Sliding and rolling dissipation in Cosserat plasticity

Based on micromechanical considerations at the level of grain contacts and taking into account the way in which kinematic and static quantities are introduced at grain surface and grain centre, we identify appropriate measures related to energy dissipation due to rolling and sliding between grains, within both a discrete and a Cosserat continuum description. This allows us, within the framework of Cosserat plasticity, to identify appropriate invariants and formulate simple forms of the respective yield surfaces. The resulting model is shown to be a multiple-yield-surface generalisation of the model by Mühlhaus and Vardoulakis (Géotechnique 37(3):271-283, 1987). By introducing separate and clearly identified rolling- and sliding-resistance parameters, the model allows for separate activation of the respective dissipative mechanisms. © 2011 Springer-Verlag.