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RISS 인기검색어
- 검색키워드
- 주제어 : rock indentation (검색결과 2 건)
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The rock fragmentation mechanism and plastic energy dissipation analysis of rock indentation
Zhu, Xiaohua,Liu, Weiji Techno-Press 2018 Geomechanics & engineering Vol.16 No.2
Based on theories of rock mechanics, rock fragmentation, mechanics of elasto-plasticity, and energy dissipation etc., a method is presented for evaluating the rock fragmentation efficiency by using plastic energy dissipation ratio as an index. Using the presented method, the fragmentation efficiency of rocks with different strengths (corresponding to soft, intermediately hard and hard ones) under indentation is analyzed and compared. The theoretical and numerical simulation analyses are then combined with experimental results to systematically reveal the fragmentation mechanism of rocks under indentation of indenter. The results indicate that the fragmentation efficiency of rocks is higher when the plastic energy dissipation ratio is lower, and hence the drilling efficiency is higher. For the rocks with higher hardness and brittleness, the plastic energy dissipation ratio of the rocks at crush is lower. For rocks with lower hardness and brittleness (such as sandstone), most of the work done by the indenter to the rocks is transferred to the elastic and plastic energy of the rocks. However, most of such work is transferred to the elastic energy when the hardness and the brittleness of the rocks are higher. The plastic deformation is small and little energy is dissipated for brittle crush, and the elastic energy is mainly transferred to the kinetic energy of the rock fragment. The plastic energy ratio is proved to produce more accurate assessment on the fragmentation efficiency of rocks, and the presented method can provide a theoretical basis for the optimization of drill bit and selection of well drilling as well as for the selection of the rock fragmentation ways.
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The Investigation of Rock Indentation Simulation Based on Discrete Element Method
Xiaohua Zhu,Weiji Liu,Xianqun He 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.4
Rock indentation is widely encountered in rock engineering, such as oil & gas drilling process. The rock indentation represents the fundamental process for mechanical rock breaking. Therefore, it is necessary to research the failure mechanism during the rock indentation process. For this purpose, the Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests are performed to calibrate the relations between micro-properties and macro-properties of the rock specimens. The rock indentation process and crack propagation with the effects of lateral pressure, hydraulic pressure, ledge, wedge angle and joint are researched by PFC2D in this paper. The results show that: with the indenter penetrating into rock, the sub-vertical crack is formed from the damaged zone and it will extend to bottom edge of the rock at last; the initiation and propagation of the sub-vertical crack is mostly driven by the tensile contact force. The development of sub-vertical crack and damaged zone are restrained with increasing lateral pressure, the lateral pressure increases led to an increase in the critical penetration depth and the size of the damaged zone decreases and its shape flattens with the lateral pressure increasing. On the contrary, the development of sub-vertical crack and damaged zone are promoted with increasing hydraulic pressure. With the wedge angle increases the size of crushed zone underneath the indenter increases, it promotes the formation of sub-vertical crack; larger wedge angle causes a larger indentation force. The existence of a ledge leads to crack initiation and propagation towards the free surface and the presence of the joint also promotes crack initiation and propagation towards the joint; when the crack propagates to the joint, the crack will no longer propagate towards the intact rock mass but along the joint.
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