COMPUTER MODELING OF GRANULAR MATERIAL MICROFRACTURING

Microscopic observations indicate that intra- and transgranular fractu ring are ubiquitous processes in the damage of rock fabrics. Extensive modelling of intergranular fracturing has been carried out previously using the distinct-element approach. The current work is aimed at ext ending these results to include intra- and transgranular fracturing. N umerical experiments have been carried out to simulate these microfrac tures in granular media using a boundary-element computer code DIGS. G rains were represented by straight-sided polygons generated with a Vor onoi generator. Experiments were carried out to simulate experimental microfracture studies of quartzite in triaxial extension tests. The re sults support the experimental observations that the microcracks induc ed by compressive stress are extensile and sub-parallel to the directi on of maximum compressive stress. Various mechanisms of microcrack ini tiation were identified. Some cracks were found to be generated from i nside the grains in a manner similar to a Brazilian test. Sliding crac ks were found to start from grain boundaries as intergranular cracks a nd propagate as intragranular wing cracks in the direction of maximum compression. Pores were also modelled as a possible mechanism for micr ocrack initiation but were found to generate fractures in unexpected d irections relative to the direction of applied loading.