Effects of tensile elastic pre-deformation at different strain rates on the high-cycle fatigue behavior of SAE 1050 stee

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Hechuan Zhang First Geological Environment Survey Institute of Bureau of Geological and Mineral Resource Prospecting & Development of Henan Province, Zhengzhou, Henan 450001, People’s Republic of China

Lei Xu School of Materials Science and Engineering, Xihua University, Chengdu, Sichuan 610039, People’s Republic of China

Qingsong Zhang School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, People’s Republic of China (Received 5 April 2016; accepted 25 July 2016)

A series of characterization tests were performed to elucidate the high-cycle fatigue (HCF) behavior in SAE 1050 steel subjected to tensile elastic pre-deformation at different strain rates. In the pre-strained stage, the deformation was maintained constant at 0.16%, which was close to the low yield point at strain rates ranging from 10 5 s 1 to 102 s 1 . Although pre-deformation occurred entirely in the elastic regime, using different pre-straining rates resulted in the occurrence of heterogeneous microscopic strain at different sites and locations during subsequent fatigue tests. It was found that the effect of pre-straining rate on crack initiation and crack propagation was not monotonous and was influenced by the homogeneity of deformation within grain boundaries, the integrity of the boundary structure, and the fracture toughness. In addition, the rough set theory model was introduced for the attribute reduction of characteristic parameters and provided a scientific basis to establish the fatigue model. The model was able to effectively predict the lifetime of the process of HCF in pre-strained steel. Hence, the pre-straining rate should be an important boundary condition in further studies.

I. INTRODUCTION

SAE 1050 grade steels are often used in mechanical and electrical devices that are frequently exposed to high cyclic loading under service conditions. Hence, ensuring a good high-cycle fatigue (HCF) resistance is recognized as an essential prerequisite to their application.1,2 The HCF fracture process is generally divided into four stages: damage, fatigue crack initiation (FCI), fatigue crack propagation, and rapid fracture. The FCI stage represents the major portion of the fatigue lifetime in the HCF process.3 Makita et al.4 explained the process of damage from the perspective of redistribution of deformation. Gaier et al.5 assumed that fatigue damage was caused mainly by the stress normal to the critical plane. Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.288

Fatigue damage caused by HCF originates from the changes in the internal microstructure of the material, which result in a microscopic strain. The nature of HCF damage is a combination of mutually conflicting processes involving slip bands and obstacles and is usually related to the heterogeneity in microstructure, which generates local stress concentration effects and directly leads to fatigue failure. However, the site of the microstructure heterogeneity is det