Experimental Study on Loading Rate Effects on the Tensile Strength and Fracture Toughness of Rocks

The Brazilian method experiments were applied to investigate effects of loading rate on tensile strength of gabbro-diorite, marble, granite. The tensile strength was measured over a wide range of loading rate, \(\dot{\sigma } = 10^{ - 3} - 10^{2}\) MPa s. Also the fracture toughness of marble, gabbro-diorite, dolerite were measured over a wide range of loading rate from 5 × 10⁻⁴ to 25 MPa m^1/2/s by three-point bending of beams with a central narrow cut. The strength and fracture toughness of studied rocks are related to the loading rate by typical equations: \(\sigma = a + e\ln \dot{\sigma }\) and \({\mathcal{K}}_{1c} = c + d\ln \dot{K}_{1}\) in the range of loading rates of 10⁻³–10² MPa/s. A comparison of the characteristic fracture parameters for both types of tests showed the initial activation energy of fracture has the same values. The parameters of proportionality were compared on the basis of the integral strength criterion. The obtained parameters of the studied rocks allow extrapolating the results of measurements of strength and fracture toughness for longer periods, it is important for estimating the long-term stability of rock structures. The methodology for determining the characteristics of rock fracture from the loading rate in static fracture of rocks can be easily applied to other brittle materials.