Onset and impact of plastic deformation in granular compaction

The role of plastic deformation in the high-pressure compaction of granular material is investigated using bonded particle model simulations. Grains are discretized into a set of computational particles connected by pairwise bonds. Bonds are harmonic up to a plastic onset strain $\epsilon_p$ above which they yield, capping out at a maximum force and producing an elastic-perfectly-plastic-like mechanical response in grains. Packings containing over one thousand monodisperse spherical grains are isotropically compacted to different packing fractions to quantify how decreasing $\epsilon_p$ softens the rise in pressure and impacts effective elastic properties of the confined system. By isolating the relative decrease in pressure due to plasticity, we find data can be collapsed across a wide range of values of $\epsilon_p$ suggesting that relatively simple mathematical descriptions may capture plasticity's effect in granular compaction. Lastly, we study the microscopic statistics of local strains in grains and connect their evolution to the observed macroscopic behavior.