Numerical investigations of shear strain localization in an elasto-plastic Cosserat material

The phenomenon of strain localization in narrow zones, called shear bands, is mainly related to the micro-structure of granular materials. This phenomenon cannot be modeled properly within the framework of classical continuum especially in the post bifurcation regime due to the lack of characteristic length of the micro-structure. For finite element calculations, Cosserat (micro polar) continuum is an effective regularization technique to remove the numerical difficulties when shear localization occurs. The paper presents numerical investigations of shear strain localization in plane shearing of an infinite granular layer as well as biaxial compression of a specimen using micro-polar (Cosserat) continuum approach. It is shown that the micro-polar effects i.e., Cosserat rotations, micro-curvatures and couple stresses are significant in the emerged shear bands. Shear banding pattern is significantly affected by the prescribed micro-polar boundary conditions of entire system as well as geometry of specimen. It is confirmed that the proposed elasto-plastic Cosserat model is capable to predict the evolution of micro-polar effects within the shear band.