Spatial Distribution Evolution of Residual Stress and Microstructure in Laser-Peen-Formed Plates.

Zheng Zhang,Wen Huang,Yongkang Zhang,Guoxin Lu

doi:10.3390/ma13163612

Abstract

Residual stress in structural components is crucial as it affects both service performance and safety. To investigate the evolution of residual stress in a laser-peen-formed panel, this study adopted two plate samples of thickness 3 and 9 mm instead of the conventional Almen strip. The two plates were peened with an identical energy density of 10.99 GW/cm2. The residual stress across the entire section was determined using a slitting method, and near-surface stress was then verified by X-ray diffraction. Furthermore, cross-sectional variation in hardness and microstructure were characterized to understand the residual stress evolution. The experimental results showed that different thicknesses resulted in distinct spatial distributions of residual stress. The 3-mm plate demonstrated a shallow (0.5 mm) and lower compressive stress magnitude (−270 MPa) compared with a deeper (1 mm) and higher compressive stress (−490 MPa) in the 9-mm plate. Further analysis revealed that the deformation compatibility during the forming process inevitably leads to a stress compensation effect on the peened side. The decrease in the depth and magnitude of the compressive residual stress in the thin plate was mainly attributed to low stiffness and large deflection.

Highlights

High-energy and nanosecond-pulse width laser irradiation can induce high-pressure shockwaves, which provide unique advantages in material processing, such as ultrahigh strain rate (106 /s), deep compressive stress (1–2 mm), and low work hardening [1]
Target geometry plays an important role in the evolution of residual stress and deformation contours during the peen forming process
Note that the range of bulk residual stress in the base plate is surface plotted extended to a depth of mm

Summary

Introduction

High-energy and nanosecond-pulse width laser irradiation can induce high-pressure shockwaves, which provide unique advantages in material processing, such as ultrahigh strain rate (106 /s), deep compressive stress (1–2 mm), and low work hardening [1]. Depending on the target areas (regional or complete) and usage of the induced deformation (which may be eliminated or utilized), researchers have developed new techniques of laser shock peening (LSP) [2] for critical region strengthening and laser peen forming (LPF) [3,4] in metal sheet contour forming. Target geometry plays an important role in the evolution of residual stress and deformation contours during the peen forming process. The geometrical thickness affects shockwave propagation and plastic strain distribution [8], which are causally related to the generation of a compressive stress field. For thin metal foil/film (micron-level thickness), the shockwave can penetrate the entire cross section and result in completely plastic deformation.

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