ABSTRACT
Granular materials behave differently from usual solids or fluids and show peculiar mechanical properties like dilatancy, history dependence, ratcheting and anisotropy, see (de Gennes 1999) and references therein. The behavior of these materials is highly nonlinear and involves plasticity also for very small strain due to rearrangements of the elementary particles (Goddard 1990, Sibille 2009, Bardet 1994, Kumar 2014). The concept of an initial purely elastic regime (small strain) for granular assemblies is an issue still under debate in the mechanical and geotechnical communities (Einav 2012). Recent works (Ezaoui 2009, Zhao 2013, La Ragione 2012) show that along with the macroscopic properties (stress and volume fraction) also the structure, quantified by the fabric tensor (Luding 2005) plays a crucial role, as it characterizes, on average, the geometric arrangement of contacts. In particular, when the material is sheared, anisotropy in the contact network develops, as related to the opening and closing of contacts, restructuring, and the creation and destruction of force-chains. The anisotropic state is at the origin of interesting observations on wave propagation in sheared granular media.
