Sudden and violent fracturing of brittle materials, such as natural-forming rocks and artificial aggregates like concretes, still remain one of the leading causes of fatalities in mining, civil and geotechnical industries today. The primary aim of this research work is to investigate the mixed modes I (tensile) and II (shearing) fracturing mechanisms of Brisbane Tuff rock and prepared concrete samples using Semi-Circular Disc (SCD) and Cracked Chevron-Notched Brazilian Disk (CCNBD) specimen geometries. In order to create various mixed mode loading conditions, the chevron notch cracks of the CCNBD specimens were oriented at notch crack inclination angles, ß, of 0°:, 30°:, 45°:, and 70°: as part of the diametral testing procedure, whilst the SCB specimens were cut at the same ßs prior to conducting the three-point bending tests. The experimental study revealed that the CCNBD geometry and the Brisbane Tuff rock have higher failure loads than the SCD geometry and concrete sample counterparts. Following the experiments, a series of numerical analyses were then performed using FRANC2D software to simulate the stress distributions and fracturing behaviour of the samples at different ß values. Overall, this investigation showed ß, and hence the mixed mode loading condition, is a function of failure load, stress distributions, position of the pre-existing cracks relative to the major principal stress and fracturing behaviour of brittle materials
1. INTRODUCTION AND BACKGROUND
Engineering rock structures are primarily designed to withstand the loads they are expected to be subjected to whilst in service (Ceriolo and Di Tommaso, 1998). However, majority of mining, civil, and geotechnical large-scale structures are comprised of brittle materials (e.g. natural-forming rocks, construction aggregates, etc.) containing multiple inherent cracks and/or discontinuities that provide favourable paths for crack propagations (Chong and Kurrupu, 2012). Hence, when such rock mass structures are subjected to complex loading conditions, an abrupt and violent release of material’s stored elastic strain energy caused by rapid crack propagation is highly inevitable (Hoek, 1968). As a result, the mining, civil and geotechnical industries are persistently susceptible to significant safety hazards, material damage, and interruption or even cession of engineering operations (Szwedzicki, 2003).