Microscopi observation and contact stress analysis of granite under compression

To study the damage process of microscale to macroscale in coarse-grained granite specimen under uniaxial compressive stress, we have observed micro-damage localization and propagation by using a newly developed experimental system that allows us to observe the damaging process continuously. The results showed that pre-existing microcracks lead to macroscopic shear fracture through the damage development process. The mechanism of micro-damage initiation in a granite specimen under uniaxial compressive stress may be considered for two cases. One is that two grains such as quartz and feldspar contact each other in the same direction as the axial stress, and the other is that a biotite grain inclined to the axial stress direction is surrounded by feldspar grains. The homogenization theory was applied to verify numerically the micromechanics of stress-induced damage in the mineral contacts. Local stress distribution in the periodic-micro structure was also calculated by the homogenization theory. It is shown that this analysis, which takes into account the initial state of the specimen, is well adapted to the behavior of two grains for which microcracking is the fundamental mechanism of damage.