Simulation and experimentation on the impact of step thickness and corner shape on the characteristics of higher-order mode cluster-guided waves

Recently, the use of Higher Order Mode Cluster (HOMC) guided waves (GW) for ultrasonic testing of pipes and plates has been proposed. However, the generation and stability of the HOMC-GW were influenced by changes in mode shape and dominant mode shifts, which occurred in response to variations in thickness or frequency-thickness (fd) during propagation. Therefore, the primary objective of this study is to examine how thickness changes and different corners (right angle shape, chamfer shape, and curve shape) impact the generation of HOMC-GW signals. A 2D FEA model was developed in ABAQUS to simulate HOMC-GW propagation on steel plates with different stepped thicknesses. The Fast Fourier Transform (FFT) method was used to convert the time domain to the frequency-wavenumber domain. The outcome witnessed that the mode shape of HOMC changes when propagating through a sample with varying thickness; it is based on the frequency-thickness value (fd). In addition, the reflection signal was influenced by corner shape, step height, and frequency-thickness (fd) values. At a low step height (2.5 mm) and an fd of 20 MHz-mm, the right-angle corner produced a 33.1% higher reflection signal than the curved shape corner. These findings help in selecting suitable surface transitions and fd values to reduce signal obstruction and enhance HOMC-GW propagation in nondestructive examination. Additionally, Quantitative Laser Ultrasound Visualization systems (QLUVs) were used to examine the simulation results, and the HOMC signal was successfully captured and compared with the simulations.