Fracture coalescence has been identified as one of the factors playing an important role in the behavior of brittle materials. In this paper this phenomena is simulated by using an in-house implementation of the Combined Finite-Discrete Element method (FDEM). Key aspects of FDEM include the introduction of finite displacements, finite rotations, and finite strain based deformability combined with suitable material laws; the incorporation of discrete element based transient dynamics, contact detection, and contact interaction solutions and objective discrete crack initiation and crack propagation solutions that have a great deal of fidelity in reproducing complex fracture patterns and eventual fragmentation. The first examples presented in this paper consist of compression virtual experiments conducted on specimens that have two pre-existing flaws inside them. These fractures are arranged through the thickness of the specimens following different geometrical layouts. Some of the main features of the fracture propagation processes reported in this work are: initiation of wing cracks and secondary cracks; direction and propagation of the newly generated cracks and patterns of fracture coalescence. The results obtained in the simulations are qualitatively compared with experimental observations reported in the literature. This work is then extended to present results for a larger scale problem wherein fracture coalescence networks are observed when a pre-existing in-situ fracture network is stimulated.
Rock contains a large number of natural fractures at various scales as the result of a variety of geological processes. A thorough understanding of the cracking initiation, propagation, interaction and eventual coalescence processes emanating from existing in-situ flaws can benefit geological engineering design and implementation . In order to understand the fracture process within brittle solids, Horii and Nemat-Nasser carried out a series of uniaxial compression tests using resin plates that contained artificial pre-existing cracks . Following their work, crack coalescence in rock materials has been extensively studied, both experimentally and numerically [3-9].