Two level fatigue loading (H-L) of MG alloys: micromechanic modeling VS. experiments

Abstract

A statistical micromechanic fatigue model shows some of the main features of macro fatigue behavior like S-N power law, endurance limit, Goodman diagram, etc. The model correlates micro statistical damage parameters to the macro behavior. The recursive evolution equation has been recently transformed to a nonlinear differential form, which enables a simple analytic solution. Using these results, a two level (H-L) fatigue loading case is modeled analytically, leading to a failure design formula which is based solely on the one level S-N data. Specifically, the model predicts a generalized “Miner type” behavior, which is controlled on the micro-level by the very basic strength dispersion factor of the microelements, and on the macro-level by the S-N power (slope). The proposed H-L predictions were tested by fatigue experiments on two Magnesium alloys (AZ31 and AM50). Results showed good correlation, in spite of the natural large scatter.