IMPROVEMENT OF BRAZILIAN TEST:FROM FLATTENED BRAZILIAN DISC TO GROOVED BRAZILIAN DISC

Brazilian test, a standard method for measuring the tensile strength of concrete, ceramics, rock, and other brittle or quasi-brittle materials, has been widely applied in materials science and civil engineering, research on its improvement attracted ever-growing attention in scientific and engineering communities. We ideate a new specimen configuration to improve the Brazilian test, i.e. grooved Brazilian disc (GBD), with a pair of narrow and shallow groove produced at opposite ends of the loading diameter, GBD relieves the shortcoming of non-central crack initiation possibly inherent to the original complete Brazilian disc (BD) under diametrically compression, having the same merit pertaining to our previously-proposed flattened Brazilian disc (FBD). GBD is also more general in specimen configuration, as it represents both BD and FBD. More advantages may be obtained if the geometric parameters of GBD are suitably chosen by referring to the analytical stress formulas, derived by superposition of two models we proposed for solving the compressive stress and tensile stress respectively. The derived two simple stress formulas can be used to predict qualitatively the stress evolution trend, both at and near the front of the apex of the groove, and also the influencing geometric parameters of GBD, which are also confirmed by quantitative numerical calculations with finite element method. The analytical formulas, numerics and comparative experimental result jointly indicate:a slight change in the geometry and surface boundary condition of a disc-type specimen under diametral compression turns around a substantially favorable change for the stability and fracture process of the specimen, making the GBD more favourable in the Brazilian test.