Experimental Study On Propagation And Coalescence Of 3-D Coin Shape Cracks

Rock is a kind of non-uniformity material that usually contains a large number of defects, such as cracks and holes. Under the action of natural and man-made factors, these defects are deteriorated, which has serious influence on rock mechanical characteristics and failure mode, making the decrease of strength of rock mass, stiffness decreasing, or in severe cases, causing engineering geological disasters, such as rock-bust, collapse, landslide, etc. Therefore, studying the failure mechanism of cracking in crack mass has been the hot topic in engineering geology. In previous studies, most of its has been simplified as plane stress or plane strain problem. But essentially, both crack and rock itself have 3-D features, and the simplified methods will lead to loss of some important 3-D cracks propagation information. So, the study of 3-D cracks extension mechanism has grate significance to the design and construction of rock engineering.It is a very difficult job to prefabricate the 3-D cracks that has a certain geometric distribution in real rock material. The scholars at home and abroad usually adopt similar material to simulate the extension rule of 3-D cracks in brittle materials. Firstly, these materials should be similar to the rock. Secondly, it is easy to observe the propagation process of the crack inside of crack. In view of the above problems, this paper choose transparent organic glass(PMMA) to have uniaxial loading test, which studies the extension law of 3-D cracks. Specific work and main results are as follow:① In order to have a better analysis of the 3-D cracks propagation test results, this paper deduce the expansion length and the most favorable extension angle of the 2-D and 3-D cracks under uniaxial loading test.② According to the test purpose, choose organic glass(PMMA) as the test material, introduce the design and production process of specimens containing flaws, analysis the equipment that the test involves to easily operate the test and collect the date.③ Under the condition of uniaxial loading, study the crack extension mechanism of specimens containing 3-D single flaw(with different angles). Analysis the influence of crack angle on crack propagation mode and intensity rule. Compared with the propagation of 2-D single crack, the extension of 3-D cracks is more complicated under the condition of uniaxial loading. Some secondary cracks, such as flower porphyritic crack only in 3-D cracks extension can be observed.④ Study the crack extension mechanism of specimens containing 3-D double co-planar flaws(with different angles and distance) under the uniaxial loading. Analysis the influence of angle and distance on crack propagation mode and intensity change rule. Compare the test results to the same layout 2-D crack extension evolution process under the uniaxial loading.⑤ Study the crack extension mechanism of specimens containing 3-D three flaws(with different angle of rock bridge) under the uniaxial loading. Analysis the influence of angle of rock bridge on crack propagation mode and intensity change rule. Compare the test results to the same layout 2-D cracks extension evolution process under the uniaxial loading.