A numerical study of the influence of heterogeneity on the strength characterization of rock under uniaxial tension

The behavior of a specimen under uniaxial tension and the process of micro-fracture in that specimen are phenomena of considerable interest in understanding the strength characterization of brittle or quasi-brittle materials such as rock. In this study, numerical results based on a Rock Failure Process Analysis code (RFPA(2D)) are presented. They show the nucleation and growth of macro-cracks in relatively homogeneous and heterogeneous specimens under uniaxial tension. Although the details of macro-crack formation vary from specimen to specimen, the numerical simulations consistently display a number of features. In relatively homogeneous specimens, the macro-crack nucleates abruptly at a point in the specimen soon after reaching the peak stress. Before macro-crack nucleation, acoustic emission (AE) events, or micro-fractures occur at locations that are randomly distributed throughout the specimen. It is very difficult to predict where the macro-crack will begin. The failed specimen has no residual strength. However, relatively heterogeneous specimens show a somewhat different response, with more randomly distributed AE events appearing in the early stage of loading. In contrast to the homogeneous specimens, macro-crack nucleation in heterogeneous specimens starts well before the peak stress is reached, and the crack propagation and coalescence can be traced, which can then be used to predict the macro-fracturing of the specimen. For specimens with the same heterogeneity, however, the numerical simulations show that the failure modes depend greatly on the crack initiation location, which is found to be sensitive to the local disorder features within the specimen. (C) 2006 Elsevier Ltd. All rights reserved.