EXPERIMENTAL-STUDY OF FRACTURE PROCESSES IN ROCK

The Fracture process zone in compact tension specimens of Indiana limestone was investigated to study its effect on the fracture mechanics parameters in such materials. Specimens were tested up to the peak load, and propagation of the crack from a preexisting notch was monitored. Experiments were designed to study the two features of the fracture process zone in rocks: ligament connections and microcracking. To observe this zone with high sensitivity and accuracy, laser interferometry methods were adopted. Holographic Interferometry was used to observe initial crack propagation. To obtain more quantitative measurements of the displacement field, in realtime, the recently developed technique of electronic speckle pattern interferometry was applied. This technique can provide continuous video recording of the interferometric fringe pattern, depict the evolution of the fracture process, and measure profiles of crack opening displacements. The macroscopic observations of full-field displacement by the laser techniques were supplemented by post mortem observation of the fractured region under a scanning electron microscope. Regions around the crack were studied after the test for possible presence of microcracks. An interactive finite element code was used to compute the stress intensity factors of the propagating crack-tip and displacements. Finite element computations were used to evaluate the effect of the process zone on crack propagation.