Computer modelling of granular material microfracturing

Abstract

Microscopic observations indicate that intra- and transgranular fracturing 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 extending these results to include intra- and transgranular fracturing. Numerical experiments have been carried out to simulate these micro fractures in granular media using a boundary-element computer code DIGS (Discontinuity Interaction and Growth Simulation). Grains were represented by straight-sided polygons generated with a Voronoi generator. Experiments were carried out to simulate experimental micro fracture studies of quartzite in triaxial extension tests. The results support the experimental observations that the micro cracks induced by compressive stress are extensile and sub-parallel to the direction of maximum compressive stress. Various mechanisms of micro crack initiation were identified. Some cracks were found to be generated from inside the grains in a manner similar to a Brazilian test. Sliding cracks were found to start from grain boundaries as intergranular cracks and propagate as intragranular wing cracks in the direction of maximum compression. Pores were also modelled as a possible mechanism for micro crack initiation but were found to generate fractures in unexpected directions relative to the direction of applied loading.