A study on the mean stress relaxation behavior of 2124-T851 aluminum alloy during low-cycle fatigue at different strain ratios

Strain-controlled fatigue tests of 2124-T851 aluminum alloy were performed under four strain ratios, R = −1, −0.06, 0.06 and 0.5. The fatigue test results indicated that the mean stress relaxation occurred under R ≠ −1. The mean stress relaxation rate was dependent on both the strain amplitude and strain ratio. In addition, fatigue life decreased with increasing strain ratio, especially at smaller strain amplitudes, which was attributed to mean stress and its relaxation during cyclic loading. Finally, based on the quantitative analyses of the mean stress relaxation behavior, a modified empirical model that can predict the mean stress relaxation at different strain ratios during fatigue was developed. The empirical model was then incorporated into the strain-life relationship to reflect the mean stress relaxation effects on fatigue life.