Interpretation of static and dynamic Young’s moduli and Poisson’s ratio of granular assemblies under shearing: Fid-Bau Portal

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

Li, Yang / Otsubo, Masahide / Kuwano, Reiko

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 ( $E_{sta}$ and $v_{sta}$ ) while stress wave measurements give dynamic values ( $E_{dyn}$ and $v_{dyn}$ ). 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 $E_{sta}$ and $E_{dyn}$ or $v_{sta}$ and $v_{dyn}$ 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 $E_{sta}$ and $E_{dyn}$ are equivalent during the entire axial range while $v_{sta}$ and $v_{dyn}$ are equivalent at initial elastic range. The stress-induced fabric anisotropy is found to have negligible effect on the comparisons between $E_{sta}$ and $E_{dyn}$ or $v_{sta}$ and $v_{dyn}$ 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 $E_{sta}$ measured from the small-amplitude cyclic loadings after creep is equivalent to $E_{dyn}$ at the pre-peak strain range.