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.

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.

반복횡하중에 따른 철근콘크리트 모멘트골조의 거동 및 반응수정계수 분석

이수헌(Lee Swoo-Heon),신경재(Shin Kyung-Jae),김동백(Kim Dong-Baek),이희두(Lee Hee-Du) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.8

The average number of earthquake activities per year around the peninsula is about fifty times during the last five years according to the Korea Meteorological Administration. Nevertheless, the damage caused by the earthquake was not serious because the earthquake magnitude was not severe. It is required to make provision for old structural system with non-seismical detail at this time while the incidence of earthquake is gradually increasing. There are more than 80% school buildings of the reinforced concrete moment frame constructed before considering seismic design code in Korea. In this study, three RC frames designed only for gravity loads, including a frame simulated for non-seismical school building, were prepared based on KBC 2009: one ordinary moment frame (OMF) and two intermediate moment frames (IMFs). One of IMFs was strengthened with carbon fiber reinforced polymer (CFRP) at the base of column. A total of three frames were tested under cyclic loading according to ACI374.1-05. As a result, the CFRP increases the load-carrying capacity, ductility ratio and energy dissipation ratio but the strength and response modification factor were not increased as expected. Additionally, the plastic rotation of three models significantly exceeded the criteria of FEMA 356.

FRP 하이브리드 보강근을 가지는 RC보의 반복하중에 대한 역학적 성능 평가

황철성,박재성,박기태,권성준 한국구조물진단유지관리공학회 2017 한국구조물진단유지관리공학회 논문집 Vol.21 No.1

본 연구는 일반철근과 FRPH Bar를 주철근으로 한 철근 콘크리트 보부재를 대상으로 정적실험 및 반복하중 재하실험을 수행하여 에너지 소산성능 및 반복하중 저항성능을 분석하였다. 실험을 위하여 24MPa의 설계강도를 가진 콘크리트 보부재(200×200×2175mm)를 제작 하였으며, 4점 휨 시험을 수행하여 초기균열하중, 항복하중, 파괴하중을 측정하였다. 정적하중 재하실험을 통해 각 시험체에 대한 항복하중과 파괴강도를 측정하였는데, 항복하중은 RC보에서는 48.9kN, FRPH 보에서는 36kN으로 평가되었으며, 파괴하중은 두 시험체 모두 50kN의 강 도를 보였다. 정적하중-처짐 결과에서는 FRPH 보는 RC보에 비하여 인장경화특성을 나타내는데, 이는 FRPH bar의 인장경화 특성에 기인한다. 반복하중하에서 FRPH bar를 가진 보에서는 일반 RC보와는 다르게 작은 폭의 균열이 넓게 발생하였으며, 우수한 처짐 복원력을 나타내었다. 정적·동적 에너지 비율을 이용한 에너지 소산능력에서는 RC보에서는 0.62, FRPH 보에서는 0.83으로 평가되었으며, 이를 통해 FRPH를 가진 보부재에서 효과적으로 반복하중에 대하여 저항함을 알 수 있다. In the present work, a mechanical performances under cyclic loading in RC (Reinforced Concrete) beams with normal steel and FRPH (Fiber Reinforced Plastic Hybrid) bar are investigated. For the work, RC beam members with 200×200×2175 mm of geometry and 24 Mpa of design strength are prepared, and 4-point-bending tests are performed for evaluation of cracking, yielding, and ultimate loads. Through static loading test, 48.9kN and 36.0 kN of yielding loads are measured for normal RC and FRPH beam, respectively. They have almost same ultimate load of 50.0 kN. Typical tension hardening behavior is observed in FRPH beam, which is caused by the behavior of FRPH bar with tension hardening. In cyclic loading conditions, FRPH beam has more smaller crack width and scattered crack pattern, and it shows more elastic recovery than normal RC beam. The energy dissipation ratio in FRPH beam is 0.83, which is greater than 0.62 in normal RC beam and it shows more effective resistance to cyclic loadings.

GFRP 및 알루미늄으로 일체화된 복합 플레이트를 활용한 기둥래핑 내진보강

박춘욱,박익현 대한건축학회 2023 대한건축학회논문집 Vol.39 No.6

This study aims to assess the shear ability, ductility, and energy dissipation characteristics of specimens intended for jacket application,utilizing the wrapping method. The two specimens include the moment frame and the composite plate frame with a wrapping jacket. Theexperiments were conducted under the condition of simultaneous application of axial load and transverse force. The experimental results reflectvarious seismic resistance abilities of a structure, such as story-displacement ratio, stiffness, energy dissipation, and plastic rotation. Additionally, the results reveal the distribution of cracks and failures in extreme stages. 본 연구는 전단파괴가 예상되는 기둥 실험체에 구속형 보강재를 적용하여 전단능력 향상과 연성 및 에너지 소산능력을 평가하는데 목적이 있다. 이를 위해 축하중과 횡하중을 동시에 저항하면서 전단파괴가 예상되는 실험체를 제작하였으며, 구속형 복합 플레이트(Composite Plate)보강재를 적용한 실험체의 전단보강 성능을 확인하기 위하여 축하중과 동시에 횡하중을 적용한 가력실험을 수행하였다. 실험이 진행되면서 기록된 결과를 토대로 하중-변위 곡선을 작성하여 전단보강을 통한 기둥의 보강 효과를 비교·분석하였다.

변형지배거동을 하는 철근콘크리트 기둥의 에너지소산계수에 미치는 축력비의 영향 고찰

고관욱(Ko, Kwan-Wook),유석형(Yoo, Suk-Hyung) 대한건축학회 2024 대한건축학회 학술발표대회 논문집 Vol.44 No.1