Abstract: An Oriented-Element Theory (OET) originating with one of the present authors, Liang , is developed for studying viscoplastic behaviors of polycrystalline metals subjected to complex loading paths. Application of the work-conjugate principle and the field-average method leads to a concept of “oriented-element”, i.e. a representative or an averaged slip system for those practical slip systems that have the same orientations, from which a concise viscoplastic constitutive equation is derived. A numbe...