Incremental response of a model granular material by stress probing with DEM simulations
Résumé
We use DEM simulations on a simple 2D model of a granular material to test for the applicability of elastoplasticity (yield criterion, flow rule) to the response to stress increments of arbitrary directions. We apply stress probles in a three-dimensional stress space to various intermediate states (investigation points) along the biaxial compression path, and pay special attention to the influence of the magnitude of the increments The elastic part of the material response is systematically identified by building the elastic stiffness matrix of well-equilibrated configurations. The influences of the contact stiffness level and of the dominant strain mechanism, contact deformation (I) or network rearrangement (II), are considered. Stress increments sharing the same principal directions as the stress state in the ubvestigation point comply with a standard (single-mechanism) elastoplastic model with a Mohr-Coulomb criterion and well-defined flow rules and plastic moduli. Stress increments with principal axis rotation entail a response which is satifactorily modeled by superimposing 3 plastic mechanisms, 2 of them symmetrically corresponding to shear stresses of both signs. The full dependence of strain increments on sterss increments is thus parametrized with three flow rules, two of which are essentially symmetric.
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