Recent Advances in Nonlinear Ultrasonic Guided Wave Techniques for NDT & SHM

Abstract

The use of nonlinear ultrasonic guided waves for nondestructive testing and structural health monitoring has drawn increasing concern. Higher harmonic generation (HHG) of ultrasonic guided wave propagation was firstly investigated and applied for damage assessment. The key concept for the HHG-based method is to find the “phase matching” modes to generate accumulate nonlinear components versus propagation distance, to improve the signal-to-noise ratio. The major difficulty with HHG method as the NDT technique lies in difficult to distinguish the material nonlinearity from the instrumental systems. In addition, HHG based nonlinear technique can only be used to evaluate the total nonlinearity over the region between transmitter and receiver. Subsequently, guided wave mixing (GWM) technique was proposed. GWM technique has some unique advantages, such as frequency selectivity, which can intentionally avoid receiving unexpected harmonic components induced by instrumental systems, as well as the feature of spatial selectivity of scanning wave mixing zone, which can be used to identify the local defect. Recently, static component generation (SCG) or quasi- static component (QSC) generation of guided wave pulse signals, was systematically explored and proposed. It is shown that the QSC based guided wave technique is an effective means to assess large structures with low attenuative effect. In addition, another breakthrough of nonlinear guided wave, is the expansive investigation on the acoustic nonlinear response of guided wave propagation in the topographic feature structures. The key concept is to build analytical model to find the modes with acoustic energy trapping effect in the feature region. The development of nonlinear feature guided waves (FGWs) technique provide a promising alternative for inspection of topographic feature region of complex structures.