Non-dissipative structural evolutions in granular materials within the small strain range

Microscale mechanisms involving the loss and gain of contacts in granular materials are non-dissipative in nature, but yet irreversible. This is because the creation or disintegration of contacts as an instantaneous event does not pertain to any global deformation of the granular system. Such a contact loss and gain regime is intriguing and has also been shown to play a significant role in altering the internal structure of granular materials, even at the relatively small strain range where irreversibilities can exist within deformation domains often attributed to elasticity. The current study offers a coherent decomposition of mechanisms affecting the microstructure of granular media, and subsequently investigates the contribution of non-dissipative/irreversible mechanisms to global structural rearrangement. An analytical scheme is put forward that relates the directional variations in contact losses and gains to the probability distributions of contact forces and interparticle separating distance, respectively. Thus, microstructural evolution can be statistically computed in terms of two key microvariables, i.e. coordination number and fabric anisotropy, and verified through 2D Discrete Element Method (DEM) simulations. The analytical scheme presented here provides an accurate description of microvariable evolution laws that are needed to formulate micromechanical constitutive models for granular materials.