Résumé
How particle shape affects the complex rheology of granular materials is a vast topic which is now being increasingly addressed both experimentally and numerically. However, a systematic and quantitative investigation of shape-dependence is still largely elusive since particle shape character- istics such as elongation, angularity, slenderness and nonconvexity are described by distinct groups of parameters, and the effect of each parameter is not easy to isolate experimentally. In this work, we introduce a low-order parameter n which describes the degree of distortion from a perfectly circular/spherical shape in 2D/3D. We shows that, for several simulated packings composed of different particle shapes (Fig. 1), the shear strength is an increasing function of n whereas the solid fraction increases first to a maximum value but declines as n increases. Another interesting finding is that the effect of specific shape parameters (angularity, nonconvexity, elonga- tion,...) is of second order. Performing an additive decomposition of the stress tensor based on a harmonic approximation of the angular dependence of contact normals and forces, we show that the increasing mobilization of friction force and the associated anisotropy are key effects of particle shape.