Measurement of Residual Stress Through a Shot Peened Surface Subjected to Successive Material Removal

Shot peening is a surface treatment process that is widely used across the aeroengine industry. The process introduces surface compressive residual stress, which enhances fatigue life through a retardation of early crack growth. Consequently, numerous aeroengine components are shot peened prior to entry into service. Traditionally, near surface residual stresses are measured using an X-ray diffraction (XRD) technique in combination with successive incremental material removal by electro-chemical polishing to obtain the depth profile of the stress distribution. Generally, no allowance is made for any redistribution of stress that may occur upon material removal. In this investigation, X-ray (XRD) and neutron diffraction (ND) measurements have been carried out on a shot peened nickel base superalloy (Inconel 718) specimen to accurately determine the extent of the redistribution. It is shown that progressive material removal can significantly relax the stresses generated by peening.