General Constitutive Relations of Anorthotropic 6061-T6 Aluminum and Its Fatigue Life under Proportional and Non-Proportional Loadings

Abstract

Abstract Anisotropic constitutive relations with respect to the principal axes of an orthotropic solid are formulated using the macroscopic continuum plasticity theory of Shih and Lee. The general anisotropic constitutive relations are derived for predicting the plastic deformation behavior of a new material orientation. Straincontrolled cyclic tests were conducted along the 45° direction in the plane of the plate to verify the general anisotropic constitutive relations. The predictions agree very well with the experimental yield and plastic flow behavior. The axial-torsional coupling terms in the general constitutive relations are also determined and explained. The constitutive equations were used to predict the low-cycle fatigue life of this material under both proportional and non-proportional loadings. An anisotropic shear cracking model, developed earlier, provided a good prediction of the fatigue life of this material under both proportional and non-proportional loadings.