs are partially aligned during the melt spinning process. Thus, there is a need to further post process the composite in order to utilize the reinforcing element properties to its maximum extent. In the current study, a co-rotating twin screw extruder with 3 zones of mixing elements was used to produce nanocomposite fibers (PET/CNT) of polyethylene terephthalate (PET) and carbon nanotubes (CNT). The polymer and CNT are fed by two separate feeders. The polymer is fed at the entrance, whereas the CNT is fed at three different positions on the extruder barrel where the mixing zones are located. A constant CNT concentration of 1wt% was considered for the present study. The melt spun fibers were later post drawn in solid state at a speed of 50 mm/min at room temperature. The addition of 1 wt% CNT enhanced the mechanical properties of PET/CNT nanocomposite fibers and this has been discussed in our previous studies. Further, the post drawing of these fibers is expected to have a better alignment of CNT within the matrix. This leads to an increase of 340% in modulus value of the 1wt% PET/CNT nanocomposite fibers. The tensile strength was enhanced by 390% and the yield strength by 85% in comparison to the nanocomposite fibers before drawing. This huge increase in mechanical properties of PET/CNT nanocomposite fibers is attributed to the presence of CNT, its distribution and alignment in the PET matrix as shown in the scanning electron microscope (SEM) images.
M. R. FAROOQUI, Z. ALAM, M. ATIEH, K. MEZGHANI
Melt Spun LLDPE/CNT Nanocomposite Fibers: Effect of CNT and Ultraviolet (UV) Degradation on Mechanical Properties
Polymers are susceptible to degradation when exposed to radiations. These radiations reduce the life span of the polymer products. Many natural and synthetic polymers are attacked by ultraviolet (UV) radiations and products made using these materials may crack or disintegrate, and is a common problem in products exposed to sunlight. Continuous exposure is a more serious problem than intermittent exposure, since attack is dependent on the extent and degree of exposure. Carbon nanotube (CNT) is a good candidate to counter the degradation of polymers. In this study, special fibers of linear low-density polyethylene (LLDPE/CNT) nanocomposite, with good strength, are melt spun using a twin screw extruder with multi mixing elements and a 10 hole-spinneret. These nanocomposite fibers are processed from the melt at 275°C and a mass flow rate of 1.9 g/min. Specially made aligned-carbon nanotubes are used with an average diameter of 30 nm and an average length of 500 μm. These CNTs are mixed with LLDPE melt in three consecutive mixing stages inside the twin screw extruder. This three stage mixing process produces nanocomposite fibers with well dispersed CNT in the LLDPE matrix. Nanocomposite fibers of pure LLDPE reinforced with 1 wt% of carbon nanotubes were artificially exposed to UV rays for 1000, 3000 and 10,000 minutes. Effect of UV exposure was analyzed by mechanical testing and DSC analysis. The mechanical properties such as yield stress, tensile strength and modulus of LLDPE/CNT were relatively stable for up to 3000 minutes of UV exposure compared to pure LLDPE fibers. There was a significant degradation in mechanical properties of pure LLDPE with increase in UV exposure time. With the addition of CNT to LLDPE, the UV degradation was prevented up to 3000 minutes exposure. Initially, with the addition of CNT the mechanical properties of the nanocomposite fibers decrease, however, upon exposure to UV rays for 10,000 minutes, the yield stress, tensile strength and modulus of 1 wt% LLDPE/CNT were found to be 20%, 79% and 33% higher compared to pure LLDPE fibers, respectively. The CNT based LLDPE nanocomposite has less degradation compared to the pure LLDPE.
S. ALAM1, M. R. FAROOQUI, F. M. PATEL, M. ATIEH, K. MEZGHANI
Mono and Polyamine Functionalized MWCNTs as Reinforcement for Epoxy Resin Based Nanocomposites
Carbon nanotubes represent nowadays an ideal reinforcing filler due to their very high aspect ratio, an extraordinary mechanical and electrical property. They, employed as reinforcement in epoxy nanocomposites, can widen their application in potential application such as coatings, adhesives, structural materials etc., ranging its application from microelectronics to aerospace. Anyway, the enhancements of the properties due to the insertion of CNTs can be less than the theoretically expected benefits due to the various difficulties of processing, determined by both dispersion degree of filler throughout the composite system and their interfacial adhesion. In order to overcome these difficulties in this paper we studied the effects of functional groups (both mono and poly amine chain) attached on external wall of multiwall carbon nanotubes on the MWCNTs/epoxy nanocomposites. The aim was to verify the role of the functional groups on the properties of the nanocomposites. In order to highlight the features of MWCNTs/epoxy system, mechanical flexural, morphological, calorimetric and electrical measurements were carried out. The effects of the amino functional groups were compared to the neat resin. The results have shown that the most important changes in the properties of the material can be related to an improvement of the dispersion of the filler in the matrix. Furthermore, the increase of the number of amine groups on each single chain lead to an increase of toughness, strength and deformability of the nanocomposites. This behavior was related to an interfacial interaction filler/matrix; an interaction model was proposed and discussed.
V. BRANCATO, A. PISTONE, D. IANNAZZO, A. PIPERNO
Comparative Assessment of the Graphene Oxide and Reduced Graphene Oxide Influence on the Zeta Potential of Selected Bacteria in Drinking Water Environment
Microbial adsorption to solid surfaces plays a fundamental role in bioengineering, food processing, environmental protection, medicine and medical biotechnology as well as power industry and water filtration [1]. It is generally accepted that nanomaterials are providing great opportunity to develop bioactive sorbent materials which can be used as electrodes in fuel cells as well as separation media in water purification to remove inorganic and organic pollutants from contaminated water. They offer a number of advantageous physicochemical properties. On a mass basis, they can be characterized by much larger surface area and surface bioactivity than their bulk counterparts [2]. Nanomaterials can also be functionalized with various chemical groups which allow selectively targeting key biochemical constituents of waterborne bacteria and viruses [3]. Several research groups were exploring the sorption properties of nanomaterials such as: multiwalled carbon nanotubes [4,5], or chemically activated carbon fibers [6]. So far, graphene and graphene oxide also attracted great scientific attention as a potential effective sorbents. The knowledge of the electrochemical properties of microorganisms is also of benefit in explaining bacteria adsorption processes and resulting formation of biofilms. Bacterial cell electric properties can also be characterized by the zeta potential. The primary objective of this study was to describe the graphene oxide and reduced graphene oxide influence on the zeta potential of selected bacteria with a special emphasis on the analysis of the zeta potential distributions as a function of pH. Due to acquire comparable investigations results of the influence of graphene oxide and reduced graphene oxide on the zeta potential of bacteria, it is vital to perform experiments on an appropriate material. Thus, in our study, for graphene oxide reduction we have chosen thermal annealing (under vacuum) method due to acquire reduced graphene oxide, characterised by similar morphology and physical properties to graphene oxide but differing in surface chemical composition.
A. M. JASTRZĘBSKA, E. KARWOWSKA, A. OLSZYNA
Static and Fatigue Strength Characterization of Sisal Fiber Reinforced Polyester Composite Material
Sisal fibers are one typical type of natural fibers that are currently being looked at as alternatives to inorganic fibers to be used as reinforcements on polymer matrix composites (PMCs). Natural fiber reinforced plastic (NFRP) composite materials are generally sought after by manufacturers because of their sustainability, biodegradability, low cost and mechanical characteristics. In this work, sisal fibers that were extracted from the Agave Sisalana plant are used to reinforce a polyesterbased resin using a molding technique at low pressure resulting in a cross ply biocomposite laminate with around 25% Fiber Volume Fraction (FVF). Static tests were carried out on specimens that were cut from these laminates and the results showed that the ultimate tensile strength is found to be around 47 MPa. Displacement control and constant amplitude fatigue tests were then carried out at three different levels with a frequency of 5Hz. The fatigue tests results are extensively analyzed using stiffness degradation behavior, S-N curve diagrams, hysteresis loops and energy dissipation versus number of cycles. The fatigue endurance limit (over one million cycles) for these materials is achieved at a stress level of 55% of ultimate displacement. The implication of this work is that the use of these materials in areas such as car and aircraft interiors promises to significantly reduce weight, cost and carbon footprints without sacrificing performance. Keywords: Bio-composite, Sisal/polyester, Fatigue, Stiffness degradation, Hysteresis loops, S-N curves, Energy dissipation
Differential Scanning Calorimetry of Alkali-Treated Water Hyacinth (Eichhornia Crassipes)/HDPE Composites
This research is aimed to study the effect alkali treatment on thermal stability of a new composite made of water hyacinth (Eichhornia crassipes) with HDPE. Water hyacinth fibres were sun-dried and chopped following by immersion in various concentration of alkaline solution, NaOH in 30 min. The concentrations are 5, 10, 15, and 20% in weight. Each alkali-treated fibres were then loaded into an internal mixer together with high density polyethylene to form various alkali-treated water hyacinth/HDPE composites. The composites were then cut into about 10 mg samples and then placed into aluminium crucibles. The sample filled crucible were placed into a differential scanning calorimetry (DSC) instrument and heated from 30 °C to 400 °C. The results show that the thermal stability of the composites increased with the increase of fibre content.
