Effect of surface roughness on laser ultrasonic guided wave defect detection for aluminum alloy plate

Laser ultrasonic testing is an advanced non-destructive testing technology for defect detection. However, the generation and propagation of laser ultrasonic guided wave (LUGW) is influenced by surface roughness, causing an impact on defect detection. To study the influence of surface roughness on LUGW propagation and defect detection, numerical simulation models are established for aluminum alloy plates. The simulation results show that the group velocity of A0 and S0 modes gradually decreases with increasing surface roughness, the amplitude of the S0 mode decreases in the roughness range of 0 μm to 3.2 μm, and the amplitude of the A0 mode decreases in the roughness range of 0 μm to 12.8 μm, and then increases. To verify that the established numerical simulation model can effectively predict the effect of surface roughness on LUGW propagation. A laser ultrasonic experimental detection system was built, and the scanning experiments were conducted on aluminum alloy specimens. The surface defects were imaged by the time-domain synthetic aperture focusing technique (T-SAFT). The experimental results show that the group velocity and amplitude of the A0 mode decrease with increasing surface roughness in the range of 0.61 μm to 3.82 μm, leading to reduced detection and localization accuracy.