Noncoaxiality and force chain evolution

Classical plasticity is predicated on the coaxiality between the principal directions of stress and plastic strain rate. However, there is now extensive evidence which show that these directions are necessarily noncoaxial for cohesionless granular systems. We investigate the micromechanical origins of noncoaxiality in specimens undergoing strain localization, from the standpoint of force chain evolution and associated kinematics. Connections to macroscopic trends in simple shear and biaxial tests are discussed.