Yield, Plastic Flow, and Fatigue of an Orthotropic Material Under Biaxial Loadings

Yield, plastic flow, and low-cycle fatigue damage behavior of an orthotropic Al-6061-T6 plate were investigated. Anisotropic constitutive relations and multiaxial fatigue damage models of the material were obtained to predict its yield, plastic deformation, and low-cycle fatigue life under multiaxial loading conditions. Low-cycle fatigue tests were conducted along three orientations of the plate at room temperature under three loading conditions, uniaxial tension/compression, torsion, and combined tension/torsion in-phase, to verify the theoretical predictions. The theoretical yield functions and flow relations under combined tension/torsion loading condition agreed with experimental data reasonably well. Four multiaxial fatigue damage models were evaluated and used to predict the low-cycle fatigue life along the three orientations of the plate. A damage model based on the strain vector and an anisotropic shear cracking model gave better predictions than the effective strain and the plastic work models.