Analysis of internal state and strains in granular material at meso-scale: influence of particle shape

Abstract

Using Non Smooth Contact Dynamic formalism to conduct contact dynamics simulations, we investigate the internal state and deformation of two granular numerical materials composed of poly-sized circular and polygonal rigid particles. The 2D granular specimens are subjected to classical biaxial loading. The main goal of this study is to generalize the results previously obtained for assemblies of disks (Nguyen et al. in Int J Solids Struct 46:3257–3271, 2009). Since the spherical geometry of this type of grain leads to overestimating the role of rotations and facilitates deformation, we want to evaluate incremental response by using circular and angular particles Furthermore, as rigid contacts are modeled, the simulations considered allow accurate information on irreversible strains to be obtained. These samples are analyzed at a meso scale composed of closed loops of particles in contact. The texture at the meso level is characterized by parameters such as local density and the shape and orientation of the meso domains. Six types of meso domain, called six phases, are defined to perform a thorough analysis at this level. It is shown that throughout compression tests the phases composed of meso domains oriented in the compression direction increase, leading to greater anisotropy in the direction of compression. All these evolutions were more marked for the material containing polygonal particles. Based on an analysis proposed in a previous paper (Cambou et al. in Euro J Mech A Solids 19:999–1014, 2000), the incremental strain at meso scale is defined, whatever the particle shapes. The local strain tensor in the six phases is analyzed throughout the loading. The phases of meso domains oriented in the compression direction present more rigid behavior and greater dilatancy.