Damage detection of defects using linear and nonlinear guided waves

Abstract

In the past few years, application of guided waves for damage detection has been a topic of significant interest for many studies. Conventional guided wave techniques have been widely used in industry and technology for material characterisation and quality assessment by making use of so called linear acoustic response of material. It generally results in modification of linear parameters of guided waves such as wave amplitude, wave velocity, wave mode, and wave reflection and transmission. However, conventional guided wave techniques rely on baseline data known as the major linear guided wave techniques culprit. Among all guided wave techniques, nonlinear guided wave has been known as a promising baseline free approach, which offers enhanced reliability and practicability for damage detection. However, understanding of nonlinear guided waves is of essential importance for detecting and localising defects in structures. The nonlinear approach to acoustic non-destructive testing (NDT) is concerned with nonlinear responses of the guided waves, which is inherently related to the frequency changes of the input signal. Nowadays, composite materials are widely used in structures due to their attractive properties such as higher stiffness to mass ratio and better corrosion resistance compared to metals. So far, most of studies on application of nonlinear guided waves have been dedicated to isotropic materials, such as aluminium and steel, whereas only a limited number of works have been carried out on application of nonlinear guided waves in anisotropic materials. Moreover, most of works in this area have focussed on classical nonlinearity raised from material nonlinearity whereas a limited number of researches have focused on non-classical nonlinearity raised from contact acoustic nonlinearity (CAN). This research deals with linear and non-classical nonlinear interaction of guided waves with defects in structures from both numerical and experimental prospective. The aim of this research is to investigate guided waves for damage detection and damage localisation by developing an advanced 3D explicit finite element model for predicting the interaction of guided waves with defects in isotropic and anisotropic material. The study first focuses on linear guided waves for damage detection and is expanded to nonlinear guided waves. Chapters 3 and 4 focus on linear guided waves whereas Chapters 5 and 6 focus on nonlinear guided waves. The numerical work has been carried by an advanced 3D explicit finite element code in ABAQUS v6.14. Verification of finite element models has been carried out by comprehensive experimental studies. The linear guided wave measurement has been carried out using high precision scanning laser Doppler vibrometer (Polytec PSV-400-3D-M) and nonlinear guided waves measurement has been captured using a computer controlled arbitrary waveform generator (NI PXI-5412) and a NI PXI-5105 digitizer. The data has been processed in time domain and frequency domain and time-frequency domain using Matlab. The results of this study provide an improved physical insight into linear and nonlinear guided waves techniques. The results show that guided waves can be used for detecting and locating damages in beams and plates. However, nonlinear guided wave technique is a better option as it does not rely on baseline data and is more sensitive to small damages than the linear guided waves. A nonlinear guided wave damage localisation technique is introduced in this study which can accurately detect and locate damages without relying on baseline data.