Effect of Shot Peening on Residual Stress Distribution and Microstructure Evolution of Artificially Defected 50CrV4 Stee
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Effect of Shot Peening on Residual Stress Distribution and Microstructure Evolution of Artificially Defected 50CrV4 Steel Simge Gencalp Irizalp, Nursen Saklakoglu, Fatih Baris, and Selda Kayral1 (Submitted April 7, 2020; in revised form September 25, 2020; Accepted October 4, 2020) The aim of this paper is to clarify the effects of shot peening on fatigue life and strain hardening behavior of spring steel samples containing artificial surface defect. Artificial defect acting as pre-cracks is introduced and the effects of this defect on the material surface and the distribution of residual stress away from the defect are investigated before and after shot peening. Shot peening has provided the following modifications on the surface: (1) homogenous compressive residual stress, (2) high dislocation density, (3) superficial strain hardening, (4) retained austenite reduction. In this paper, shot peening is applied to 50CrV4 steel and its effect on surface roughness, microhardness, surface residual stress, crystallite size and dislocation density calculation is determined and SEM observations are used to reveal the properties severely strainhardened layer. It can be shown that the shot peening can modify the crystallite size, however, the main effect is achieved by increasing the dislocation density and inducing the highly compressive residual stress. The effect of the surface modification to the 3-point bending fatigue life are analyzed.
Keywords
fatigue test, residual stress, shot peening, surface defect, surface strain-hardening
1. Introduction Fatigue is the most common mechanism of damage in mechanical structures that causes sudden breakdowns. For this reason, a lot of research has been made to examine the fatigue behavior of the materials. Many processes have been applied to increase the fatigue performance of the components. Shot peening (SP) is a mechanical surface treatment method that is widely used especially in the automotive and aerospace industries. SP is a process that improves the fatigue durability of components by modifying the surface (Ref 1). In this technique, the material surface is bombarded with small, hard, and high-speed spheres called shots, so localized inhomogeneous severe plastic deformation is induced at the specimen’s surface (Ref 2). The adjacent deeper material that borders around the localized plastic deformation produces surface compressive residual stress field (Ref 3, 4). Compressive residual stresses improve the fatigue strength by increasing the resistance to surface crack initiation and also propagation (Ref 5-7). Soady (Ref 8) presented the review of the effects of the SP process on surface roughness, strain hardening, and compressive residual stresses. It is stated that the benefits of compression type residual stresses and strain hardening resulting from SP are predominant over any detrimental effect on fatigue life, Simge Gencalp Irizalp, Nursen Saklakoglu, Fatih Baris, and Selda Kayral, Department of Mechanical Engineering, Celal Bayar Univers
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