Numerical assessment of the rupture mechanisms in Brazilian test of brittle materials

The Brazilian test is probably the most widely accepted method for estimating the tensile strength of brittle materials due to its simplicity in sample preparation and ease of testing. However, despite its widespread use, various shortcomings have been noted since its introduction in the early 1940s. Overlooking these flaws has been shown to result in inaccuracies when determining the tensile strength of a given material. This study employs discrete element numerical simulations to explore some of these shortcomings in detail, with a particular interest in the loading platen curvature and stress distribution within the Brazilian disc and their impacts on the process of crack initiation and propagation. Micro-properties of the bonded particle model were first calibrated for a typical brittle material under different loading conditions. Loading platens with different jaw curvatures (disc-to-jaw curvature ratio in the range of 0 to 0.8) were simulated and the cracking mechanism inside the Brazilian disc was investigated. Results show that for curvature ratios less than 0.67, cracks are almost always generated in the vicinity of loading platens. When the curvature ratio approaches 0.8, tensile cracks initiate from the disc centre possibly due to the longer contact length available. A sensitivity analysis on the effect of disc and loading platen parameters was further conducted and it was found that particle and bond modulus, wall modulus, and particle & bond normal/shear stiffness are the key parameters controlling the transition of the crack initiation point from underneath of loading platens to the disc centre.