Experimental Study of Development of Fracture Process Zone in Rock

By means of digital image correlation (DIC) technology, the displacements and strains on the fracture ligaments of rock specimens were measured during loading. By analyzing the displacement distribution of each fracture ligament at different loading stages, the displacement fluctuation coefficient method was proposed to describe the development of fracture process zone (FPZ). The method can amplify the variation of displacement and clearly show the length of FPZ.The results show that: (1) the initiation of FPZ occurred at 77-89% of the peak load and the fluctuation coefficient of horizontal displacement around the crack tip reached the order of 10-7. (2) The initial length of FPZ was about 1.0-3.1 mm, which is 2 to 6 times the largest grain sizes. As the peak load was approached, the length of FPZ suddenly increased to 4.6-6.1 mm. (3) When a fracture process zone was initiated, the strain at the front end of the FPZ was about 3000-4000 mu epsilon. After the load approached the peak value, the strain at the rear end of the FPZ finally reached a peak value of 8000-11000 mu epsilon in all specimens.