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- 주제어 : ductile-brittle failure (검색결과 3 건)
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연성 및 취성재료의 파괴이론을 고려한 위상최적설계 기법 개발
정승현(Seung-Hyun Jeong),박선호(Seonho Park),최동훈(Dong-Hoon Choi),윤길호(Gil Ho Yoon) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
This research develops a new stress-based topology optimization method (STOM) considering various static failure theories such as the maximum shear stress (MSS) theory, the distortion energy (DE) theory, the ductile Coulomb-Mohr (DCM) theory, and the modified Mohr (MM) theory. Although many TO methods considering the DE theory have been proposed, it seems that the TO method considering the other failure theories has not been proposed yet. In order to solve TO problem minimize the usage of material subject to various static failure criteria, we developed the differentiable failure criteria which use differentiable minimum and maximum operators. In addition, to achieve a stable TO process, the p-norm stress measure approximating the maximum value of the stress norms and the adjustment parameter in the segregated design domain are employed. The validity and usefulness of the present STOM are demonstrated by solving typical TO benchmark problems.
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A New Approach of Rock Cutting Efficiency Evaluation by using Plastic Energy Dissipation Ratio
Weiji Liu,Xiaohua Zhu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2
Polycrystalline Diamond Compact (PDC) bit is extensively used in oil & gas drilling, the rock cutting efficiency of PDC cutter directly determines the drilling efficiency and costs. Hence, it is crucial to evaluate the rock cutting efficiency of PDC cutters. The Mechanical Specific Energy (MSE) is used as an index for long periods of time to evaluate the rock cutting efficiency, however, the energy dissipation in rock breaking cannot be further calculated in details, leading to inaccuracy. To address this problem, the new concept of Plastic Energy Dissipation Ratio (PEDR) and its model are presented, a new approach for rock cutting efficiency evaluation by using PEDR is also put forward. Compared with MSE, the PEDR can determine the Optimum Depth of Cut (DOC) under various conditions. The theoretical analysis shows that the critical DOC, governing the transition of ductile to brittle failure mode, is the optimal cutting depth, having the smallest PEDR and highest rock cutting efficiency. The test and simulation of rock cutting are carried out to verify the PEDR model, and the PEDR under different DOC, cutting velocities and rake angles are depicted and discussed. The results can provide a theoretical basis for the design of PDC cutter and optimization of drilling parameters.
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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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