Strain-rate effects in rheological models of inelastic response

Stress-strain response under constant and variable strain-rate is studied for selected models of inelastic behavior. The derived closed-form solutions for uniaxial loading enable simple evaluation of the strain-rate effects on the material response. The effect of an abrupt change of strain-rate is also examined. Non-Newtonian viscosity which decreases with an increasing strain-rate is incorporated in the analysis. Parabolic and hyperbolic hardening are used to describe the plastic response in monotonic loading. A three-dimensional generalization of an elastic-viscoplastic model is employed to study the stress relaxation in simple shear. A combined isotropic-kinematic hardening and the concept of overstress are used in the analysis. The unloading nonlinearity of the stress-strain curve is then discussed. (C) 2002 Published by Elsevier Science Ltd.