Micro-Macro Modeling Approach for the Triggering of Viscous Fatigue Damage in Halite Polycrystals under Cyclic Loading

Abstract

Underground cavities in salt rock formations used for Compressed Air Energy Storage (CAES) undergo cyclic loads and are subject to a fatigue phenomenon that induces a decrease of rock’s strength and stiffness. A micromechanical analysis of this phenomenon is necessary to understand its mechanisms and elaborate relevant constitutive models. The polycrystalline nature of rock salt has a crucial effect on crack propagation and rock damage and, hence, on fatigue behavior. This behavior was investigated herein on the basis of self consistent upscaling approaches for viscous heterogeneous materials. The internal stresses in the polycrystal were modeled based on experimental data available for halite single crystals, and a monotonic compression test was simulated, which allowed tracking the triggering of fatigue damage. Results show that tensile stresses are developed in the polycrystal under global compressive load, the amplitude of which depends on the macroscopic load rate or frequency. These tensile stresses can exceed in some conditions the tensile strength of grains or of grains interfaces and cause cracking and damage in the polycrystal.