A Fatigue Approach to Design Shot-Peened Components Containing Surface Defect

Author:  E. Pessard, B. Gerin, F. Morel, C. Verdu
Source:  ICSP-13
Doc ID:  2017057
Year of Publication:  2017
Abstract:  
Introduction: Because fatigue crack initiation is usually located at the free surface of loaded component or specimen, a large number of articles in the literature focus on how surface integrity affects fatigue behavior. The term "surface integrity" includes both surface topography (i.e. roughness and local defects) and gradients in terms of residual stresses, hardening, microstructure, hardness, etc. which are often related. Surface integrity is very dependent on the manufacturing process being used, so studies on this subject usually focus on a specific process, such as machining [1-3], shot-peening [4,5], stamping [6] and punching [7]. The component studied in this paper is a hot-forged C70 steel connecting rod, which is shot-blasted after forging to clean off the forging scale, (shot-blasting is a process akin to shot-peening). During forging, scale can stick to the die surfaces which in turn introduces defects on the surface of forged components. Even if shot peening (or shot blasting) modifies the surface topography, it cannot remove the largest forging defects which can be up to several hundred micrometers in length Figure 1). The connecting rods therefore exhibit a particular surface integrity characterized by local surface defects, together with hardening and residual stress gradients generated by the shotblasting process.