An enhanced tool for probing the microscopic behavior of granular materials based on X-ray micro-CT and FDEM

We propose an enhanced tool by combining X-ray micro-computed tomography test and hybrid finite and discrete element method to investigate the mechanical behaviors of granular materials. We first conduct a min-triaxial test of Ottawa sand under X-ray micro-CT. Then, spherical harmonic analysis is performed to characterize multi-scale morphological characteristics of particles and used in the particle matching. The particle tracking algorithm ensures the matching accuracy between particle configurations even at large strain intervals. To probe intra-particle contact force, we reconstruct the numerical sample from X-ray image data. Without calibrating material parameters, FDEM simulation quantitatively agrees with the overall response of Ottawa sand recorded in experiment. Moreover, the particle scale dynamics obtained by simulation are remarkably quantitatively consistent with experiment results. The proposed tool sheds new light on bridging length scales from particle to granular system. We find that the granular material deforms plastically through spatially localized zones of large nonaffine displacements, and the spatiotemporal evolution of these zones controls the macroscopic responses of the system. The force chain collapse is relevant to the large induced structural voids formation within the shear transformation zones. Furthermore, we discover a connection between particle stress fluctuations and particle plastic rearrangements in granular materials.