Development of Damage Detection Techniques Using Guided Waves for Engineering Materials

Abstract

Guided waves (GWs) based damage detection techniques are vital for ensuring structural safety and are extensively applied in aerospace, mechanical, and civil engineering due to their high sensitivity and long-range scanning capabilities. However, two common challenges frequently arise in GWs damage detection for plate structures. The first challenge involves inspecting structural members that contain structural features like weld joints and edges, where defects commonly occur due to high stress concentration. These structural features have complex cross-sections, adding complexity to wave analysis and making damage detection a challenging task. The second challenge arises from inspecting structural elements made from anisotropic materials, such as timber and composite laminates. GW propagates in anisotropic materials can exhibit complex characteristics and require further investigation. The overarching aim of this thesis is to address these challenges by gaining insights into wave propagation characteristics influenced by irregular structural features such as welded joints and edges, as well as the presence of material anisotropy, as observed in timbers and composite laminates. The main body of the thesis comprises three journal papers, spanning from Chapter 2 to Chapter 4. Chapter 2 investigates on GW in a steel T-welded joint. A Rayleigh-like feature guided wave (FGW) has been identified propagating along the T-welded joint. This wave exhibits concentrated energy around the joint areas, enabling it to travel extensively along the joint with minimal attenuation. This characteristic makes it potentially valuable for inspecting common weld defects, such as cracks, along T-welded joints. Towards the end of this chapter, the defect's location is predicted using a time-of-flight method. Chapter 3 and Chapter 4 investigate GWs in anisotropic structural elements, including those with structural features. Chapter 3 investigates the propagation characteristics of GWs in timbers. The targeted damage is internal damages, which can be hardly visible from the timber surface. Both numerical and experimental studies are conducted to explore the interaction between GWs and timber internal damages. Chapter 4 delves into the anisotropy effect of edge waves concentrating at the edges of fiber-reinforced composite laminates. This chapter examines the dispersion relations of these edge waves on composite laminates with different stacking sequences. Numerical results are utilized to compare the displacement fields and mode shapes between the edge waves at the edges of composite laminates and those in isotropic materials. The findings reveal significant disparities in the displacement field and energy concentration of edge waves in comparison to their isotropic counterparts. These identified edge wave modes are then applied to detect edge delamination, using numerical simulations and experimental approaches.