Stress measurement by laser grating based on laser ultrasonic technology

This paper introduces an innovative laser ultrasonic method designed for the assessment of surface stress. Specifically, a two-wave mixing interferometer is employed to detect Rayleigh waves generated by an Nd:YAG laser, offering a non-contact detection technique that mitigates errors introduced by coupling conditions. In contrast to pulse-line source excitation, a laser grating is proposed for ultrasound generation. This configuration avoids system biases in sound velocity measurement caused by attenuation and dispersion, leading to higher signal-to-noise ratio and increased stability. After data acquisition, a cross-correlation method is applied for the time-of-flight measurement. Upon determination of the acoustoelastic coefficient and ultrasonic velocity in a stress-free state, other aluminium blocks from the same batch are used for validation experiments. Subsequently, the temperature correction is implemented for measurement results and the corrected results exhibit a reduced uncertainty of less than 5 MPa, thus providing a reliable non-destructive solution for stress detection.