The inelastic stress-strain response of a material subjected to complex loading must be known or estimated in order to predict the fatigue life of a component using many current multiaxial fatigue damage models. This paper presents stress-strain predictions obtained using two incremental plasticity algorithms for several nonproportional loading paths.
The two algorithms both employ von Mises yield surfaces with kinematic hardening. However, one algorithm translates a single yield surface within a stationary limit surface using the hardening rules specified by Mróz and invokes a radial return for neutral loading. The other algorithm translates multiple yield surfaces (or a field of plastic moduli) according to a modified Mróz hardening rule proposed by Garud with no neutral loading provision. The algorithms are used to predict stress histories that are compared with measured responses from strain-controlled tests on normalized 1045 thin-walled tubes. A variety of nonproportional load paths were investigated. In general, relatively good agreement between predicted and measured stress-strain response for the two algorithms was observed for application to multiaxial fatigue evaluation. Strengths and weaknesses of each model are discussed.