Numerical modeling of dynamic rock fracture with a combined 3D continuum viscodamage-embedded discontinuity model
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This paper deals with numerical modeling of dynamic failure phenomena in rate-sensitive quasi-brittle materials, such as rocks, with initial microcrack populations. To this end, a continuum viscodamage-embedded discontinuity model is developed and tested in full 3D setting. The model describes the pre-peak nonlinear and rate-sensitive hardening response of the material behavior, representing the fracture-process zone creation, by a rate-dependent continuum damage model. The post-peak response, involving the macrocrack creation accompanied by exponential softening, is formulated by using an embedded displacement discontinuity model. The finite element implementation of this model relies upon the linear tetrahedral element, which seems appropriate for explicit dynamic analyses involving stress wave propagation. The problems of crack locking and spreading typical of embedded discontinuity models are addressed in this paper. A combination of two remedies, the inclusion of viscosity in the spirit of Wang's viscoplastic consistency approach and introduction of isotropic damaging into the embedded discontinuity model, is shown to be effective in the present explicit dynamics setting. The model performance is illustrated by several numerical simulations. In particular, the dynamic Brazilian disc test and the Kalthoff-Winkler experiment show that the present model provides realistic predictions with the correct failure modes and rate-dependent tensile strengths of rock at different loading rates. The ability of initial embedded discontinuity populations to model the initial microcrack populations in rocks is also successfully tested.