Non-Local Micromechanical Anisotropic Damage Modeling Of Quasi-Brittle Materials: Formulation And Implementation
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A nonlocal anisotropic damage model is proposed for quasi-brittle materials, such as concrete and rock. The local anisotropic damage model is formulated by combining a free energy derived from micromechanics with phenomenological yield criteria and damage potentials. The trace of the total strain is used to distinguish tensile and compressive loading paths, and to account for the influence of the confining pressure on the propagation of compression cracks. Yield criteria in tension and compression are expressed in terms of equivalent strains, which depend on the difference between principal strain components. A non-local measure of strain is used to avoid localization. Constitutive parameters are calibrated against published experimental data for concrete and shale. Simulations of three-point bending tests show that non-local enhancement is necessary and efficient to avoid mesh dependency upon strain softening. Simulations of borehole excavation damage zone show that the damage model is not mesh dependent upon stress hardening. Numerical predictions are in agreement with experimental observations and the model can capture unilateral effects, tensile softening, compressive hardening and confinement dependent compressive behavior.