Measurement of Residual Stress Distribution in Laser-Shock Peened Ti-Alloy Using Hard Synchrotron X-Rays

Abstract

A plate of a Ti alloy, Ti-6Al-4V, with a thickness of 9mm was laser-shock peened. The distribution of the residual stress throughout the plate thickness was nondestructively measured with the transmission and reflection conditions of the strain scanning method using hard synchrotron X-rays of 70keV energy. The distributions of the in-plane and out-of-plane strains were measured by using the 004 and 112 diffractions of α-Ti phase. In-plane strains measured in two perpendicular directions were nearly identical, confirming the equi-biaxial state of residual stresses. The out-of-plane strain measured for the 112 diffraction agreed with the value calculated from out-of-plane strains based on isotropic elasticity, while that for the 004 diffraction was higher than the prediction. The discrepancy for the case of the 004 diffraction was caused by the intergranular strain due to plastic anisotropy. The use of the 112 diffraction was recommended for the stress measurement. The residual stress on the surface was compression of about −500MPa and the compression zone extended about 1.8mm below the surface. The distribution of the half-value-breadth also shows a large increase in the subsurface compression zone.