Abstract
To accurately obtain the tensile strength of rock and fully understand the evolution process of rock failure is one of the key issues to the research of rock mechanics theories and rock mass engineering applications. Using direct tensile, Brazilian splitting, and three-point bending test methods, we performed indoor and numerical simulation experiments on marble, granite, and diabase and investigated the tensile strength and damage evolution process of several typical rocks in the three different tests. Our experiments demonstrate that (1) the strength is about 10% greater in the Brazilian splitting than in the direct tensile, while the tensile modulus is lower; it is the highest in the three-point bending, which is actually subjected to the bending moment and suggested as one of the indexes to evaluate the tensile strength of rock; (2) the strength in splitting tests is strikingly different, while the strain law is basically similar; the direct tensile test with precut slits is more attainable than that with no-cut slits, with an uninfluenced strength; (3) the failure modes of rocks using different methods are featured by different lithology, while their final modes are basically the same under the same method; (4) PFC and RFPA numerical simulation tests are effective to analyze the internal crack multiplication and acoustic emission changes in the rock as well as the damage evolution process of rock in different tests.
Highlights
As a quasibrittle material, rock is possessed of some basic mechanical parameters or strength indicators, including compressive strength, tensile strength, and shear strength, among which the tensile strength is much lower than the compressive strength
After observing the spatial tensile stress distribution in the Brazilian splitting test, Yu et al [12, 13] suggested that the splitting method was inapplicable to obtaining the tensile strength of rock materials, since the rock sample was inevitably cracked from the loading point under the influence of stress concentration, the original calculation formula was unsuitable for the three-dimensional elasticity test, and the calculated strength was underestimated for rock engineering design
To investigate the stress-strain characteristics of the rock samples at different positions and times in the direct tensile and Brazilian splitting tests, we paste the strain gauges at different positions when performing their loading with marble samples. eir stressstrain characteristic values are recorded and compared using the subsequent numerical simulation test. e specific test methods are shown in Figures 3 and 4
Summary
Rock is possessed of some basic mechanical parameters or strength indicators, including compressive strength, tensile strength, and shear strength, among which the tensile strength is much lower than the compressive strength. After observing the spatial tensile stress distribution in the Brazilian splitting test, Yu et al [12, 13] suggested that the splitting method was inapplicable to obtaining the tensile strength of rock materials, since the rock sample was inevitably cracked from the loading point under the influence of stress concentration, the original calculation formula was unsuitable for the three-dimensional elasticity test, and the calculated strength was underestimated for rock engineering design. With the improvement of the original Brazilian disc splitting test method in their study, Huang et al [15] analyzed the Brazilian platform splitting to determine the rock tensile strength, finding that the rock sample betters the central fracture failure for an optimal platform loading angle. Is to obtain their respective failure modes for the specimens and develop their particle models for the specimens in PFC3D and RFPA. en, it follows the comparison between the numerical and experimental results on the stress-strain curve of specimens and the discussion of the microcracks’ development of rock using the three methods by simulations
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