Simulation of Surface Roughness Effects on Residual Stress in Laser Shock Peening

Abstract

Laser peening (LP) has shown to be a viable method by which the fatigue life of metallic components can be extended. Although current commercial implementation of LP techniques has not developed much beyond a trial-and-error methodology to implement the process, researchers at several institutions have examined various parameters that affect residual stress fields induced by LP, using Finite Element Analysis (FEA) and semi-empirical eigenstrain methods. This research is a preliminary investigation of a potentially under-considered variable in laser peening — material surface roughness. The influence of surface roughness on laser peening has not previously been studied through finite element modeling. The main point of interest for this work is to discover the amount that surface roughness magnitude affects the residual stresses created by LP. The FEA models, used in the exploration of surface roughness effects, had a simulated roughness produced by displacing surface nodes a pre-determined distance orthogonal to the original, smooth model surface. The amount that each node was moved was based on Kernel Density Estimation (KDE), a statistical method used to quantify uncertainties in random variables according to non-standard probability distribution functions. The KDEs were created from surface-roughness measurements taken from three separate 6061-T6 aluminum tubes. Two separate roughness sample sets were tested at magnifications of 1×, 10×, and 20× times the measured average roughness (Ra). Each roughness magnitude was simulated at peening pressures of 2, 2.5 and 3 times the Hugonoit Elastic Limit (HEL) for Al6061-T6. The 10× and 20× magnitude roughness samples produced significant changes in residual stress components relative to a smooth model, for all pressure loadings.