New rock II-type fracture toughness test method

Abstract

The invention relates to a new rock II-type fracture toughness test method. According to the invention, on the basis of an original shear box test, by means of adjustments of the stress state of a loaded mould and arrangement of a sample to eliminate rotation tendency of the sample, generation of an excessive tensile stress on a crack tip is inhibited, thereby achieving rock II-type fracture toughness test. A test model includes a square rock sample and two steel loading moulds. Straight cracks are pre-formed on the middle parts of the two sides of the square rock sample, wherein the lengths and the widths of the two straight cracks are equal to each other. The two straight cracks are arranged symmetrically. The loading moulds can achieve 45-degree loading of the sample with a loading end surface being flat and smooth. The widths of two contact surfaces between the loading moulds and the square rock sample are both half of the side length of the sample. An upper end and a lower end of the whole system are subjected to a uniform load. The method enables processing of the rock sample and the loading moulds to be more convenient, is simplified in test process, ensures accuracy of test data, is suitable for the II-type fracture toughness test of various rocks, and provides basis for researching the II-type fracture of rocks and a problem of composite fracture mainly comprising II-type fracture.

Description

Technical field: [0001] The invention relates to a method for testing rock type II fracture toughness. A shear fracture test is performed on a block rock sample on a conventional loading instrument to measure the type II fracture toughness of the rock. It belongs to the technical field of geotechnical engineering. Background technique: [0002] At present, for the tensile-shear composite cracks, the I-mode fracture toughness is mostly used to judge whether the cracked rock is damaged or not. For the compression-shear composite cracks, the results obtained using the I-mode fracture toughness as the failure criterion are different from the test results. is relatively large, which shows that this method is not applicable to the failure of composite compression-shear cracks, so it is very important to introduce mode II fracture toughness in the failure criterion of composite compression-shear cracks. [0003] So far, scholars at home and abroad have made a series of exploration...

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Problems solved by technology

[0005] The purpose of the present invention is to provide a new method for rock type II fracture toughness testing with easy operation, simple loading mold and rock sample processing, and high testing efficiency, which can effectively solve the cumbersome testing of the original shear cell test, complex loading mold processing, and theoretical problems. There is a large gap between the load on the model and the load on the actual loading model, and the asymmetry of the load causes a large tensile stress at the crack tip

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