Non-Contact Stress Measurement Method of Acousto-Optical Based on Zero Group Velocity Lamb

The stress of wall panel straightly influences on the safety throughout service life. Conventional methods for aircraft structure health monitoring (SHM) have limited precision and lack effective automation. To address these limitations, this study proposes an ultrasonic characterization method based on zero group velocity (ZGV) Lamb waves for the precise evaluation of structural stress. An opto-acoustic coupled stress detection system was utilized to extract local acoustic vibration information from laser-irradiated surfaces. Furthermore, an algorithm based on synchrosqueezing transform is utilized to extract instantaneous frequency of the ZGV signal. To enhance the quality of the extracted time-frequency ridges, a sparse Bayesian optimizer (BO) was applied, constructing local Rényi entropy (RE) and a reconstruction quality factor (RQF) as joint optimization criteria, and the proposed algorithm is capable of adaptive time-frequency representation (TFR). The error of stress measurement is 3.4 MPa, the repeatability standard deviation is 0.8 MPa, underscoring its potential as a robust and automated solution for precision SHM, which provides a promising solution for real-time stress monitoring in aerospace structures.