A new methodology inspired from the Theory of Critical Distances for determination of inherent tensile strength and fracture toughness of rock materials

Measuring the intrinsic fracture properties of quasi-brittle materials like rocks is of great importance and at the same time a major issue for engineers. In this study, we explore the ability of the Theory of Critical Distances (TCD) to determine accurately both the tensile strength and fracture toughness. To this end, we conduct ring tests and semi-circular bend tests on four rock types including a red sandstone, a white coarse-grained marble, a finegrained granite and a coarse-grained granite. This selection covers sedimentary, metamorphic and igneous rock types with different grain sizes. The experimental data are analysed using a new methodology developed from the so-called Point Method (PM), a particular form of the TCD, from which we infer the intrinsic tensile strength and the fracture toughness of the studied rock materials. Our results are compared with those obtained from ISRM suggested methodology that is modified to take into account the finite notch root radius used in our experiments. The comparison is successful, supporting that the newly developed methodology is suitable to determine the intrinsic tensile strength and fracture toughness of rock materials.