Impact Properties of Water Treated Bamboo/Unsaturated Polyester Composites
This study examined the influence of period of water treatment on the impact toughness bamboo/unsaturated polyester composites. Four types of composites were produced in various period of water treatment during fibre preparation (untreated, 1, 2, 3 hours). The continuous fibres were then mixed with unsaturated polyester by hand lay- up process. Each produced composites were cut to form a rectangular shape with dimensions 80 x 10 x 4 mm. The impact test was then conducted as per ISO 179. It is observed that the highest impact toughness was achieved by 1 h water treated composite. Water treatment in 2 and 3 h resulted in higher impact strength than that of untreated composite but lower than that of 1 h water treated composite.
Thermogravimetric Analysis of Untreated Water Hyacinth (Eichhornia Crassipes)/HDPE Composites
This research is aimed to study the effect of fibre content on thermal stability of a new composite made of water hyacinth (Eichhornia crassipes) with HDPE. Dried stalks of water hyacinth were chopped into short fibres. The chopped fibres were mixed with high density polyethylene (HDPE) using an internal mixer followed by hot-pressing at 140 °C to form untreated composites in various fibre contents (10, 20, 30, and 40% in weight). The samples were then analyzed using a thermogravimetric analysis instrument (TGA) to obtain a thermograph of the composites at the temperature range of 30-600 °C and heating rate of 20 °C/min. The results show that the decomposition temperature of the composites decreased with the increase of fibre content.
Variability in, and Property Prediction for, Natural Fibre Composites
Natural fibres are perceived as a sustainable reinforcement for polymer matrix composites but reported mechanical properties have high variability. The authors have conducted experiments using a single batch of jute fibres and established that the coefficient of variation (CoV) in strain-to-failure is lower than the CoV for modulus or strength [1]. This characteristic appears to arise from the (incorrect) assumption of circular fibre cross-section. Weibull statistics were used to compare the apparent cross-sectional area derived from the diameter measured by optical microscopy transverse to the fibre to the true cross-sectional area measured from sectioned fibres. For the jute fibres studied, the above ratio can be used as a fibre area correction factor (FACF) in the rule of mixtures to generate improved prediction of the composite mechanical properties [2]. This paper will report comparisons between predictions with, and without, the FACF and experimental values for the authors' quasiunidirectional natural fibre composites data. Further analysis considers results from other research groups where sufficient data is available to make the comparison. The modified rules-of-mixture generally result in significantly better predicted values for the modulus and strength of natural fibre reinforced polymer matrix composites.
Potential of Durian Skin Fiber as Reinforcing Agent in PLA Composite
Durio zibethinus Murray, or durian, is seasonal fruit mainly available in tropical Asia. Currently, durian skin is a waste material and there is no specific utilization. Therefore, this study investigated the potential of durian skin waste as reinforcement fiber for biodegradable polymers and green composites. As for preliminary investigation, density, moisture content and dimension of durian skin fiber (DSF) were determined. Density of DSF was about 1.243 g/cm3, moisture content in the ranges of 7.92 to 9.10 % whereas aspect ratio in average of 5.53. DSF was then incorporated into polylactic acid (PLA) for the fabrication of biocomposite. PLA and DSF were compounded using Haake twin screw extruder and then injection moulded. The effect of durian skin fiber content from 0, 10, 20, 30 and 40 wt% on the tensile properties of of DSF-PLA composites was studied. It was found that DSF content at 30 wt% produced the highest tensile strength and tensile modulus. Observation under scanning electron microscope (SEM) revealed the surface morphology of tensile fracture specimen.
M. M. ROMAINOR, M. N. NUR AIMI, W. N. WAN BUSU
Sisal Fibre Bundle Composites—A Review of Properties in Relation to Microstructure
The mechanical properties of natural fibre composites comprised of sisal fibre bundles in thermosetting or thermoplastic polymer matrices are described. Following a brief review of the physical properties and eco-profile of sisal fibres in the context of other plant and synthetic fibers, the statistical variability in fibre bundle strength and interfacial shear strength are examined. Techniques for manufacturing well aligned, low matrix porosity fibre composites are described and the scope for property optimization by fibre surface treatments and densification is explored. The strength of in-line, co-cured joints is reported and an inter-laminated fibre lay-up offers high joint integrity. Fatigue properties and failure modes of sisal-epoxy composites are presented in the form of hysteresis loops and constant life diagrams in reversed loading and tension-tension modes. A method for the manufacture of thermoplastic matrix composites, based on sisal fibers in a poly (lactic acid) (PLA) matrix, is explained and the morphology of crystal growth on the surface of the fibre bundles is described. It is concluded that sisal plant fibre composites have a role to play in engineering with limitations relating to strength, elastic modulus and environmental stability.
Biodegradable Composites Reinforced with Cellulose Nanofiber Extracted from Waste Paper Pulp
We tried to extract cellulose nanofibers from waste newspaper as a high-yield cellulosic source. Waste newspaper was treated chemically and physically in order to extract individualized cellulose nanofibers from the cellulosic pulp materials. The combination of acid hydrolysis and phisical treatments resulted in the cellulose nanofibers of diameter between 10–40 nm. The reinforcing effect of the extracted cellulose nanofibers was investigated by composing with a starch-based biodegradable resin. The results of the tensile tests show significant enhancement in mechanical properties of the extracted cellulose nanofiber- reinforced composites.
A. N. NAKAGAITO, M. S. A. BISTAMAM, J. K. PANDEY
Mechanical Properties of Recycled PP Reinforced with Microcrystalline Cellulose: Effect of MAPP Content
The effect of different amounts of maleic anhydride grafted polypropylene (MAPP) coupling agent (2, 3 and 5 wt%) on mechanical properties of recycled polypropylene/microcrystalline cellulose (rPP/MCC) composites was determined. 4 wt% of MCC was compounded with rPP via melt mixing method followed by injection molding. The mechanical properties of the composites were characterized by tensile and dynamic mechanical analysis (DMA) tests. It was found that at low filler content, different amounts of MAPP resulted in no appreciable change in tensile strength and modulus. Nevertheless, the DMA result exhibited that the composite with 3 wt% of MAPP shows the highest value and temperature in storage modulus and loss tangent, respectively. This result indicates that a strong interaction between MCC and rPP occurred at this specific MAPP amount which also affects the rigidity and thermal property of the composites. It is presumed that the 3 wt% of MAPP will also influence the mechanical and thermal properties of rPP composites at higher content of MCC.
Studies on Mechanical Properties and Thermal Analysis of New Polymer Foam Composites Originated from Coconut Trunk Fiber/Polypropylene/High Density Polyethylene Composites
Use of wood fibers as reinforcement in polymer composites has recently received considerable attention due to environmental concerns associated with petroleum based polymers. This work describes new polymer foam composites originated from coconut trunk fiber (CTF)/ polypropylene (PP)/ high density polyethylene (HDPE) composites. The composites were successfully prepared by conventional foaming method using chemical blowing agent, with different filler content of untreated and treated CTF at 5, 10 and 15 phr were added into PP/HDPE blends. Foams composed of treated CTF/PP/HDPE composites exhibit better properties of cell structure, tensile strength, elongation at break, Young’modulus, compression strength, melting temperature, crystallinity and thermal stability, if compared to untreated CTF/PP/HDPE composites due to better interfacial bonding between filler and polymers. However, it was found that foamability decreases with the amount of CTF added in the PP/HDPE blends increases up to 15 phr due to restriction of cell growth by the wood fibers.
Mechanical Performance of Cement Mortar Composites Reinforced with Cellulose Fibres
The aim of this work is to evaluate the mechanical performance of cement mortar composites reinforced with various percentages of cellulose fibres. Results indicated that for low content of fibres there is a high adhesion between the cement matrix and the fibres and, consequently, the fracture of the composite under flexural stress occurs by rupture of the matrix and the fibres. However, for higher fibre content, the collapse of the material occurs by a progressive rupture of the matrix which is dispersed in a dense network of fibres and which disintegrates, releasing the fibres. These results could be interesting for modelling the mechanical performance of vegetable fibre reinforced cement mortar composites.
Tension Fatigue Behavior of the Laminates Jute/Epoxy
Work presented is interested in the characterization of the quasistatic mechanical properties and in fatigue of a composite laminated in jute/epoxy. The natural fibers offer promising prospects thanks to their interesting specific properties, because of their low density, but also with their bio deterioration. Several scientific studies highlighted the good mechanical resistance of the vegetable fiber composites reinforced, even after several recycling. Because of the environmental standards which become increasingly severe, one attends the emergence of eco-materials at the base of natural fibers such as flax, bamboo, hemp, sisal, jute. The fatigue tests on elementary vegetable fibers show an increase of about 60% of the rigidity of elementary fibers of hemp subjected to cyclic loadings. In this study, the test-tubes manufactured by the method infusion have sequences of stacking of 0/90° and ± 45° for the shearing and tensile tests. The quasistatic tests reveal a variability of the mechanical properties of about 8%. The tensile fatigue tests were carried out for levels of constraints equivalent to half of the ultimate values of the composite. Once the fatigue tests carried out for well defined values of cycles, a series of static tests of traction type highlights the influence of the number of cycles on the quasi static mechanical behavior of the laminate jute/epoxy.
