Contribution of the Kinetics of Inelastic Deformations to the Summation of Fatigue Damage to Steels

Abstract

We propose a method for the evaluation of the accumulation of fatigue defects and variations of inelastic strains under cyclic loading with variable stress amplitudes. This method is based on the earlier developed model of ultimate exhaustion of cyclic plasticity. It is shown that, for materials with unstable inelastic deformations under cyclic loading, the fatigue damage does not obey the law of linear summation. We discovered a difference between the accumulation of fatigue defects in cyclically hardened and softened materials. This difference and nonlinearity are caused by the kinetics of inelastic deformations in different groups of materials. Hence, it is proposed to take this fact into account in estimating the degree of fatigue damage in order to decrease the computation error. In addition, we propose a scheme for the improvement of the results of evaluation of the total fatigue life under irregular loading by using the individual fatigue curves for the specimens with an aim of minimization of errors caused by the spread of experimental results.