Simulation of distortional hardening by generalizing a uniaxial model of finite strain viscoplasticity

In this paper we generalize a uniaxial model of finite strain viscoplasticity (proposed by Shutov and Kreißig) using the so-called concept of representative directions. As a result, a new three-dimensional phenomenological material model is obtained. The original model takes the nonlinear isotropic and kinematic hardening into account, but it does not cover the distortional hardening. Using a series of numerical computations we show that the isotropic and kinematic hardening is completely retained during the process of generalization. Moreover, the distortional hardening effects are automatically induced by the concept itself. This is demonstrated by simulating combined tension–torsion tests on thin-walled tubular specimens. Furthermore, the generalized material model is validated by a comparison with real experimental data concerning the shape of the yield surface. A good correspondence between the simulation results and the measurements is observed.