Stiffness and Deformation of Rock Subjected to Anisotropic Damage and Temperature-Dependent Healing
Chester, Fred M.
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This research is motivated by the increasing need for geostorage facilities, mainly: nuclear waste disposals, high-pressure gas reservoirs and carbon dioxide sequestration systems. A new constitutive model is formulated to account for anisotropic damage due to tensile cracks and healing due to Diffusive Mass Transfer (DMT). The damage variable is the difference between the second-order crack density tensor and a scalar viscoplastic healing variable. The viscoplastic healing variable is needed to model the effects of DMT on the reduction of damage-induced deformation. Contrary to the damage and healing models proposed previously for salt rock, the proposed framework accounts for crack-induced anisotropy, and anisotropy is treated in both damage and healing evolution laws. Compression, extension and compression loading and unloading cycles have been simulated with Theta-Stock Finite Element code. The results illustrate well the influence of anisotropic damage on stiffness degradation and residual strain development. An algorithm has also been written to study the trends of the coupled damage and healing model for a stress path comprising an isotropic compression, and axial compression, a healing period and an unloading phase. The results match the theoretical expectations, and show that the proposed model can predict anisotropic damage and healing.