Near Surface Residual Stress Determination of Laser Shock Peening by Neutron Diffraction

Abstract

The study of the residual stress fields generated by the advanced surface treatment laser shock peening (LSP) requires a technique that can measure from the bulk to the surface of a material. The application of primary and secondary collimator optics for the monochromatic neutron beam, and minor experimental corrections allow very near surface measurements without the associated errors of the “surface effect”. The measurements reveal that LSP generates compressive in-plane residual stresses to a depth of 1 mm in Ti-6Al-4V plate. Maximum compression is located at the surface (−800 MPa) and the balancing tensile residual stresses (max. 200 MPa) are located 2 mm beneath the surface. The use of a secondary radial collimator allows the determination of diffraction peak width depth profiles, indicating plastic deformation caused by LSP of 1–2 mm.