The effect of particle elongations on incremental behavior of granular materials using discrete element method

Abstract

This study offers a novel investigation into the incremental behavior of granular materials by focusing on the effects of particle elongation on mechanical properties and microstructural evolution. Through a series of Discrete Element Method (DEM) simulations, samples with varying elongation coefficients ($\eta$) are systematically analyzed using two strain decomposition methods: the energy dissipation constraint method and the loading cycle method. The results show that as $\eta$ increases, the strain envelope size decreases, indicating greater stiffness. A ‘memory effect’ is observed in the elastic strain envelope, suggesting internal rearrangement and partial microstructural recovery in later stages. The plastic strain envelope exhibits distinct patterns that vary with loading conditions, with magnitude decreasing as $\eta$ increases. Despite identical initial stress states, the orientation of the plastic strain envelope shifts significantly, highlighting the impact of loading history and anisotropy. Notably, the misalignment between the normal direction of the yield surface and the incremental plastic flow direction indicates a non-associated flow rule for the generated granular materials. This misalignment varies with $\eta$ and loading conditions. The study also reveals a transition from contraction to dilation behavior across different probing states, with increasing $\eta$ leading to a denser packing of particles with a lower void ratio. As $\eta$ increases, the anisotropy within the granular assembly becomes more pronounced, leading to a stronger directional dependence of the mechanical response.