Toughening of Carbon Fibre Composites By Hybridisation with Self-Reinforced Polypropylene
Carbon fibre reinforced polymers often suffer from limited toughness. To drastically increase their toughness, hybridisation with self-reinforced polymers is proposed. The present study focuses on interlayer hybrids of carbon fiber/ polypropylene and self-reinforced polypropylene (SRPP). These hybrid composites are produced in various layups and their tensile behaviour is investigated. It is found that these hybrids possess a unique combination of stiffness, strength and ultimate failure strain. The most interesting observation is the multiple fracture behaviour of carbon fibre plies, which appears at low fibre volume fractions. This has the potential to increase energy absorption in impact loading.
L. GORBATIKH, P. J. HINE, I. M. WARD, I. VERPOEST
Hybridization of Ductile Steel Fibre and SelfReinforced Composites
Hybridization of ductile steel fibres and self-reinforced polypropylene (SRPP) is investigated. The goal is to create a material with a high specific stiffness (stiffness per density) while maintaining a high toughness of constituent materials. Three types of hybrids are produced to assess the effect of the stacking order on the tensile behaviour. The hybrid composites have shown to possess a five times higher stiffness and two times higher specific stiffness compared to the SRPP without any loss in toughness. The classical laminate theory was modified to account for non-linear behaviour of the plies and applied to predict tensile curves of the hybrid laminates.
P. DE CUYPER, Y. SWOLFS, L. GORBATIKH, I. VERPOEST
Behavior of Hybrid Metal Matrix Composites Reinforced with Continuous and Discontinuous Fibers
The appeal of hybrid composites is the ability to create materials with properties which normally do not coexist such as high specific strength, stiffness, and toughness. One possible application for hybrid composites is as backplate materials in layered armor. Layered armor systems employing an energy absorbent backplate can defeat projectiles at lower weights than traditional steel armor, increasing the fuel efficiency and mobility of armored vehicles. Fiber reinforced composites have been used as backplate materials due to their potential to absorb more energy than monolithic materials through microfragmentation of the fiber, matrix, and fiber-matrix interface at similar to lower weights. Composite backplates are traditionally constructed from graphite or glass fiber reinforced epoxy composites. However, continuous alumina fiber reinforced aluminum metal matrix composites (MMC) have superior specific transverse and shear properties compared to epoxy composites. Unlike the epoxy composites, they have the ability to absorb additional energy through plastic deformation of the metal matrix. Although, these enhanced properties may make continuous alumina reinforced MMCs advantageous for use as backplate materials, they still exhibit low strains to failure and therefore have low toughness. One possible solution to improve their energy absorption capabilities while maintaining the high specific stiffness and strength properties of continuous reinforced MMCs is through hybridization. In the past, the strain to failure of multiple low elongation composites has been increased through hybridization with a high elongation component. Two examples include the addition of whiskers to particulate composites and using both high and low elongation fibers in continuously reinforced composites. In an attempt to increase the strain to failure and energy absorption capability of a continuous alumina reinforced Nextel™ MMC, it was laminated with a high elongation discontinuous alumina Saffil® layer. Uniaxial tensile testing of hybrid composites with varying Nextel™ to Saffil® reinforcement ratios resulted in composites with non-catastrophic tensile failures and an increased strain to failure than the single reinforcement Nextel™ MMC. The tensile behavior of two hybrid continuous and discontinuous alumina fiber reinforced MMCs will be reported, as well as a description of the mechanics behind their unique behavior.
Ballistic Impact Analysis on the Advanced Combat Helmet (ACH)—Testing and Simulation
An accurate Advanced Combat Helmet (ACH) finite element model for the effective simulation of projectile-helmet interactions, especially brought on by ballistic impacts, has been developed at the National University of Singapore (NUS). Ballistic tests are performed to impact the combat helmets so as to calibrate the finite element model. A high speed camera is used to capture the dynamic impact sequence of the projectile with the helmet. The paper presents a novel methodology in employing Computed Tomography (CT) to obtain finite element geometry of the combat helmet and in their post-test damage assessments. The CT X-ray technique allows interior intra- and inter-laminar structural damage to be observed and compared with the damage prediction from our micromechanics-based helmet damage model that investigates the extent of matrix compression and tensile damage, as well as fiber buckling and tension failure. There is good correlation between experimental data and simulation results for the deformation and damage characteristics of the Kevlar® ACH up to the ballistic limit of the helmet which included projectile penetration and perforation into the ACH. At 297.6 m/s (the actual projectile speed whereby helmet perforation occurs), simulation shows perforation of two element layers with the flattening of the outermost element layer. With an impact velocity of 315 m/s, simulation shows that the projectile is able to penetrate more than half in-thickness into the laminate. As the helmet laminate began to deform, increasing surface area friction is encountered between the projectile and the contacting laminate. Energy and momentum is taken up to overcome the friction generated between the projectile surface and the perforated laminated layers as the projectile deforms and goes through it. The perforated helmet laminates eventually arrest the projectile’s impending motion as it loses its kinetic energy, and is “stuckedâ€ together with the laminate. For the simulation with projectile impact velocity of 325 m/s, the projectile penetrated through the entire thickness of the Kevlar® helmet with a residual forward velocity of around 50 m/s. Hence, from simulation, the ballistic limit (or helmet perforation velocity) of the ACH, using the steel spherical projectile, is between 297.6 m/s and 325 m/s. This translates to about 9% more speed and 17 % more kinetic energy required by the projectile for helmet perforation than experiment (based on a single test at 297.6 m/s on the helmet specimen). The discrepancy is reasonable considering that the physical helmet has been shot multiple times before the calibration tests and the limited number of ballistic tests conducted due to limited samples.
Impact Behavior of Polypropylene/Glass Fiber Fabric Composites
In this contribution compatibilized and not compatibilized polypropylene/glass fiber fabric composites were prepared and characterized through in terms of both static and low velocity impact response under various impact energies. A good fiber impregnation was achived in all systems, and results emphasized the influence of the fiber/matrix interface on damage modes occurring in laminates after low impact energy and at failure.
D. ACIERNO, L. SORRENTINO, S. IANNACE, P. RUSSO
Effect of Incorporating Foam Based Flexible Blunt Trauma Pads on the Shock Wave Protective Performance of Flexible Body Armour
This paper presents results from shock tube experiments on the transmitted overpressure through multiple layers of ballistic fabrics backed by various foam based flexible blunt trauma pads. The results corroborate previous reports that multiple layers of ballistic protection fabrics alone are not effective in reducing the occurrence of shock/blast wave injury. On the contrary, multiple layers of fabric and flexible laminates (Twaron T717, Twaron UD41 and Spectra Shield SA-1211) amplified the transmitted shock wave pressure. Moreover, this amplification in the transmitted peak pressure increased further when more plies were added. Incorporating foam based flexible blunt trauma pads behind the Twaron fabric resulted in mixed outcomes on the transmitted shock wave depending on the makeup of the blunt trauma pads. Adding pads comprising open cell polyurethane foams resulted in further and significant amplification of the recorded peak pressure. Attempts were made to reduce the pressure amplification by infusing the foams with shear thickening fluid. Although successful in reducing the peak pressure compared to a system of fabric backed by neat foam padding, the transmitted peak pressure was still slightly higher or at best equal to a system of fabrics without any padding. It was also found that padding made of auxetic foams fared better than conventional foams as they did not give rise to the large amplification in peak pressures.
H. P. LEE, T. E. TAY, B. C. KHOO, V. B. C. TAN
Kevlar® Fabrics Modified with SiC Particles
The impact properties of fabrics can be improved by modification of fibers with hard ceramic particles. In this work silicon carbide (SiC) particles dispersion was used for impregnating Kevlar fabrics. Two different modifications were tested: one side and both sides impregnation. Thermo-gravimetric analysis (TGA) was applied to study the modifications in the degradation characteristics of the fabric while single yarn pull-out test was applied to observe the influence of the particles in the frictional properties of the fabric. TGA results showed that SiC addition improved the thermal stability of the fabrics and this effect is more pronounced in the sample impregnated on both sides. Finally, the results of pull-out tests showed that the curves profile was affected by the presence of particles and that the maximum forces necessary to extract a yarn increased by approximately 130% in the one side modified sample and approximately 150% in the both sides modified sample when compared with neat fabric.
Resin Transfer Moulding (RTM) to Produce Surfboard Fins with Natural Fibres
To achieve higher performance in surfboard fins it is necessary to change the materials of construction from thermoplastics to fibre-reinforced composites. The industry generally has high environmental awareness so bio-based materials would be the material of choice if they can be manufactured at sensible cost and perform within the component specification. Resin Transfer Moulding (RTM) is proposed as the technology for the production of composite surfboard fins reinforced with natural fibres.
