Fabric response to stress probing in granular materials: Two-dimensional, anisotropic systems

The microstructure of granular materials has a significant influence on their macroscopic quasi-static strength and deformational behaviour. This microstructure is often quantified by a second-order fabric tensor that describes the primary orientational statistics of interparticle contacts. Here, it is investigated how the fabric tensor changes when samples are subjected to small (strain) loadings with different ‘directions’, i.e. probes. This is accomplished by the analysis of extensive sets of Discrete Element Method (DEM) simulations for various anisotropic, pre-peak two-dimensional samples, where both in-plane (i.e. coaxial with the current stress and fabric tensor) and out-of-plane, noncoaxial probes are considered. The results of DEM simulations show that the in-plane and out-of-plane fabric responses are effectively decoupled, i.e. they are only dependent on the in-plane and out-of-plane strain increment, respectively. The out-of-plane fabric increment is proportional to the out-of-plane strain increment whereas the in-plane fabric increment is linearly dependent on the in-plane strain increment. An accurate theoretical description (with a modest number of model parameters) has been developed that describes the fabric response to the imposed, in-plane as well out-of-plane, strain increments for the considered systems.