A problem of scaling in fracture of damaged rock

Pre-existing inhomogeneities such as micropores and microcracks dictate the mechanical and physical properties of rock. Overloading, weathering, changing temperatures, and exceptional events can increase this damage, usually by microcracking, and as a consequence, modify the effective properties of the rock. To examine the problem of a structure composed of rock with various stages of damage, three point bending tests on sandstone specimens exposed to elevated temperatures are presented, with a detailed evaluation of process-zone size. Both virgin rock, with pre-existing damage and heat-treated rock, with further damage, were tested by conducting experiments at ambient conditions after exposure to the high temperature. For virgin and heat-treated specimens, high resolution interferometric measurementswere used to characterize the evolution of the process zone as a function of the applied load. The size and shape of the localized damage zone due to increased microcracking are the significant factors influencing the strength and post-peak response of quasi-brittle materials. One of the aspects of this phenomenon is that structural scaling evolves with damage, which is explained by the increase of the process-zone size, and a decreasing influence of the scaling problem on nominal strength. As a result, a rigorous interpretation of the experimental data requires an identification of fracture parameters, and a convenient indirect method is proposed.