Evaluation of Microstructural Critical Level of Damage Using Percolation Theory in Barre Granite During Brittle Creep

ABSTRACT: Brittle rocks consist of a system of mineral grains, pores, and pre-existing flaws/cracks. Under a given loading condition, system-scale instability does not develop until the formation and growth of cracks within the system reach a critical density and configuration known as the microstructural critical level of damage. Many scholars have attempted to characterize microstructural critical level of damage prior to failure in rocks during brittle creep. While macroscopic proxies have been widely used for evaluation of microstructural critical damage level at the onset of accelerating (tertiary), these proxies fail to capture the small-scale (i.e. millimeter and smaller) fracturing process and connectivity of damage. In this study, we present brittle creep testing results for Barre granite (BG) subjected to different levels of constant stresses to evaluate and quantify the microstructural critical level of damage. To perform our analysis, we utilize two-dimensional digital image correlation (2D-DIC) to characterize the microstructural critical level of damage using percolation theory, which evaluates the connectedness of elements within the system, during brittle creep experiments. The site percolation parameter is evaluated at the transition to accelerating creep and the failure points of all test specimens. The study reveals that percolation theory consistently quantifies the microstructural critical damage level in BG specimens regardless of applied constant stress and time to failure.