A study of non-coaxial effects on strain localization via micropolar plasticity model.

The conventional flow rule and plasticity constitutive models implicitly assume that the principal stress and plastic strain rate are coaxial, which often result in various setbacks in modeling, for example, the bifurcation and the evolution of shear band cannot be accurately and adequately captured. In this work, we investigate the non-coaxial effects of an elastoplastic constitutive model on strain localization in the framework of micropolar plasticity theory. The vertex-like yield surface is introduced in the flow rule, and a non-coaxial Drucker–Prager model is implemented in a user-defined finite element subroutine (UEL) in ABAQUS. The simple shear test and the plane strain compression test have been conducted to study the non-coaxial stress–strain response and the strain localization behavior. Effects of boundary condition on bifurcation, shear band orientation and thickness are investigated. Results indicate that the proposed model shows a good performance in the simulation of the non-coaxial behavior of geomaterials. On the premise of overcoming mesh dependency, the shear band orientation and width predicted by the non-coaxial model possess higher values than those predicted by the coaxial model, and a better agreement with the experimental results are achieved by the non-coaxial model. Moreover, by analyzing stress–strain responses, we have found that material strength may be systematically overestimated by the coaxial model. [ABSTRACT FROM AUTHOR]