Microcrack modelling of Brazilian tensile tests with the boundary element method

This study focuses on the influence of initiated cracks on the stress distribution within rock samples subjected to indirect tensile loading by traditional Brazilian testing. The numerical analyses show that the stress distribution inside the models is only marginally affected by the friction between the loading platens and the sample. On the other hand, the initiation and propagation of cracks produce a stress field that is very different from that assumed by considering the rock material as continuous, homogeneous, isotropic and elastic. In the models, stress concentrations at the bridges between the cracks were found to reach tensile stresses much higher than the direct tensile strength of the intact rock input in the numerical models. This was due to the development of large stress gradients between the cracks. The analysis of the deformation along the sample diameter perpendicular to the loading direction might enable one to determine the direct tensile strength of the rock. In fact, when the tensile strength is reached, initiation of cracks in the sample induces a sudden increase of the rate of the diametric strains. The direct tensile strength is therefore indicated by the point where the stress–strain curves in the direction perpendicular to the loading diameter depart from linearity.