J. GRAHAM-JONES, J. SUMMERSCALES, W. HALL
Development of Glass-Fiber-Reinforced Polyethylene Roadside Restraints
Replacement of most common semi-rigid roadside barrier system, based on steel w-beam guardrail, by a thermoplastic polymer composite as the guardrail material is considered. With this aim, production technology of E-glass fiber/low density polyethylene composite by a continuous thermoforming process from glass fiber roving, glass-fiber fabric, and polyethylene sheets is being developed. The tensile strength and deformability along the reinforcement direction of the composite material produced has been characterized, and the response upon vehicle impact of the respective restraint simulated numerically and tested experimentally.
V. LEITLANDS, D. ZELENIAKIENÄ–, P. GRIÅ KEVIČIUS, J. ANDERSONS
Microwave Curing of Long Fiber Reinforced Composites for Resin Transfer Moulding
In the present work, microwave radiation has been employed in order to polymerize the resin of long fibre reinforced composites [1]. The research carried out in microwave processing [2] contributes to the following benefits to the composite processing: • Multi-functional polyester, vinyl-ester and epoxy resins suitable for RTM process and microwave curing have been modified. The determination of the dielectric function of the resin and the assessment on microwave susceptors suitable to enhance the curing time is included. They have low viscosity for optimal filling of the mould. After the filling process was completed, a three dimensional microwave system is applied to start the curing of the resin. The curing is an exothermic reaction, so that the microwave only initiated the curing. • This innovative microwave system in connection with a temperature control system ensures a homogenous heating and therefore optimal curing of the resin. The microwave system is developed with the help of simulation software for the microwave field and resulting heating. • The degree of polymerisation of the resin is increased by microwave radiation and the polymerisation degree was close to 100% with a reduction in curing time. Because of the very high degree of polymerisation the styrene emission, particularly during demoulding, can be decreased more than 80%, compared to open mould processes. Process parameters were also studied and compared to the traditional heating process. A cost effective method for composites manufacturing by RTM has been developed. A scaleable microwave system adapted to RTM is being developed for homogenous heating and therefore curing of composite parts. Only the combination of the developed resins and the microwave system with a temperature control ensured a homogenous processing of the part.
M. GRAF, B. MONJE, O. MENES, R. ESCHBACH
Development of an Analysis Tool for the Design of Bonded Composite Repairs
Composite structures are increasingly finding more applications in various fields thanks to their lower weight if compared with other materials of the same strength; this is especially true in the aeronautical field for both military and civil aircraft, as well as for rotorcraft, where composites can be employed as primary and secondary structure in the form of monolithic and sandwich structures. On damage detection, the possibility to scrap the component or repair the damage is evaluated. This decision is determined by several considerations, like the repair costs, position and accessibility of the damaged area. The repair needed to restore the original components stiffness and strength characteristics should be chosen accordingly to specific procedures taking into account the damage typology and the damaged component. Generally, the repair procedures are listed in a Structural Repair Manual (SRM) that should also provide information on the maximum repairable damage for each component. In this paper, a repair design tool implemented in Matlab is proposed. The tool is able to suggest different repair typologies and to choose the proper repair size by performing optimization analyses oriented to best repair solution in terms of adhesive shear stress and length of repair patch.
G. DI FELICE, F. SCARAMUZZINO, A. SELLITTO
Fabrication of Copper/Alumina Composites by Using of Fractional Ceramic
construction for building elements such as insulators for spark plugs in engines, brake pads and components for jet engines and other airplane. In addition, the plastic metal conducts to obtaining materials with improved fracture toughness compared to a ceramic matrix. Both the physical and mechanical properties of this kind of composites are strongly influenced by the properties of its individual components and production techniques. In this paper, prepared copper - alumina composites will be presented. The ceramic preforms were fabricated following the replication method, After processing, the ceramic material obtained replicates the structure of the substrate but with a very low strength. This allowed the destruction of the ceramic preform and to isolate fraction < 200 μm. It is assumed that the addition of the ceramic phase will be 3-10 vol.%. The sintering process ran at 1050 °C for 30 min, at 15 MPa in a hot-press. The main aim of the presented investigations is to study the effect of different additives of ceramic phase on the microstructure and selected mechanical and thermal properties of copper - alumina composites.
K. PIETRZAK1,A. STROJNY-NEDZA, A. WAJLER, A. SIDOROWICZ1, U. BRYKAÅA
Holistic Design Process for Hollow Structures Based on Braided Textiles and RTM
The present paper elaborates a holistic design process to unlock the potential of the mass production-ready manufacturing chain 2D overbraiding in conjunction with Resin Transfer Moulding (RTM). This contains sub-design processes for preform, infusion, mandrel plus mould and manufacturing. They are passed through in the given order. For each sub-process both, individual tasks and reasonable methods to accomplish them are presented. The methods are arranged according to part complexity. The procedure is performed for a medium complex demonstrator part to validate the proposed design process. After manufacturing of prototypes, predicted braiding angles and fibre volume fractions are compared with measured ones. Furthermore, an infusion simulation based on PAM-RTM is checked against mould filling studies.
Processing and Mechanical Characterization of Polymer/Carbon Nanotubes Fiber Reinforced Composites by Innovative Vacuum Infusion Technology
In this study, Multiwalled Carbon Nanotubes (CNT) epoxy glass fiber composites have been manufactured by conventional Vacuum Infusion process and the novel Pulse Infusion technique. Pulse Infusion allows to control the pressure of the vacuum bag on the dry fiber reinforcement and induce a pulsed transverse action to promote the through thickness resin flow by using a proper designed pressure distributor. The realized composite panel have been mechanically characterized by performing flexural tests according with the ASTM D790 standard in order to investigate the effect of the new manufacturing process on the flexural strength and modulus.
M. GIORDANO, M. ZARRELLI, A. LANGELLA, V. ANTONUCCI
Thermal and Mechanical Properties of Epoxy/SiC Composites Degraded by Moisture and Temperature
The amount of degradation that takes place in a polymer composite is related directly to the quantity of moisture it absorbs. Other factors, as temperature and oxygen concentration, can also modify the mechanical properties. Plastification and swelling are among the undesirable consequences of absorbed water. The aim of this work is to investigate the effect of moisture on mechanical properties of epoxy reinforced with silicon carbide. Two different SiC sizes (nano and 10 μm) were studied. In order to quantify the degradation of the composite, the specimens were exposed to three environments (95% RH-relative humidity- and 60 ºC, 95% RH and RT-room temperature, and 5% RH and 60 ºC). Variations of Tg (glass transition temperature), water uptake and mechanical properties were determined as a function of exposure time. Thermal conductivity was evaluated in pristine material and after 31 days in the three environments (30 days in the ageing environment and 24 h of stabilization in a desiccator).
A, M. PANTOJA, M. A. MARTÃNEZ, J. C. DEL REAL
Improvement of Adhesive Behavior of Ballistic Woven Aramid by Atmospheric Pressure Plasma Treatment
The objective of this work is the achievement of improved adhesive properties of woven aramid by means of atmospheric plasma treatments (APPT). The possible resistance decrease of the aramid after modification has been evaluated through tensile test. Surface chemical changes have been studied by contact angle measurements and T-peel tests (with epoxy and polyurethane adhesives) are used to evaluate the improvement in wettability.
Modal Characterization on Recyclable Foam Sandwich Panels
The reduction of the mass of a structure is an important issue in the engineering field since it leads to reduced emissions and operating costs. On the other hand, weight saving often leads to an increase of vibration/noise transmission. For this reason, in the last years the dynamic design of lightweight structures has received more emphasis, particularly in engineering transport applications, where dynamic loads can produce high amplitudes of vibration. At the same time, the research has been also focussed on the use of “green materialsâ€ with the intention to satisfy both weight and sound insulation/vibration suppression requirements using environmentally friendly materials. This paper presents the results of an experimental campaign performed on sandwich panels manufactured by using recyclable foam core and face sheets made from natural and plastic fibres combined with recyclable resin. In order to evaluate the vibrational characteristics, the mode shapes, natural frequencies and damping ratio of the sandwich panels were identified experimentally. The tests were performed by adopting the so-called roving hammer technique. Experimental results were compared with numerical ones, obtained by means of a finite element model. The structural loss factor of these panels was measured using the reverberation time method.
V. D’ALESSANDRO, F. FRANCO, B. MACE, S. DE ROSA
Evaluation of Al-Mg2Si In-Situ Composites, Further Reinforced by TiC Particles after Solution and Aging Heat Treatments
Al7Mg5Si (wt%)-TiC reinforced composites have been produced by flux assisted casting followed by solution and aging heat treatments. The TiC particle addition resulted in a refinement of primary Al grains and Mg2Si Chinese-script morphology, as well as reduction of the Mg2Si phase extent. Both, heat treatment and TiC addition have a positive effect on the microhardness of the Al matrix, as well as the hardness and the sliding wear resistance of Al7Mg5Si. A wear mechanism has been proposed. Electrochemical testing in 3.5% NaCl showed that the TiC reinforcement does not worsen the corrosion performance of Al7Mg5Si. Pitting is mainly associated with Mg2Si (pre-eutectic and eutectic) and eutectic Al in the Al-Si microconstituent.
