Fabric Evolution in Granular Materials Under Strain Probing

The fabric of granular materials, as the underlying internal contact network through which the interparticle forces transmit the stress, plays a key role in describing their elasticity, critical state, and dilatancy, to name a few. Just as response envelopes have been developed by Gudehus back in 1979 to get an overall picture of constitutive models and the nature of constitutive equations, herein, the evolution of contact fabric in granular materials when subjected to strain probes is explored through series of Discrete Element Method (DEM) simulations. As the first study of its kind, and also due to the richness of the observed responses, the scope of the study has been limited to isotropic configurations. The contribution of contact loss, gain, and reorientation mechanisms to the changes in the associated second order fabric tensor has been investigated as the proportion of vertical to horizontal strain changed during a strain probing procedure. Intriguingly, the evolution of fabric with strain probes shows a strong asymmetry in compression and extension, signalling an incrementally nonlinear relation between fabric and strain increments, despite the incrementally linear elastic stress-strain response. Such results suggest that the origins of the incrementally nonlinear stress-strain responses often observed in later stages of deviatoric loading of granular materials can be potentially traced back to characteristics of fabric evolution.