Internal Hole Defect Detection Based on Laser Ultrasonic Shear Wave

This study presents a method for detecting interior hole defects using atime-flight scattered-shear wave (S-wave) methodology. Additionally, a mathematical model is proposed to quantify the detected defects accurately. The proposed method, PSO-VMD, combines variational mode decomposition with a particle swarm optimization algorithm to extract the mode conversion signal of a defect S-wave from a complex laser ultrasonic detection signal. This method effectively enhances the S-wave mode conversion signal’s signal-to-noise ratio (SNR). An experimental system using noncontact laser ultrasonic B-scanning is constructed. The system employs fixed excitation and detection methods. Experimental verification is conducted to accurately detect and identify hole flaws inside steel samples, considering variations in burial depths and diameters. The experimental results show that the proposed techniques for detection and signal processing are capable of accurately identifying and measuring hole defects. The relative positional error, which includes both transverse distance and buried depth, is below 5%, while the relative quantitative error, specifically in terms of diameter, is below 8%.