Damage induced anisotropy of polycrystals under complex cyclic loadings

Abstract

Motivated by a low-cyclic fatigue micromechanical model proposed recently [1], qualitative and quantitative studies are performed emphasizing the concept of damage induced anisotropy. In this model, the plastic strain and local damage variables are examined at the crystallographic slip system scale for FCC metallic polycrystals. Determined at the macroscopic scale, the elastic behavior is initially assumed to be compressible and isotropic. The anisotropic damaged behavior, caused by activation/deactivation concept, is adopted using a fourth-order damage tensor at the overall scale. Accordingly, the overall behavior, notably the deactivation phase due to the microcracks closure under complex cyclic loadings, is of particular interest in the study. A host of plastic damaged behaviors of metallic polycrystals is predicted underlining the damage activation/deactivation effects on the multiaxial low-cyclic fatigue (LCF) behavior. Actually, the model is tested under strain- and stress-controlled conditions describing the effects of the loading complexity and the mean stress on the polycrystal LCF behavior. Finally, the model can successfully describe the LCF behavior of the Waspaloy at room temperature.