Noncoaxiality between Fabric and Stress in Two-Dimensional Granular Materials

This paper investigates the evolution of the fabric for different contact networks (i.e., the strong, weak, and overall contact networks) in granular material. Two-dimensional tests along proportional strain paths and simple shear tests are conducted using the discrete element method (DEM). Results show that the coaxiality between the principal directions of the fabric tensor for the overall contact network and that of the stress tensor depends on the loading conditions. The principal direction of the fabric tensor for the strong subnetwork is always coaxial with the stress direction. In addition, the major principal direction of the fabric tensor for the strong subnetwork is perpendicular to that of the weak subnetwork, regardless of any principal stress rotation. The fabric tensor for the strong subnetwork and the stress tensor at the critical state are proportional, with the coefficient of the proportionality being a function of the mean stress, if the critical stress can be approached.