Numerical study of stress distribution in sheared granular material in twodimensions

We simulate the response of dense granular material to shear. Our simulatio ns use a micromechanical model which includes realistic material models for each deformable grain, and a Coulomb friction model for interactions betwe en grains. We measure the probability density function (PDF) governing the volume distribution of stress for monodisperse and polydisperse samples, ci rcular and polygonal grains, and various values of microscopic friction coe fficients, yield stresses, and packing fractions. Remarkably, PDF's are sim ilar in form for all cases simulated, and similar to those observed in expe riments with granular materials under both compression and shear. Namely, t he simulations yield an exponential probability of large stresses above the mean. The relationship between distributions of boundary tractions and vol ume distributions of stress is discussed. The ratio of normal and tangentia l components of traction on the boundary defines a bulk frictional response , which is shown to increase with the intergranular friction coefficient. H owever, the bulk friction is always larger than the intergranular friction for densely packed samples. Bulk friction is also strongly dependent on gra in size distribution and shape. New observations of force-chain banding dur ing recrystallization, of slip systems in monodisperse samples, and of the effects of plastic yield, are also presented.