Benchmark of residual stress for ultrasonic nondestructive testing

Based on acoustoelasticsticity theory, critically refracted longitudinal (L_CR) wave was used to detect the residual stress in X70 steel. The method of fabrication and calibration for residual stress reference block was introduced and the detecting error brought by environmental temperature changes was corrected. The theoretical equation about the effect of temperature on residual stress detecting was analyzed. Low/high temperature test chambers and ultrasonic residual stress detecting equipment was used to detect the change of ultrasonic transit time difference, which caused by the temperature change. MATLAB second order polynomial was used to fit the experimental detecting results and fitted equation was obtained. The fitted equation was compensated to the system by software programming. The change of residual stress in reference block in two situations was compared. The results showed that temperature change had a large impact on the accuracy of ultrasonic residual stress detecting. The error of residual stress detecting can be effectively reduced by the temperature compensation modules. As result, the absolute precision of detection reaches ±10MPa.