Interpretation of static and dynamic Young’s moduli and Poisson’s ratio of granular assemblies under shearing

Abstract

Young’s modulus (E) and Poisson’s ratio (v) of granular assemblies are two essential mechanical properties. Measurements based on stress–strain relationships gives static values (Esta and vsta) while stress wave measurements give dynamic values (Edyn and vdyn). This study adopts the discrete element method (DEM) to investigate the evolution of E and v regarding various loading probes under drained conditions at selected strain levels from the original loading. The DEM results reveal that Esta and Edyn or vsta and vdyn are not always equivalent for face-centred cubic (FCC) packings and random/disordered packings (RDP). When samples are beyond the initial elastic range, either increasing friction coefficient or conducting unloading leads to a recovery of elasticity where Esta and Edyn are equivalent during the entire axial range while vsta and vdyn are equivalent at initial elastic range. The stress-induced fabric anisotropy is found to have negligible effect on the comparisons between Esta and Edyn or vsta and vdyn under various loading probes. Microscopic investigations signify that mean contact force ratio and fraction of slip contacts are key parameters to evaluate elasticity. Besides, the supplementary laboratory tests are conducted using spherical glass beads in which Esta measured from the small-amplitude cyclic loadings after creep is equivalent to Edyn at the pre-peak strain range.