Using Microstructure Descriptors to Model Thermo-mechanical Damage and Healing in Salt Rock
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Creep processes in halite (salt rock) include glide, cross-slip, diffusion and dynamic recrystallization. Diffusive Mass Transfer (DMT) can result in crack rebonding, and mechanical stiffness recovery. On the one hand, viscoplastic laws relating creep microscopic processes to microstructure changes are empirical. On the other hand, theoretical models of damage and healing disconnect thermodynamic variables from their physical meaning. The proposed model enriches the framework of Continuum Damage Mechanics (CDM) with fabric descriptors. In order to infer the form of fabric tensors from microstructure observation, creep tests were carried out on granular salt under constant stress and humidity conditions. A stress path comprising a tensile loading, a compressive unloading, a creep-healing stage and a reloading was simulated. Macroscopic and microscopic model predictions highlight the increased efficiency of healing with time. A preliminary Finite Element model illustrates the impact of healing on the stress distribution in the Excavation Damage Zone (EDZ). The model presented in this paper is expected to improve the fundamental understanding of damage and healing in rocks at both macroscopic and microscopic levels, and the long-term assessment of geological storage facilities.