The Effect of Work-Hardening and Residual Stress on the Fatigue Strength of Steel Wire

Abstract

Since it is difficult to separate the contribution of residual stress to the fatigue strength from those of other factors such as work-hardening or size effect, no ultimate conclusion has yet been drawn on the effect of residual stress on the fatigue strength. So, the present investigation was designed to clarify the effects of longitudinal residual stress and work-hardening produced by drawing or surface rolling on the fatigue limit and life under rotating bending of carbon steel wire.Two kinds of testing material were used in this study. One is 0.8% carbon piano wire drawn at various additional reduction, and the other is carbon tool steel surface-rolled after annealing.The distributions of longitudinal residual stress and hardness over the cross section were measured. And the tensile test and the fatigue test under rotating bending were carried out for each specimen.From these experiments, the following conclusions were obtained:(1) The relationship between the numder of cycles to failure N and the stress amplitude σ can be expressed asN=C/A-e-Bσ+mΔσB-nΔσrwhere ΔσB and Δσr are the changes in tensile strength and maximum longitudinal residual stress at outer layer of the specimen due to drawing or surface-rolling, respectively, and A, B, G, m and n are constants dependent upon the material and working conditions. The fatigue strength of a material received cold working can be calculated accurately by this equation.(2) The residual stress influences the fatigue limit and life considerably but its influence is in a much less degree than that of work-hardening, and their ratio is about 1:3.