Test of the new implementation of the Johnson-Cook model in Autodyn

In the Autodyn code version 4.2 there is a new option for treating strain rate dependent constitutive models. This so-called visco-plastic correction is available for the Johnson-Cook model. In this report, we test this option on a simple problem, namely, a simulated tensile test. Transient numerical oscillations do occur. For resonable parameters, however, they are small and have short duration in the tested cases. We also compare the new option to a user implementation of the same constitutive model, where the implicit problem is solved by iteration. Autodyn is believed to use an approximation, a first order correction, for efficiency reasons. The user implementation produces smooth curves for the stresses.