A viscoplastic constitutive equation bounded between two generalized plasticity models

The present work addresses a new rate-dependent inelastic constitutive equation, whose response Is always bounded between two distinct rate-independent generalized plasticity models. Main features of the proposed model are the following: (1) it approaches the two rate-independent generalized plasticity models for the case of fast and slow loading conditions, respectively; (2) it properly describes loading-unloading-reloading conditions for any loading rate; (3) it reproduces the experimentally observed difference between the dynamic and the static yielding conditions. These are all properties to be taken into account to obtain an accurate modeling for many different classes of materials, such as metals, polymers, geomaterials, shape-memory alloys. Both the time-continuous and the time-discrete version of the model are discussed. Moreover, a solution algorithmic within a return map setting as well as the form of the discrete consistent tangent tensor are addressed. Finally, some numerical simulations illustrate the performance of the proposed constitutive model.