Microcracks in rocks: a review

摘要: Abstract In the past decade number of studies about microcracks in rocks has rapidly increased. This review recent work concentrates on rock as separate entities, emphasizing microcrack morphogenesis, kinematics, dynamics, population statistics and observational techniques. Cracks are produced when local stress exceeds strength. The may be augmented by twin lamellae interactions, kink bands deformation lamellae, concentrations at grain boundary contacts around intracrystalline cavities. Local strength reduced along cleavage planes, boundaries any internal surface a result corrosion chemically active fluids. Dislocations appear not to significant factor for crack nucleation below 500°C silicates. Spatial temporal changes temperature can also induce microcracking differential thermal expansion between grains with different thermoelastic moduli conductivities. amount quartz effect thermally induced because its large variable expansivity. application hydrostatic pressure 100 200 MPa effectively closes most cracks, but closure uniform if wall asperities exist. Hydrostatic appears stabilize cracks make growth more difficult. average size mechanically is greater deformed higher pressures. deviatoric field mass results, microscopic scale, very complex system which greatly affects propagation paths. relative intragranular intergranular cracking depend upon mineralogy, type state. vast majority stress-induced extensional. Statistically, they predominantly oriented within 30° macroscopic maximum direction. Crack densities increase increases above threshold level. distributions either lognormal or exponential. Fracture under compressive loads coalescence many microcracks, single crack. Some configurations favorable than others. As failure approached, spatially from random locally intense zones cracking. Away fault, density dies off background level few away. Under lesser stresses, slow, subcritical occur stress-aided tip. rate governing mechanism chemical reaction water get Important details still remain worked out.