ABSTRACT: The paper presents the results of a micromechanical study using the Discrete Element Method (DEM) to critically evaluate the determination of the tensile strength of brittle rocks using the Brazilian test. The Brazilian test is performed on model cylindrical specimens loaded with two diametrically positioned plates and fails by splitting the cylinder. In the study, a series of DEM models of the direct tensile and Brazilian tests was conducted in controlled conditions to establish the relationship between the bond strength between rock grains/particles and the tensile strength from the Brazilian test. The modeling was focused on size effects and micromechanical insights into the splitting and fracture propagation processes in the Brazilian test. The results of the micromechanical study lead to a scaling relationship to account for the effects of Brazilian test specimen size, and for practical recommendations to obtain more accurate estimations of the nominal tensile strength of the rocks from the Brazilian test data.
1. INTRODUCTION The Brazilian test is the most widely used method to obtain the tensile strength of brittle rocks in practice. For many engineering projects, such as deep rock fracturing, there is a need to obtain rock mechanical parameters with accuracy using economical and rapid test methods. However, the governing failure mechanism in a Brazilian specimen is not an instantaneous breakage caused by reaching the peak-cross-sectional nominal strength, or plasticity theory, like in the direct-tensile test, but instead is propagation of a fracture or crack until the cylinder splits. Hence, the Brazilian test results are subjected to the fracture-mechanics size effect [1]. In addition, experimental studies pointed out that loading rate, width of and friction between the contact between the sample and the loading plates have significant influence on the Brazilian tensile test results [2,3,4].