Flux Assisted Casting Preparation and Surface Property Evaluation of Aluminium Matrix Composites Reinforced with Carbide Nanoparticles
In the present effort, Aluminium Matrix Composites (AMCs) reinforced with submicron TiC and WC particles of 0.5 to 1 vol% content were produced through a casting based process assisted by both: (a) the use of K2TiF6 as a wetting agent in order to enhance particle incorporation into the molten matrix and (b) mechanical stirring to limit particle clustering. The produced composites are compared as far as their microstructure, wear and corrosion behaviour are concerned. Microstructurally-wise, an almost uniform particle distribution was achieved in both cases of particle reinforcement, characterized by clustered and isolated particles located mainly at the grain boundaries. Particle incorporation was kept at high levels suggesting the beneficial action of the K2TiF6 salt, whereas particle clustering was limited mainly due to mechanical stirring. Various intermetallic phases were formed as a result of both the inoculation by the K2TiF6 salt and the intensive reactivity of the ceramic phases with the molten matrix. The latter was mostly attributed to the ultra fine particle size. A eutectic microconstituent was also observed at the grain boundaries. Solidification front – particle interactions were found to also account for the final particle distribution and location. Sliding wear experiments revealed a beneficial action of the reinforcing phase on the wear response of the produced composites compared to that of the monolithic matrix. Surface oxidation, plastic deformation, crack formation and debris abrasive action were the main degradation features. Potentiodynamic polarization testing in Dilute Harrison's Solution (DHS) suggested similar corrosion mechanisms irrespectively of the type of the reinforcement phase. The performed analysis revealed localized corrosion effects mostly associated with the matrix alloy. Corrosion was largely associated with the eutectic microconstituent and the grain boundaries. Areas with a high concentration of sub-micron-particles had remained essentially free of corrosion signs.
A. LEKATOU, V. GOUSIA, A. EVANGELOU, Z. GACSI, P. BAUMLI, G. KAPTAY, A. SIMON
In this research, Al2O3-glass composites were prepared and investigated. To produce alumina-glass composites, alumina and glass cullet was used. Cullet in different size and amount was added to the alumina matrix, by applying two kinds of pressures. The glass components are chosen in order to the composites can be produced at lower temperatures with high strength and good electrical properties. During sintering, glass phase melts and surrounds the alumina particles. The effect of pressure and cullet size on the microstructure, thermal and mechanical properties of the composites was investigated.
D. LIPUSZ, B. GYÃ–RFFY, F. KRISTÃLY, Z. GÃCSI
Investigation of Mechanical Properties of Aramid Fiber Reinforced HDPE Composite
Aramid fiber has a wide application in several industries own to its extremely high mechanical and physical properties. High density polyethylene (HDPE) seems to be an inappropriate matrix alternative, because it is highly inert and hard to form a fiber-matrix interface. However, this property is unique in such application as liquid and gas storage or transportation. This study investigates production of an effective continuous aramid fiber reinforced HDPE composite. In order to improve fiber-matrix adhesion, maleic anhydride grafted polyethylene and ethylene-methyl acrylateglycidyl methacrylate terpolymer compatibilizers were applied as a tie-layer between matrix and fiber layers. Composite productions with compatibilizers were carried out on a laboratory scale press at 220°C and 3 minutes. Adhesive lap-shear bond strengths of obtained composites with/without tie layer were measured using the lap-shear tests. Tensile test were also applied to samples produced. Tensile strength values were compared with the lap-shear strength values. Mechanical test results were supported with SEM observations taken from the possible fiber-matrix interface regions and failure patterns observed on samples. Finally, it was found that both test results had same trends showing compatibilizer applications as tie-layer had improved the strength of HDPE composite.
Determination of the Effects of Recycling on Polyolefin Matrix Composites
Thermoplastic composites, especially polyolefin ones, could not display strength values as high as thermoset composites due to their incompatibility between fibrematrix interface. However, addition of compatibilizer could improve their mechanical performance nearly to the level of thermoset composites. Thus, applications and usages of thermoplastic composites were increased in recent years. This is the one of the reasons to take into consideration of recycling them. This study investigates the thermo-mechanical recycling of post-consumed E-glass fibre reinforced thermoplastic composites and their usage in similar to virgin chopped fibre reinforced composite materials. High density polyethylene (HDPE), a group of thermoplastic polymer, was reinforced with the 4 mm length chopped E-glass fibre. HDPE matrix composites, which contain 5 wt% of maleic anhydride based compatibilizer, were recycled by a shredder. Obtained flakes have been molded by a laboratory scale press. Recycled composites were remanufactured up to 8 times cycling. Mechanical and physical properties of produced composites have been characterized. Tensile strength, flexural strength, impact strength were determined through mechanical tests. Calcination test was carried out to expose the fibre content and sieve analysis was also applied to these. Also fibre distribution behaviors in virgin and recycled composites were observed by microscopic investigation and mechanical performance of composites discussed according to this aspect. Effect of recycling on composites was evaluated for each type of composite separately.
Developing Industrial Testing Methods for Screening the Off-Axis Performance of Alternative GRP Fibers
The composites industry faces a frequent laminate testing need due to the improvement of materials, quality control and supplier changes. For economical reasons, the industrial testing methods must be swift, inexpensive and rugged, yet give reliable data on the essential qualities. In the wind turbine blade industry, these qualities include laminate off-axis fatigue properties, whose traditional testing methods cost considerable amounts of time and money. In this study, the laminate offaxis properties testing methods are streamlined to yield sufficiently reliable data for choosing the best fiber product out of several candidates to the specified application.
Uniaxial Tests of Limp Elastic Multi-Layer Materials
The paper presents the effect of the width of a specimen cut out from coated fabric subjected to uniaxial tensile on the transverse deformation of the material. Tests were carried out for both uniform and split into three strips samples with a width of 100 mm according to the ISO 1421:1998 standard. The tests were carried out to verify the method of determining the mechanical properties of coated fabrics as supplied, based on the hypoelastic constitutive relation. The method is still being developed.
Multi-Line-Beam with Variable Kinematic Models for the Analysis of Composite Structures
In the finite element analysis of composite structures, it is a common practice to use different formulations in different sub-regions of the problem domain. In the present work, the Carrera Unified Formulation (CUF) is used to develop variable kinematic structural models. CUF is a higher-order, one-dimensional (1D), finite element formulation which was recently introduced by the first author. By exploiting the hierarchical characteristics of the CUF, a multi-line approach is developed straightforwardly and used for the analysis of a multilayered structure. In the multiline method, 1D refined finite elements with different order of expansion over the cross-sectional plane are employed in different regions of the domain of the structure. Lagrange multipliers are used to ‘’mix’’ different order elements. Constraints are imposed on displacement variables at a number of points (‘’connection points’’) whose location over the interface boundaries is a parameter of the method. The accuracy of the proposed method is verified both through published literature and through finite element solutions using the commercial code MSC/NASTRAN.
Structural Optimization Study of Laminated Axisymmetric Shells and Plates
This article presents buckling forms and structural optimization of rectangular plates, cylindrical shells and cylindrical shells with domed heads The analysis shows that the proposal of new discrete design variables seems to be effective in the case as buckling loads are defined in the analytical manner.
Microstructural Characterisation of Jute/Epoxy Quasi-Unidirectional Composites
A novel image analysis technique has been developed to permit the analysis and quantification of features in bio-based composite microstructures.
Numerical Homogenization of a Folded Sandwich Core
This document describes the homogenization of a folded sandwich core. By using a numerical homogenization concept the components of the elasticity tensor of the foldcore continuum are determined. The foldcore exhibits an effective orthotropic behaviour with the particularity that it can be auxetic.
Creep of Epoxy-Clay Nanocomposite at the FRP Interface
Creep of epoxy at the fiber reinforced polymer (FRP) interface can result in offloading of the FRP and inefficient structural strengthening. When the FRP strengthened structure is subjected to sustained loads, creep of epoxy shall be carefully considered and controlled. This paper examines the possible control of creep of epoxy at the FRP interface using nanoclay. In this paper, creep behavior of epoxy-clay nanocomposite at the FRP-steel interface was experimentally measured using double lap shear test. The test involved loading two carbon fibers reinforced polymers laminates (CFRP) bonded to two sides of steel blocks using epoxy under sustained loads and measuring shear creep. The significance of nanoclay loadings of 4% and 10% by weight of epoxy resin on creep behavior at the epoxy-FRP interface was measured. The experiments showed nanoclay loading to have a significant effect on epoxy creep at the FRP-steel interface. A threshold of nanoclay content beyond which nanoclay can limit epoxy creep seems to exist. Microstructure characterization tests were performed to explain the observed effect of nanoclay on creep of epoxy at the FRP interface. Transmission electron microscope (TEM), X-ray diffraction analysis (XRD), 29Si nuclear magnetic resonance (29Si-NMR) and differential scanning calorimetry (DSC) measurements were performed. These measurements showed that nanoclay intercalation rather than exfoliation is necessary to control epoxy creep.
