A model for the low cycle fatigue life prediction of discontinuously reinforced MMCs

An analytical model for predicting the crack initiation life of low cycle fatigue (LCF) of discontinuously reinforced metal matrix composites (DR-MMCs) has been proposed on the basis of Gibbs free energy law. The formation of a fatigue crack was considered to be associated with the reduction of the internal energy that could be expressed as a part of the area of the saturated hysteresis loop. The effects of the volume fraction Vf, cyclic strain hardening exponent n′ and cyclic strength coefficient K′ on the LCF fatigue crack initiation of DR-MMCs were analyzed at different levels of the plastic strain amplitude. While both the lower level of the plastic strain amplitude and the lower volume fraction of the reinforcement particles were found to increase the LCF crack initiation resistance, the effects of n′ and K′ were more complicated. Although a high n′ value or a low K′ value would lead to a longer LCF crack initiation life, their influence was interrelated. The theoretical predictions based on the proposed crack initiation model, in conjunction with Ding et al.'s [1] crack propagation model, were found to be in good agreement with the experimental data reported in the literature. Since both processes of the crack initiation and propagation have been considered, the accuracy of predicting the total LCF life of DR-MMCs was improved.