36. VISCOPLASTIC_MODEL Namelistο
36.1. Overviewο
The VISCOPLASTIC_MODEL namelist defines the viscoplastic model to be used for a particular solid material phase in material stress-strain calculations. Two viscoplastic models are available: a mechanical threshold stress (MTS) model and a power law model. When no model is given for a solid material phase, it is modeled as a purely elastic material. The models specify a relation for the effective plastic strain rate Μas a function of temperature \(T\) and von Mises stress \(\sigma\). For more details on the models see the Truchas Physics and Algorithms manual. Briefly:
Power Law Model. In the simple power law model, the strain rate relation is
where A, n, Q, and R are parameters given by this namelist.
MTS Model. The MTS model uses the strain rate relation
where \(\dot{\epsilon_{0i}}\), \(\dot{g_{0i}}\), b, k, D, \(\mu_0\), \(T_0\), \(\sigma_i\), \(\sigma_a\), \(p_i\), and \(q_i\) are parameters given by this namelist. When \(\sigma \lt \sigma_a\) we instead use \(\dot{\epsilon} = K\sigma^5\), where K is chosen to give continuity with the previous relation at \(\sigma = \sigma_a\). And when \(\sigma - \sigma_a \gt \mu\sigma_i/\mu_0\) we take \(\dot{\epsilon} = \dot{\epsilon_{0i}}\).