Epoxy Matrix Magnetic Composites with Enhanced Thermal Conductivity
In this research, epoxy matrix composites filled with hard magnetic material namely strontium ferrite have been investigated. Samples with different content of filler were prepared both with and without presence of the external magnetic field during manufacturing step in order acquire isotropic and anisotropic distribution of the filler respectively. Appropriate orientation of magnetic field was used to obtain samples with parallel or perpendicular alignment of the filler to the field. Thermal conductivity was studied as the function of temperature for selected set of samples. As it was expected, the orientation of filler along the direction of applied magnetic field results in enhancement of thermal conductivity, as the conductive paths of filler are more likely to create. XRD structural characterisation and microscopic observations of filler and composites have been presented. The model predictions were analysed and validated with experimental results. Analysis of thermal conductivity for the composites and its constituents as well as its temperature dependence seems to be a promising method for determination of its mechanism, including the role of interfaces in particular.
GASKA, A. RYBAK, C. KAPUSTA, G. KMITA, R. SEKUÅA
Vibrational Analysis of Aerospace Composite Components for Production Defects and Operating Damage Detection
Non-Destructive Testing of aircraft structures is of paramount relevance leading to key information regarding the structural characteristics and the residual life of a component. This paper is focused on the experimental and modeling activities related to vibrational analysis carried out on a typical aeronautical composite sample. A flap section of a regional aircraft has been studied applying the conventional tools of the modal analysis. The aeronautical component has been at first characterized in terms of natural frequencies and normal modes. Then it has been damaged using a drop tower that induced a controlled impact in the structural component. The vibrational analyses have been repeated and the normal modes in the two conditions have been compared. Then other approaches based on vibrational properties of the structures have been investigated to detect defect and damage.
SCARSELLI, A. MAFFEZZOLI, E. CASTORINI, A. TAURINO
NDE for Compression Loaded Composite Structures Using a Nonlinear Ultrasound Method
The work looked at determining a nonlinear ultrasound acoustic moment method for structures that are under high load and thus damage detection is more difficult. Previous work using acoustic moments have focused mainly on the health of adhesive joints and bonds. This work focuses on developing a methodology that uses both the linear acoustic moment and nonlinear acoustic moments of a given signal to help determine the damage present in a compression loaded specimen. A rig was used that allowed the adjustment of the pressure between two flat composite plates, while the contact between the two plates was used to simulate a composite joint with a kissing bond defect. Two piezoelectric sensors were used to send and receive the input and output signals. The acoustic moment was based on the integral of the Power Spectral Density (PSD) function and tests were conducted in three steps: (i) initially the 1st, 2nd and 3rd harmonics of the output PSD function were located, (ii) then they were isolated by filtering out other noise and responses thus leaving the peaks of the respective harmonics, and (iii) finally the respective harmonics were evaluated using integration, giving the respective acoustic moments. The results showed that nonlinear acoustic moments (2nd and 3rd harmonic responses) responded more adversely to increases in load than that of the linear acoustic moment (1st harmonic). This was clearly seen as the rate of decrease in the above described compression loaded system for the nonlinear acoustic moments as load increased, was larger than that of the linear acoustic moment. The work provides a solid platform for the proposed acoustic moment method suggested, and shows that the relationship between the linear response and the conversion of energy to generate the nonlinear responses can provide useful information about damage in compression loaded systems.
Development of a Fast Inspection System for Aerospace Composite Materials—The IntACom Project
IntACom is a 3 year project that will develop a prototype robotic scanning system for the rapid, automated Non-Destructive Testing of complex geometry composite components for the aerospace industry. The objective is to achieve a four-fold increase in the throughput of components under test by increased automation of the inspection process through improvements to data presentation and assisted flaw detection. This paper discusses the approach adopted and the progress to date.
I. NICHOLSON, D. YAN, B. WRIGHT, C. MINEO
Infrared Thermography to Detect Delamination and Porosity in Carbon/Epoxy
Infrared thermography (IRT) has already proved its capability to deal with several types of defects buried in different types of composite materials and now is amongst the aeronautical standards. However, the real use of infrared thermography is still somehow limited, needing additional tests and validation. The aim of this work is to contribute to the assessment of infrared thermography as a technique to be used to both estimate the porosity amount and distribution in a carbon/epoxy material as well as to detect a thin delamination in presence of porosity. The detection of a defect with infrared thermography is based on the thermal contrast induced by such a defect, or k l u b d n u o s e h t o t t c e p s e r h t i w t c e f e d e h t f o s e i t r e p o r p l a m r e h t t n e r e f f i d e h t y b r e t t e bm aterial. The presence of porosity means a relatively high percentage of gases entrapped within the material. Besides, a delamination practically means a volume of gases (generally a thin layer) at the interface fiber/fiber, or fiber/matrix. Therefore, the resultant differences in thermal characteristics between the defect and the bulk material are very small which reduces the possibility of the defect to be distinguished. Then, this work wants to investigate whether infrared thermography can be used to detect delamination in such uneasy circumstances. Two different procedures are pursued: flash thermography through local variation of the thermal diffusivity, and lockin thermography through local variation of the phase angle.
C. MEOLA, S. BOCCARDI, F. DE FALCO, V. GRASSO, G. M. CARLOMAGNO
A Comparison Between Ultrasonic Testing and Lockin Thermography in Nondestructive Evaluation of Porous CFRP Plates
The introduction of composite materials in the aeronautical industry, as substitute to metals, for fabrication of primary and secondary structural parts, has fulfilled two main requirements. In fact, on one side, composites supply a response to the increasing need of favorable stiffness to weight ratio and, on the other side, they represent the best solution to the requirements of producing even more complex structural parts by starting from the design of the row material. As a main drawback, composites, and specifically carbon fibers reinforced polymers (CFRP), are strongly heterogeneous being made by long carbon fibers kept together by a polymeric matrix. So, they are characterized by directional mechanical properties and, due to the complex production processes, they are vulnerable to the formation of specific defects since their fabrication. Among the main manufacturing defects, porosity is one of the most difficult to be taken under control, while it has detrimental effects on the mechanical properties of the final component. On the other hand, its evaluation is rather difficult. In this work, the extreme case of a delaminated CFRP plate affected also by porosity is addressed. To this end, several groups of coupons are manufactured with induced in each group a different amount of porosity within their structure, and with also an artificial inclusion interleaved in the lamination sequence to simulate a local delamination. Then, the aim of the present work is to compare the effectiveness of two techniques: Ultrasonic Testing (UT) and Lock-In Thermography (LT) in the detection of delamination in such a difficult environment. The obtained data highlight a different capability of the two techniques to detect defects, also in the light of a data fusion.
Bending of Beams Externally Reinforced with TRC and CFRP Monitored by DIC and AE
Strengthening and repairing existing reinforced concrete structures is often more economical and sustainable than rebuilding them. The most commonly used technique, externally bonded Carbon Fibre Reinforced Polymers (CFRP), does not answer the need for a temperature resistant, fire safe and economical solution. High performance glass fibre Textile Reinforced Cements (TRC) can offer an answer to these drawbacks. A validation of this TRC technique against the existing one of CFRP is still needed. The Digital Image Correlation (DIC) and Acoustic Emission (AE) measuring techniques are applied to monitor the bending, cracking and failure behaviour of a reference beam, a beam with CFRP external reinforcement and a precracked and non-precracked TRC external reinforced beam. Four-point bending tests indicate the successful complementary use of DIC and AE and prove that TRC as an external reinforcement for concrete beams actually works.
A Promising Method for the Detection of Subsurface Defects in Impacted Composite Materials Made by Natural Fibers
In this paper, infrared vision and optical nondestructive testing (NDT) techniques were applied for the evaluation of emerging defects after impacts in composite materials made by natural fibers. The samples were manufactured using wool and jute fibers. Pulsed thermography (PT) and square pulsed thermography (SPT) were used as stimulated heating procedures, while two algorithms, named principal component thermography (PCT) and pulse phase thermography (PPT), were applied in order to enhance the acquired thermographic data. For comparison purposes, near-infrared reflectography (NIRR) and transmittography (NIRT), as well as laser speckle imaging techniques, were also included. Additionally, ultraviolet (UV) imaging technique was used on the samples both as complementary approach and as reference for the future inspections. Two particular zones highlighted by the latter technique were characterized using an XRF spectrophotometer which revealed a reverse concentration of the Al, Si and Cl elements. This work can be considered as an innovative approach in the characterization of eco-friendly laminates after an impact loading.
N. AVDELIDIS, C. IBARRA-CASTANEDO, P. THEODORAKEAS, A. BENDADA, D. PAOLETTI, M. KOUI, X. M
Property Evaluation of Surface Modified MWCNTs Reinforced Polymer Composites Under Low Earth Orbit Environment Conditions
In this paper, the property of multi-walled carbon nanotubes (MWCNTs) reinforced epoxy polymer (CNRP) composites exposed to low earth orbit (LEO) environment are investigated. In order to study tailored CNRP, a surface modification of MWCNTs was tuned to improve interfacial bonding between the nanotubes and the matrix. The surface modification of MWCNTs had been carried out using multifunctional silanes (3-APTES) being popular for the surface treatment of MWCNTs. The corresponding moieties were characterized by Fourier Transform Infrared Spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface modified multiwalled carbon nanotubes reinforced polymer composites were prepared by solution mixing method using mechanical/physical approaches to disperse homogeneously the MWCNTs into the polymer matrix. The sets of specimen series were tested in accelerated LEO simulated space environment. The synergistic environmental factors of the used ground simulation systems were the high vacuum, atomic oxygen (AO), ultraviolet (UV) radiation and thermal cycling. The material properties of CNRP composites before/after exposed to LEO space environment was evaluated through the measurement of mass loss against temperature variation, coefficient of thermal expansion (CTE), total mass loss (TML), tensile strength, thermal emissivity (ε). The results indicate that the surface modification of MWCNTs can reduce mechanical properties degradation and enhance thermal stability of CNRP composites with very low MWCNTs content exposed to LEO environment.
