Ultrasonic shear and longitudinal wave testing method of residual stress

Based on elastic theory, the ultrasonic nondestructive testing method of macroscopic residual stress distribution in plate thickness direction or bolt axial direction (hereinafter referred to as the z axis) is studied. A method of combining ultrasonic transverse wave and longitudinal wave to derive detecting formula is produced and pitch and catch mode is applied in the tensile test in order to reduce the influence on the stress testing accuracy of the detection principle, measured components' uneven thickness and measurement of stress coefficient. By experimental data fitting, the acoustoelasticity coefficient is re-calculated and is in place of stress coefficient. Afterwards, the software of ultrasonic testing residual stress in z axis direction is set up combined with interpolation and cross-correlation algorithm, then the detection system is also constructed. Tensile tests are conducted with the bolts in performance of A2-70, 4.8 and 8.8, whose lengths are 135 mm, 100 mm, 100 mm, respectively. Comparing the computation and detection of tensile stress, the results show that the absolute error limit is 20 MPa and the relative error of the test system is less than 25%. As residual stress increases, the relative error decreases. When the stress increases to over 100 MPa, the relative error is less than 5%. It shows that the testing system is practical.