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

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TECHNICAL NOTE

Experimental Study on Loading Rate Effects on the Tensile Strength and Fracture Toughness of Rocks Viktor P. Efimov

Received: 20 March 2020 / Accepted: 11 July 2020 Ó Springer Nature Switzerland AG 2020

Abstract 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, r_ ¼ 103  102 MPa s. Also the fracture toughness of marble, gabbro-diorite, dolerite were measured over a wide range of loading rate from 5 9 10-4 to 25 MPa m1/2/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: r ¼ a þ e ln r_ and K1c ¼ c þ d ln 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.

V. P. Efimov (&) Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Krasnyi pr. 54, Novosibirsk 630091, Russia e-mail: [email protected]

Keywords Strength  Fracture toughness  Rock  Loading rate  Fracture activation energy  Lifetime

1 Introduction The brittle fracture of many products and construction often seems an unforeseen phenomenon. It is explained by the fact that the process of final fracture is due to the rapid propagation of cracks which happens faster comparing with the durability of the construction. The investigation of the phenomenon of fracture as process evaluating during time is very important for forecasting and estimating of the resource of a construction. Since the time of tests or experiments is limited, while the resource of many constructions must far exceed duration of such tests, it is important to extrapolate the test results for longer periods. It is especially important to study the longterm strength of rocks, since the actual service period of mining objects exceeds any achievable experiment time. Although many building materials and rocks work in compression, knowing the value of the tensile strength is extremely important. A simple calculation shows account the internal structure of the medium and the presence of boundaries leads to the appearance of areas in the specimen that experience tension under unequal compression. In fact, material is fractured by

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tensile tension under compressive stresses at the mac

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