Residual Stress Relaxation under Uniform and Gradient Applied Stresses

Shot peening (SP) is a commonly used surface treatment that imparts compressive residual stresses into the surface of components.  The shallow depth of compressive residual stresses, and the extensive plastic deformation associated with shot peening, has been overcome by modern approaches such as laser shock peening (LSP).  LSP surface treatment produces compressive residual stress magnitudes that are similar to SP, that extend 4-5 times deeper, and with less plastic deformation.  Retention of compressive surface residual stresses is necessary to retard initiation and growth of fatigue cracks under elevated temperature loading conditions.  This presentation compares the thermal relaxation behavior of SP and LSP residual stress profiles in a powder metal nickel-base superalloy (IN100) for a range of temperatures and exposure times.  Results indicate that the LSP processing retains a higher percentage of the initial (as processed) residual stress profile over that of SP.