Innovative Highly Out-of-Plane Thermally Conductive Fibre Reinforced Plastic
The advantages of Fibre Reinforced Plastics (FRP) over conventional metallic materials are their lightweight, high strength and non-corrosive properties. Nevertheless, one major disadvantage is the low out-of-plane thermal conductivity (TC) of FRP which limits their application where heat has to be dissipated through the thickness such as heat exchangers or electronic enclosures. Research in the last years at the Institut für Textiltechnik (ITA) of RWTH Aachen University, Germany, has shown that the TC of FRP can be increased one order and more using ultra high modulus pitch-based carbon fibres. These fibres have an axial TC in the range between 120 and 900 Wm-1K-1 whereas copper – one of the highest thermally conductive materials – has one of 400 Wm-1K-1. Unfortunately the ultrahigh modulus of these fibres comes along with very high brittleness which hinders the use in many textile processes. Nevertheless, ITA has developed processes to manufacture composite parts based on 2D and 3D preforms as well as on 2D and 3D prepregs [1]. An innovative invention from ITA increases the out-of-plane TC of FRP from below 1 Wm-1K-1 to 26 Wm-1K-1 using pitch-based carbon fibres. The clue is the integration of the highly brittle pitch-based carbon fibres with an E-modulus of 950 GPa into a honey comb structure. Hence, 100 % of the fibres can be oriented in out-of-plane direction to guide heat from one side to the other. The invention is under patent process.
Multifunctional SMA Reinforced Composites for SHM and De-Icing
During the last decade Shape Memory Alloys based composites have attracted the attention of a large number of researchers because of the great benefits that they could provide to traditional laminates in terms of mechanical properties enhancement. Indeed, the research to date has tended to focus more on the structural properties of such systems rather than on the non-structural features that a network of SMA network is able to activate. This work is focused on the study of the SHM/NDT feature of a multifunctional composite obtained embedding a hybrid network of NiTi wires within the structure of a CFRP. The multifunctionality of such materials relies on the possibility to exploit the electro-thermal properties of the SMA to localize potential internal damages within a CFRP laminate, by measuring the variation in the apparent temperature on the composite surface via an in-situ active thermography that does not need external heaters or lamps to generate the thermal stimulation required for the analysis. The sensitivity of this technique was evaluated by testing several hybrid samples with delaminations characterized by increasing severity positioned a different distances from the top surface and at different depths within the laminate. Moreover, the presence an embedded heating source has been also tested as a promising ice protection system for composite aerostructures due to its rapidity and effectiveness.
Single-Walled Carbon Nanotube-Enabled Conductive Adhesives for Aerospace Applications
Single-walled carbon nanotubes (SWCNTs) were incorporated at low loading (up to ~1 wt%) into an unfilled adhesive to impart electrical conductivity while maintaining the structural bonding capability of the baseline, aerospace-grade adhesive. Conductivities as high as 10-1 S m-1 and typically ~ 10-3 S m-1 were achieved for 1 wt% SWCNT-adhesives. The structural bonding performance of composite-to-composite joints, evaluated in lapshear and peel tests, was reasonably maintained for adhesives containing 0.5 wt% and 1 wt% SWCNTs.
B. ASHRAFI, Y. MARTINEZ-RUBI, C. T. KINGSTON, Y. ZHANG, A. JOHNSTON, B. SIMARD
Impact Source Localization on a Helicopter Tail Rotor Blade
This paper illustrates an in-situ Structural Health Monitoring System for the localization of the impact source on a helicopter composite tail rotor blade. This technique, based on the Inverse Filtering process, is applied to a number of waveforms recorded by a number of passive piezoelectric transducers containing the impulse response of the medium. Unlike other ultrasonic impact localization methods, the present technique allows obtaining the optimal focalization of the impact point by taking advantage of multiple linear scattering and a small number of receiver sensors. The impact localization results shows that the location of the impact point could be achieved with a high level of accuracy in any point of the structure as long as a high number of information from the signal spectrum was contained in the recorded waveforms.
Strain Measurements of a Sailboat Bowsprit Cured in Autoclave by Means of Embedded Fibre Bragg Gratings
Acrylate-coated Fibre Bragg Gratings (FBGs) were embedded in a sailing boat bowsprit tubular section manufactured using vacuum bagging process in autoclave with the aim of reliably measuring strains under realistic loading conditions. In order to establish an efficient integration procedure, flat tensile specimens with embedded acrylate-coated fibres and FBGs were firstly produced under different processing conditions, using advanced composite material employed in the maritime industry. Optical losses and performance of the sensors embedded in the specimens were evaluated using Optical Time Domain Reflectometry and through comparison with standard electrical strain gages. Information obtained in this way was then used for the production of a sailboat bowsprit with a rectangular hollow section and an array of gratings embedded between the inner last plies. In order to assess the quality of the optical fibre sensors results, the bowsprit was subjected to bending tests and the measured strain values were compared to the analytical data and the experimental measurements obtained from electrical strain gages. Results are very encouraging but reveal that great attention must be devoted to the integration process and especially the in-situ calibration of the FBG sensors.
Deflection Monitoring of a Composite Blade Using a Modal Approach Based Shape Estimation Algorithm with FBG Sensors
Real-time deflection monitoring of a composite wind turbine blade was accomplished using the shape estimation algorithm with modal approach and strain data from embedded fiber Bragg grating (FBG) sensors. The finite element model of the composite wind turbine blade was created and the displacement-strain transformation (DST) matrix on the basis of the modal approach was obtained. The locations of the nine FBG strain sensors were optimized by minimizing the condition number of the displacement-strain transformation matrix. The deflection-monitoring test of the 11m span composite blade was conducted to verify the shape reconstruction algorithm and applicability of the FBG sensors in structural condition monitoring. The estimated shapes measured by embedded Bragg grating sensors are compared with the directly captured deflection shapes measured by stereo pattern recognition (SPR) cameras. The results confirm very close agreement showing the potentials of the proposed shape estimation technique using arrayed Bragg grating sensors.
Sepiolite/Silicone Sealants for Shipbuilding
Enhancement of fire behavior indeed represents a challenging issue for many materials and particularly for polymers. In this work, the fire performance of a commercial silicone sealant commonly used in shipbuilding industry was investigated. The effects of inorganic fillers were studied by thermo-gravimetry analysis (TGA) and micro-calorimetry (MCC). The use of these techniques, TGA and MCC, allowed for the creation of small batch of materials and corresponding formulation as compared to the kilogram sample needed for cone calorimeter testing. Results shown slightly variation of the total heat released rate and corresponding peak temperature, while a significant change in specific heat release capacity measured for the highest sepiolite percentage, degradation and flammability behavior due to the inorganic content.
F. D’URSO, A. PULLARA, M. CODDA, E. AMENDOLA, A. BORRIELLO
Processing Routes for Achieving MultiFunctionality in Reinforced Polymers and Composite Structures
Abstract of a paper submitted for oral presentation on the 9th International Conference on Composite Science and Technology, held 24-26 April 2013 in Sorrento, Italy
A. A. ALMAJID, A. NOLL, N. KNÃ–R, X.-Q. PEI, Z. RASHEVA, L. SOROCHYNSKA
Deformation and Damage in Fabric-reinforced Composites Under Bending
Verifying Molecular Model of Montmorillonite Nanocomposites
The density functional simulations (DFT) have been used to calculate elastic properties of montmorillonite clay platelets. A fully populated stiffness tensor has been calculated and all orthotropic elastic constants, for a first time, have been derived. The same model system and simulation parameters were used to predict Raman spectra which favorably compare with experimental data. The interfacial properties have been determined running molecular dynamics simulations with the force field which correctly predicts platelets spacing and infrared spectra of clay platelets.
Impact Characterization Diagram for Damage Resistance/Tolerance in Composite Structures
This paper presents preliminary work on the utility of a characterization diagram in impact damage tolerance studies for composite structures. By placing the impact response on the diagram useful information on the type of response and damage could be deducted prior to running experiments. It is expected that this methodology could be a very powerful tool to designers and experimentalists who work in the area of commissioning composite structures for damage resistance and tolerance.
In-Mould Gel-Coating for Polymer Composites
Steady-State Debond Growth Along Broken Fibers in Unidirectional Composites During Cyclic Loading
Several regions with different governing failure mechanisms may be distinguished analyzing axial tension-tension cyclic loading of unidirectional (UD) composite. At high loads multiple fiber fracture takes place during the first loading cycle. The relative number of broken fibers depends on the maximum stress and can be estimated assuming that the fiber strength is a statistical property following Weibull distribution. Multiple fiber fracture (fragmentation) is possible because the load is transferred into the broken fiber through the interface. In cyclic loading with constant amplitude we usually assume that fibers do not experience fatigue and all fiber breaks occur during the first cycle. During the following cyclic loading debonds start to grow along the fiber/matrix interface and this is the main mode of damage progression analyzed in this paper. The extensive debonding reduces the load borne by the broken fiber causing new fiber breaks and connecting the multiple fiber breaks, finally leading to catastrophic rupture of the UD composite. Hence, understanding of the debond growth process in fatigue is crucial for fatigue life analysis in this load region.
