VISCOPLASTICITY BASED ON OVERSTRESS WITH A DIFFERENTIAL GROWTH LAW FOR THE EQUILIBRIUM STRESS

Two coupled, nonlinear differential equations are proposed for the modeling of the elastic and rate (time)-dependent inelastic behavior of structural metals in the absence of recovery and aging. The structure of the model is close to the unified theories but contains essential differences. The properties of the model are delineated by analytical means and numerical experiments. It is shown that the model reproduces almost elastic regions upon initial loading and in the unloading regions of the hysteresis loop. Under loading, unloading and reloading in strain control the model simulated the experimentally observed sharp transition from nearly elastic to inelastic behavior. These properties are essential for modeling mean stress effects in tension-tension strain cycling.