On-line evaluation of yield strength in thin-walled specimens using laser ultrasonic technology

To prevent yield failure of thin-walled parts, an accurate on-line detection method is crucial. In this study, a laser ultrasonic technology (LUT) was proposed to inspect the acoustic behaviour of AISI type 304 stainless steel under tensile stress across time and frequency domain analysis. The specific acoustic parameters of LUT, including trough arrival time, trough amplitude difference, singular value decomposition entropy (SVDE), peak frequency, bandwidth, and energy distribution, exhibited distinctive characteristics at certain stress levels. Compared with traditional tensile tests, the yield strength determined by laser ultrasonic technology closely matched that obtained using the 0.5 % extension-under-load (EUL) method, with a slight difference of only 3.42 %. Additionally, through box plot analysis, the trough arrival time was confirmed as the optimal index for evaluating yield strength. These changes were further corroborated as corresponding to the yield stage through infrared thermal imaging technology. This research confirms that laser ultrasonic technology is an effective non-contact method for assessing yield strength, providing critical experimental and technical support for material analysis under operational conditions.