Ultrasonic nondestructive testing of residual stress in parts formed by laser 3D printing

The residual stress in laser selective melting(SLM)forming parts strategies was studied in this paper, the residual stress in forming parts was detected by critical refraction longitudinal(L_CR)wave method, combined with the static load tensile test, acoustic elastic coefficients of SLM forming parts were calibrated. The results showed that when the tensile stress is less than the critical stress, with the increase of tensile stress, the propagation time difference of critical refraction longitudinal wave in SLM forming parts increases linearly. And the acoustic elastic coefficients of SLM forming parts manufactured using different scanning are different. Based on the stress-strain characteristics of SLM forming parts, the variation law of acoustic elastic of critical refraction wave was revealed. The reliability of this experiment was verified by the blind hole method. The results showed that the L_CR wave method was reliable in detecting residual stress. Compared with the blind hole method, L_CR wave method has the advantages of nondestructive and online testing.