Deformation mechanisms in granular flows

Abstract

Understanding the evolution of deformation fields in sheared granular flows is essential to elucidate their complex flow behaviours. This thesis investigates the mechanisms driving local deformation in dense granular flows, utilising discrete element simulations in plane shear configurations. The research focusses on the spatiotemporal evolution of kinematic fields and their relation to the constitutive laws that govern granular flows at the continuum scale. It reveals that the particle rearrangements within these flows are neither spatially uniform nor temporally steady, particularly at lower inertial numbers. The findings demonstrate a diffusive propagation mechanism for shear deformation, where local particle rearrangements trigger further rearrangements nearby, creating zones of increased deformation. This mechanism suggests a connection between distant regions of the flow, propagating across a mesoscopic distance that varies with the inertial number. These insights provide a potential microscopic basis for non-local behaviour observed in continuum-scale models. Key findings include the characterisation of length scales and Representative Volume Elements (REVs) associated with kinematic heterogeneities, such as velocity fluctuations, deformation, and nonaffine deformation, and the identification of the role of kinematic clusters in these processes. The results of this thesis contribute to bridging the gap between continuum and discrete descriptions of granular flows by elucidating the microstructural processes underlying their rheological behaviours. The findings emphasise the importance of incorporating large-scale structures and micromechanics of deformation into the development of more accurate continuum models.