Directional modeling concept for large strain metal plasticity

Abstract

This paper improves a modeling tool called “concept of representative directions”. Employing this approach, experienced and novice users can construct advanced nonlinear models of inelastic material behavior in a straightforward way. Unfortunately, the classical version of this concept lacks w-invariance, which effectively prevents the applicability to finite strain metal plasticity. To overcome this limitation, we introduce two enhanced versions of the concept that ensure w-invariance. The resulting material models are objective, with one approach also being thermodynamically consistent. These advancements are not purely theoretical: numerical tests demonstrate that the new formulations significantly improve the accuracy of modeling actual material behavior in the finite strain range. While the classical concept induces parasitic hardening, our advanced w-invariant models eliminate this inconsistency. Furthermore, the new approach has been implemented in the commercial FEM code MSC.MARC, and its practical utility is showcased through an initial boundary value problem. The generalizations to other material nonlinearities like metal creep and ratcheting are straightforward.