Surface stress detection of laser ultrasonic based on time-frequency analysis

Abstract The presence of residual stress can lower the service performance and service life of materials. However, traditional detection methods have limitations in aspects such as equipment dependence and detection dimensions. In response to the above problems, this paper presents a non-destructive detection method for laser ultrasonic surface stress based on time-frequency analysis. A laser ultrasonic detection system was established, and the laser ultrasonic surface wave signals under different stress states were extracted. The short-time Fourier transform (STFT) was introduced to conduct a time-frequency analysis of the surface wave signals. Through the two-dimensional energy distribution map in the time-frequency domain, the time-of-flight (TOF) of the signals in the time-frequency domain was extracted. The experimental results demonstrate that the TOF of the surface waves in the time-frequency domain exhibits a pronounced negative linear correlation with stress, and the stress within the material causes an increase in the propagation speed of the surface waves. Through two-dimensional positioning in the time-frequency domain, the mapping precision between the flight time and the stress variations can be enhanced, with the linear fitting coefficient R 2 reaching 0.99, validating the effectiveness of this method in the assessment of the surface stress of materials.