High-energy synchrotron X-ray analysis of residual plastic strains induced in shot-peened steel plates

Abstract

Shot peening has long been recognized as a method for treating metal surfaces in order to improve their resistance to crack initiation and propagation. In view of shot-peening control, it would be useful if methods for direct measurement or estimation of residual stresses and depths of deformed layers were available. The focus of the present paper is on the presentation of high-energy synchrotron X-ray diffraction that allows better understanding of shot-peening residual strain profiles. Furthermore, it attempts to show that considerable elucidation of shot-peening effects can be attained if plastic strain profiles (eigenstrains) are considered, rather than residual stresses. Indeed, bending analysis shows that residual stresses depend on the sample geometry, and on the thickness in particular. In contrast, the experimental analysis presented in this paper suggests that the plastic strain profile induced in a particular material, on the other hand, is a function of the peening intensity alone and does not depend on the specimen thickness.

High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

“…In the former, the RSs are treated as mean biaxial stresses superimposed on the stress field produced by external loading, in the latter case, the RSs are included as R-ratio and crack closure effects. In the vast majority of cases, RSs are estimated through experimental measurements taken on flat unnotched coupons using laboratory incremental layer removal X-ray diffraction (XRD) [15,16], incremental blind hole drilling [17,18], synchrotron X-ray [19,20] or neutron diffraction [21].…”

Inverse Eigenstrain Analysis of the Effect of Non-uniform Sample Shape on the Residual Stress Due to Shot Peening

“…Shot peening has been considered and used in a variety of applications to improve the resistance to crack initiation and propagation in metallic components, enhancing service performance under fatigue loading and stress corrosion conditions [1][2][3][4][5][6][7][8]. In the course of the process, multiple progressive impact of a stream of shot particles on the surface leads to incremental local plastic deformation in the surface layers, while the layers below are not plastically deformed.…”

“…In the course of the process, multiple progressive impact of a stream of shot particles on the surface leads to incremental local plastic deformation in the surface layers, while the layers below are not plastically deformed. A number of publications have focused on establishing the complex relationship between the residual stress state arising following shot peening to the material properties, shot size, hardness, speed and angle of impact, and also the thickness of the workpiece [6][7][8][9][10]. Note here that considerable improvement in the understanding of shot-peening effects can be attained if plastic strain profiles (eigenstrains) are considered, rather than residual stresses [6].…”

“…A number of publications have focused on establishing the complex relationship between the residual stress state arising following shot peening to the material properties, shot size, hardness, speed and angle of impact, and also the thickness of the workpiece [6][7][8][9][10]. Note here that considerable improvement in the understanding of shot-peening effects can be attained if plastic strain profiles (eigenstrains) are considered, rather than residual stresses [6]. However, the relationship between the shot-peeninduced plastic strain distribution and the thickness/shape of a peened sample is still not well understood, particularly for samples of complex non-uniform shape.…”

“…could be termed 'extrinsic'), while experimental studies show that plastic strain distributions are a function of peening intensity, not of the thickness (i.e. could be termed 'intrinsic') [6,7]. In order to clarify the shot peening effects in non-uniformly shaped shot peened components, it is necessary to carry out the complete characterisation of elastic, plastic strain, and accordingly residual stress states.…”