A continuum damage mechanics-based approach for the high cycle fatigue behavior of metallic polycrystals

Polycrystalline elasto-plasticity models provide a general framework for investigating the effect of microstructural heterogeneities (e.g. grains, inclusions, pores) on the high cycle fatigue behavior of metallic materials. In this work, continuum damage mechanics is used to construct a set of constitutive relations to describe the progressive degradation of certain mechanical properties at the grain scale. The damage is considered to be coupled with the elastic behavior of the material. Special care is taken to include the anisotropic aspect of fatigue damage and the effect of intragranular internal stresses. The constitutive relations are then implemented within a self-consistent model to evaluate intergranular interactions. Finally, the model is used to investigate the high cycle fatigue behavior of polycrystalline copper. It is shown that the influence of certain loading conditions on the high cycle behavior is correctly reproduced. Specifically, the application of a mean shear stress does not result in an increase in damage; however, a mean normal stress is damaging. That is, a decrease in the fatigue resistance is predicted when the mean normal stress is increased.