The Reinforcement of Nanocomposites with Graphene Oxide
The mechanisms of reinforcement of nanocomposites with graphene oxide are explored and the prospects of using the material in engineering applications are discussed.
Bioresorbable Composite Bone Fracture Repair Plates: Manufacture and Characterisation
This study reports on Bioresorbable composites manufactured using PLA as matrix and phosphate-based glass fibres as reinforcement. Composites were manufactured with varying volume fraction (from 25% - 45%) and mechanically tested.
N. HAN, A. QURESHI, A. PARSONS, C. SCOTCHFORD, B. SCAMMELL, C. RUDD
Effect of Curing Conditions on Mechanical Properties and Chemical Shrinkage in Polymers
Micromechanical Modeling of Semi-Crystalline Polymer Nanocomposites
H. POURIAYEVALI, CB. HE, D. W. C. CHEONG, V. P. W. SHIM
Silica Based Shear Thickening Fluids (STFs) and Their Composites
Effect of Compatibilizer on Mechanical and Physical Properties of Green Composites Based on High Density Polyethylene and Date Palm Fiber
Date palm leaves and wood are common wastes in the middle east. These natural fibers can be used as additives for polymers to develop new desired properties; they also have important economic and environmental advantages. The major problem in the addition of the natural fiber to the polymer matrix is the poor interface between the hydrophilic lignocellulosic fiber and the hydrophobic polymer matrix. Compatibilizers are usually used to overcome this problem. This work is focusing on the effect of the date palm filler size and origin (leaf or trunk) from female (Ikhlas) on the high density polyethylene matrix. The following interfaces were used to compatibilize the matrix and the fillers: Polyethylene-co-methacrylic acid (PEMA), Polyethylene-graft-maleic anhydride (PEgMA) and Polyethylene-co-methacrylic acid zinc salt (PEMA-Zn) with 1, 2 and 3 wt.%. Morphologies of composites were carried out by Scanning Electron Microscope (SEM). The mechanical and thermal properties of different samples were evaluated by tensile and TGA apparatus respectively. Samples based on 1 wt.% PEMA shown the highest Young’s modulus This behavior is may due to the increase in the interfacial adhesion and dispersion of the palm fillers within the polymer matrix, and confirmed by SEM micrographs. Thermal stability as limited by the compatibilizers due to the low thermal stability of the natural fillers itself.
Influence of Maghemite in the Dissolution Profile of Cotrimoxazole Inserted into Nanocomposites of PLGA-PEG/Maghemite
C. I. SANTANA, R. CERRUTI, J. C. C. DA SILVA PINTO, F. G. DE SOUZA JUNIOR
Helicoidal Laminates for Energy Absorption
Amorphized Cellulose as Filler for Innovative Ecocomposites
R. AVOLIO, I. BONADIES, M. COCCA, E. DI PACE, M. E. ERRICO, G. GENTILE
Integrated Structures for Aerospace Applications Via Resin Transfer Molding
Toughness and Strength Performance of Hierarchical Composites
Fabrication and Characterization of Epoxy Nanocomposites with Graphenes
Present research analyzed the manufacturing, using high speed rotational stirring and calendering as dispersion methods, of epoxy resins nanodoped with variable contents graphene (from 0.5 to 3.0 wt. %) of different kinds of graphenes characterized by their different particle size and number of graphenic layers. Produced nanocomposites were structurally, thermal and thermomechanically characterized. Effects of processing variables and graphene structural characteristics on nanocomposite properties have been evaluated.
S. G. PROLONGO, R. MORICHE, M. SÃNCHEZ, A. UREÑA
Health Monitoring in Composite Materials Using Carbon Nanoreinforcement Networks
Multiscale composites have been fabricated using matrix doped with carbon nanotubes or fibres coated with a sizing agent that contained the nanoreinforcements. Mechanical tests were made, and the electrical resistance was measured simultaneously. Both methods demonstrated that these systems worked as stress/strain and damage sensors.
C. ROMÓN, A. JIMÉNEZ-SUÃREZ, M. CAMPO, J. RAMS, A. UREÑA
Thermal Degradation Modeling of a Composite Material
M. DAMIANO, M. ZARRELLI, M. GIORDANO, F. SCARAMUZZINO
Interaction of Vulcanization and Reinforcement of Nanoclay (MMT) and Cellulose II on Dynamic Property of NR Characterized by RPA2000
J. G. L. COSME, R. M. MARIANO, L. L. Y. VISCONTE, R. C. R. NUNES
Crosslink Density in Carboxylated Nitrile Rubber Nanocomposites
L. R. HONORATO, L. L. Y. VISCONTE, R. C. R. NUNES
Evaluation of Polymer Nanocomposite Degradation During Melt Processing
Hierarchical Patterning of Nanomaterials for In Situ Discretized Damage Sensing Applications
Conductive Concrete for Electromagnetic Shielding Applications
New Proton-Conducting PVA/Clay/Ionic Liquid Nanocomposite Membranes for Anhydrous Fuel Cells
Proton-conducting nanocomposite membranes based on poly(vinyl alcohol) (PVA), acid montmorilonitte (MMT-H+) and the protic ionic liquid (PIL) diethylmethylammonium trifluoromethanesulfonate ([Dema][TfOH]) were prepared. The [Dema][TfOH] incorporation effect on membrane properties such as proton conductivity was investigated. The structural features of nanocomposite membranes were studied by Small angle X-ray scattering (SAXS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) and correlated to the membranes properties.
Polyelectrolytes Based on Speek/TiO2 Nanocomposites for Direct Ethanol Fuel Cells Applications
Proton-conducting nanocomposite membranes consisting of poly(ether ether ketone) sulfonated (SPEEK) and titanium oxide (TiO2) were prepared by sol-gel technique. The TiO2 incorporation effect on membrane properties such as ethanol uptake, pervaporation and proton conductivity was investigated.
Finite Element Simulation of Different Failure Modes for Buckling-Restrained Braces Under Cyclic Loading
Onset of Fibre/Matrix Debonding on the Surface of Organic Matrix Composites Due to Thermo-Oxidation
M. GIGLIOTTI, M. C. LAFARIE-FRENOT, J. C. GRANDIDIER
Design Exploration Methodology for Ultra Thick Laminated Composites
Methodology for Lifetime Prediction of Glass/Polyamide 6-6 Safety Pieces in the Domestic Distribution Network of Drinking Water
A Multiaxial Fatigue Damage Model for Glass Fibre Reinforced Polymer in Seawater
Study of the Experimental Low Velocity Impact Phenomenon on Carbon Composites to Support Numerical Simulations
Low velocity impact tests were carried out on carbon fibre reinforced plastic laminates at complete penetration at different energy levels at the aim to investigate about the damage initiation and propagation. Some of the specimens were destined to CAI tests and the residual strength was evaluated. The laminates were fabricated by a new vacuum assisted technology labelled as “pulse infusionâ€. All the experimental results, after analysing, were used to assist the numerical simulation. By the comparison, good agreements were found.
F. CAPUTO, A. LANGELLA, V. LOPRESTO, A. RICCIO, M. ZARRELLI
Numerical Methods for the Study of the Impact Behaviour of Composite Laminates Reinforced with Basalt Fibre
Low velocity impact tests were carried out on composites reinforced by basalt fibres, up to complete penetration. Indentation tests at different energy levels were add at the experimental campaign, at the aim to investigate about the damage initiation and propagation. A simplified numerical procedure in LS-Dyna was studied to simulate the impact behaviour of the basalt laminates. By comparing the results, a good agreement was found.
Recent Developments in Non-Destructive Testing of CFRP Components Using Active Thermography
Self-Sensing Carbon Nanotube Composites: Synthesis and Characterization
This presentation highlights recent research in the development of multi-scale hybrid composites for applications for in situ self-sensing of mechanical and thermal loading in advanced fiber composites.
Carbon Nanotube Reinforced Composite Films on Aluminium Alloy
Interlaminar Fracture Behaviour and Mechanical Properties of MWCNT Filled Epoxy Fibre Reinforced Composites
A. MARTONE, M. GIORDANO, M. ZARRELLI, A. LANGELLA, V. ANTONUCCI
Effect of MWNT on Pan Thermal Stabilization
G. S. CHEBOTAEVA, A. N. OZERIN, V. G. SERGEEV
Thermal Aging of CFRP Composites for Marine and Aeronautical Applications
This paper provides an insight on the evolution of mechanical properties of CFRP materials for aeronautical and marine applications, when exposed to specific environmental conditions, i.e. cyclical variation of temperature. This study is carried out by means of the experimental characterization of static compression, three point bending and interlaminar shear, which generates results on fibers and matrix resistance and on the mechanical properties of the composite.