Correction for Microstructure Effect on Residual Stress Measurement of SR-FSW Joint with L_cr Wave

Correction method for microstructure effect on residual stress of self-reacting friction stir weld joint measured with longitudinal critically refracted wave was discussed in this study. Two longitudinal critically refracted wave transducers, the spacing between which was fixed, were used, then the acoustoelastic formula was optimized, and difference in time of flight between longitudinal critically refracted wave, which replaced propagation velocity as characteristic parameter for residual stress measurement, was determined by the cross correlation theory, at last the influence of microstructure on residual stress of self-reacting friction stir weld joint was solved. Results show that as stress increases, the deviation in difference in time of flight becomes obvious, and when stress reaches stress turning point, experimental result is not agreed with the acoustoelastic theory as stress increases further. Step length is an important factor for difference in time of flight, and one cycle is seen as optimal step length. For acoustoelastic coefficient, the value of nugget zone is biggest, and the value of (heat affected zone + thermal mechanical affected zone) is smallest, in addition, the value of advancing side is slightly bigger than that of retreating side. Finally, residual stress of self-reacting friction stir weld joint was corrected with longitudinal critically refracted wave, and the result is verified by hole-drilling.