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.

High Strain‐Rate Material Model Validation for Laser Peening Simulation

“…To overcome these design and analysis challenges, physics‐based computational models have been developed [7–15]. In this approach, finite element (FE) analysis is used to simulate the LP process and resolve the induced plasticity and residual stresses.…”

Finite Element Analysis of Laser Peening of Thin Aluminum Structures

“…First used by Braisted and Brockman [21] to simulate single LP shots on semi-infinite bodies, FEA techniques have evolved significantly over the past decade as computer processing has become faster and multiprocessing environments have become mainstream. Recent FEA studies of note include the work of Ding and Ye [22], who used three-dimensional FEA to create detailed stress maps for LP steel; Ocaña et al [23], who developed a multi-shot FEA model capable of realistic LP simulation; Singh et al [24], who coupled FEA with numerical optimization; Brockman et al [25], who used a highly refined, fully three-dimensional model to study local variations in surface residual stresses arising from shot patterning; and Hasser et al [26], who developed a first-ever FEA capability for studying LP-induced surface roughness.…”

Downscaled Finite Element Modeling of Metal Targets for Surface Roughness Level under Pulsed Laser Irradiation

“…Ran et al [16] developed a FEM structural numerical model for laser shock peening, predicted the surface roughness by applying the computed results as inputs to analytical equations, and then compared them with the experimental outcomes. Hasser et al [17] developed a structural FEM model to investigate surface roughness effects in laser shock peening and simulated roughness, which was produced by displacing surface nodes using a statistical method.…”