A simplified plasticity model for multiaxial non-proportional cyclic loading

Cyclic plasticity constitutive equations are required in fatigue and fracture analysis for the quantification of the plastic zone at notches or during fatigue crack growth. This work describes a constitutive model that reproduces the behaviour of stabilized metals subjected to multiaxial cyclic loads. The model is based on the idea of distance in the stress space which is calculated with a metric tensor. This metric tensor is a material property and can be empirically determined. In addition, the flow rule employs another material property known as hardening modulus. Procedures to calculate these material properties from experimental data are developed for the non-proportional loading case. The model gives good results for complex loading histories both from the qualitative and quantitative point of view. It also predicts the stabilized stress values in 90 degrees out-of-phase tensile-torsion tests.