Finite Element Simulation of Shot Peened Residual Stress Relaxation Under Low and High Cycle Fatigue Loadings

Author:  Hongyan Miao, Thierry Klotz, Dorian Delbergue, Martin Lévesque
Source:  ICSP-13
Doc ID:  2017100
Year of Publication:  2017
Abstract:  
Introduction: Shot peening is widely used in automobile and aerospace industries to improve fatigue properties of metallic materials. Shot peening results in: (1) Surface compressive residual stresses beneficial to fatigue resistance by preventing crack initiation and delaying crack propagation; (2) Surface plastic deformation which results in dislocation at the surface; (3) Surface hardening which increases local yield strength and therefore increases the resistance for further plastic deformation from mechanical loading; (4) Surface roughness which acts as stress concentrator and produces crack initiation. The compressive residual stress is one of the key factor for fatigue life improvement. However, residual stresses may relax during fatigue loading and therefore greatly reduce the benefit of shot peening. McClung [1] provided a broad and extensive literature review of the stability of residual stress. The redistribution and relaxation of residual stresses under static mechanical loading, cyclic loading, thermal exposure and crack extension have been investigated. Prevéy [2] revealed a strong dependence of the amount of relaxation on the degree of the cold working induced during surface treatment. Cold work is cumulative and increases with the intensity and coverage of shot peening. Conventional shot peening produces 10% to 50% cold work. In addition, different shot type may introduce different cold work and the depth of cold work increases with the increase of intensity [3].