Mean Stress Correction of S45C Carbon Steel Based on Crack Growth Concept (Proposal of Non-Closure Model)

Abstract

Influence of the tensile mean stress on fatigue life and fatigue limit was investigated for carbon steel. Uni-axial fatigue tests were conducted under stress and strain-controlled conditions at room temperature. The fatigue life and fatigue limit were reduced by applying the mean stress for the same stress amplitude. The fatigue life exhibited a better correlation with the strain range than with the stress amplitude. Increase in strain range caused by applying the mean stress correlated well with the decrease in the fatigue life. It was proposed that the mean stress effect on the fatigue life was brought about by the change in crack growth rate caused by applying the mean stress. The mean stress enhanced crack opening and accelerated the crack growth. The reduction in the fatigue limit was also brought about by the same effect. It was shown that the effective strain range considering crack closure effect gave good prediction of fatigue life and fatigue limit with and without the mean stress.