A Thermomechanically Consistent Constitutive Model for Polyoxymethylene

In this article tension, compression and torsion tests are presented using thin-walled tubes of polyoxymethylene (POM). These isothermal experiments show non-linear rate dependence, a tension–compression asymmetry and a pronounced relaxation behaviour. On the basis of the experiments carried out, a constitutive model of viscoplasticity with an equilibrium hysteresis in the small-strain regime is developed. Test calculations using finite elements based on the DAE approach show the capabilities of the thermomechanically consistent model. In particular, a very efficient stress algorithm can be derived which has no iteration on the element level. Moreover, it will be shown that time-adaptive finite elements could be of high importance if rate-dependent constitutive models are applied.