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Volume-Averaged Stress States for Idealized Granular Materials using Un­bonded Discrete Spheres in LS-DYNA

The discrete element method (DEM) permits study of the kinetics of microscopic particles through use of the kinematics of contact mechanics, and has been used by numerous researchers to investigate kinematically admissible deformation fields observed in laboratory tests of Representative Elementary Volumes (REV) of granular masses. In the current study, newly-implemented discrete element analysis features within LS-DYNA are used to simulate three-dimensional (3D) quasi-static stress states for idealized bodies of granules subjected to quasi-static loading conditions. Operating within a 3D Cartesian domain, volume-averages of summed dyadic products of contact forces and branch vectors (obtained from LS-DYNA simulation results) are used to investigate stresses that develop across various regions of uniform, unbonded discrete element sphere (UDES) assemblies, where the contact forces arise due to body forces that are prescribed at the centroid of each sphere. When feasible, averaged local force results (micromechanical stresses) obtained from LS-DYNA simulations are compared to corresponding manual calculations. As demonstration of the LS-DYNA DEM capabilities, and as a means of showcasing a recently implemented stress computation algorithm specific to the use of UDES, volume-averaged stress quantities are investigated at three scales: 1) On an individual sphere within a two-dimensional simple, pyramidal assembly; 2) On an REV associated with laboratory-scale triaxial compression testing; and, 3) On multiple REVs sampled from a megascopic assembly. The as-demonstrated discrete element analysis of the particulate equations of motion can be applied to modeling of in-situ granular soil conditions, where geostati