Application of digital image correlation method in experimental research on crack propagation of brittle rock

Under uniaxial compression, wing crack initiates and propagates in the flawed rock, and the damage evolves. The uniaxial compression tests are carried out on rock-like brittle specimens, each containing a single flaw. Two high-resolution camera are used to capture images to get the global strain fields of the specimens using digital image correlation (DIC) technology. Micro-crack zone is observed obviously at the flaw tip, whose shape is an ellipse with an inclination of 82° with flaw. When the load increases to 85.6% of the maximum load, the micro-crack nucleates, and the macro wing crack initiates at the flaw tip. The cracking propagation is a process of micro-crack development and nucleation, as well as a process of high-strain area spreading. The development of the secondary micro-crack zone and the anti-wing micro-crack zone is very slow. Meanwhile, they are affected by the tensile stress. Therefore, the wing crack is the main crack pattern. Furthermore, the change of stress and strain around the tip is compared based on LEFM. It proves more effective to use the strain approach to investigate crack initiation and propagation. And the reliability of DIC system is verified through theoretical analysis.