The assessment of fracture properties such as crack tip opening displacement (CTOD), plastic zone size, and crack development is essential for understanding the behavior of cracks and fractures in geological materials. Crack displacement requires full-field strain measurement as the strain field develops in front of the propagating crack. The point-based strain measurement devices, such as strain gauge and extensometers, fails to capture crack growth. This study proposes a Finite Element based Digital Image Correlation (FE-DIC) method for measuring fracturing process especially, crack tip displacement and associated strain localization. The paper outlines the FE-DIC algorithm and its validation with numerical images and laboratory testing. The numerical images are created using Irwin's near-crack tip displacement approximation function around a center crack in an infinite plate under equibixial tension (Irwin, 1957). In the laboratory, the Mode I three-point bending fracture test is performed on a cuboidal slab of sandstone and basalt rock with a center notch. The results show that the FE-DIC method can capture the non-linear displacement field as the crack propagates and also estimate plastic zone around the crack. The findings of this study provide evidence supporting the efficacy of the global FE-DIC method in visualizing strains and fracture propagation.
The study of the rock fracturing process is crucial for designing various geotechnical projects such as mines, dams, reservoir, underground nuclear waste disposal, and tunnels (Guo et al., 2023; Xing et al., 2022). Most rocks exhibit strain-softening to brittle behavior and fail without any prior indication. To understand the failure mechanism of rocks due to fracture propagation, the insight of full field deformation under various loading conditions is a necessity. Critical challenges in characterizing the crack-induced rock failure includes locating the crack, estimating its propagation path and identifying the strain localization zone in the crack tip where the stress-strain relationship is non-linear, which acts as the precursor of the macroscopic crack extension known as Fracture Process Zone (FPZ) (Qiao et al., 2023). These challenges are more prominent while dealing with brittle materials like rock, which fails at low strain and thus demands a robust fullfield deformation measurement method.
