• Structural Engineering and Mechanics
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• 제2권3호
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• pp.227-244
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• 1994

The purpose of this investigation is to propose a numerical simulation method of the crack propagation behavior in 3-dimensionl elastic body. The simulation method is based on the displacement-type finite element method, and the linear fracture theory is introduced. The results from the proposed method are compared with those from the structural experiments, and the good coincidences between them are shown in this paper. At the same time, 2-dimensional analysis is also done, and the results are compared with those obtained from 3-dimensional analysis and the structural experiments.

• 대한기계학회논문집A
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• 제30권6호
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• pp.722-727
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• 2006

Bone fracture healing is one of the important topics in biomechanics, demanding computation simulations due to the difficulty of obtaining experimental or clinical results. In this study, we adopt the design space optimization method which was established by the authors as a tool for the simulation of bone growth using its evolutionary characteristics. As the mechanical stimulus, strain energy density is used. We assume that bone tissues over a threshold strain energy density will be differentiated and bone tissues below another threshold will be resorbed. Under compression and torsion as loadings, the filling process of the defect is well illustrated following the given mechanical criterion. It is shown that the design space optimization is an excellent tool for simulating the evolutionary process of bone growth, which has not been possible otherwise.

• 한국안전학회지
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• 제21권1호
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• pp.28-34
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• 2006

A procedure of estimating failure probability is demonstrated for a pressurized pipe of CrMo steel used at $538^{\circ}C$. Probabilistic fracture mechanics were employed considering variations of pressure loading, material properties and geometry. Probability density functions of major material variables were determined by statistical analyses of implemented data obtained by previous experiments. Distributions of the major variables were reflected in Monte Carlo simulation and failure probability as a function of operating time was determined. The creep crack growth life assessed by conventional deterministic approach was shown to be conservative compared with those obtained by probabilistic one. Sensitivity analysis for each input variable was also conducted to understand the most influencing variables to the residual life analysis. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• 대한기계학회논문집A
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• 제29권1호
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• pp.81-87
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• 2005

A fracture of hand held device, such as radio, TV and CD-RW drive, mainly occurs due to drop situation. For CD-RW drive, the need of high reading/writing speed in conjunction with low price accelerates the fracture of the device. Computer simulation can reduce the period of development and enhance impact characteristic of device. In this study, the detailed finite element model of CD-RW drive was developed to predict the damage under drop conditions. Material property for shock absorbing damper was obtained from tensile test of raw material. A MOONEY-RIVLIN type rubber in LS-DYNA was used as the material model of damper. To assess the reliability of the developed model, drop test at 200G-2msec and 150G-10msec condition was conducted and acceleration at pick-up was compared.

• 대한지하수환경학회지
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• 제6권3호
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• pp.111-119
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• 1999

본 연구는 방사성 폐기물 처분부지의 안정성 평가검증을 위한 균열 암반내 지하수리시스템 특성연구의 일환으로 균열암반모사 및 균열망 특성을 규명하는 것으로 지하 심부에 위치하게 되는 방사성폐기물 처분부지와 입지조건이 유사한 LPG 지하비축기지를 대상으로 균열 및 수리지질특성의 규명과 연속체 모델과 불연속체 모델의 적용을 통한 지하수 유동로 해석을 실시하였다. 불연속체 모델을 통한 지하수 유동 및 용질 이동의 모사에는 균열의 방향성과 균열의 공간적 밀도가 가장 중요한 요소인 것으로 나타났다. 본 연구지역에서는 3조의 균열군이 조사되었으며 균열의 공간적 밀도( $P_{32}$)는 0.85 $m^2$/㎥로 나타났다. 프로판 공동주변의 모사영역(200$\times$200$\times$200 m)에 대하여 실제로 지하수의 유동에 관여하는 투수성 균열의 밀도( $P_{32c}$)를 모사한 결과는 0.536 $m^2$/㎥로 나타났으며. 저투수성인 균열을 제거함으로서 0.26 $m^2$/㎥의 균열밀도(T- $P_{32c}$)를 갖는 모델을 재구성하여 수압터널로부터 PC 2. PC 3의 프로판 주공동으로의 유동로 분석을 실시하였다.다.

• 대한기계학회논문집A
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• 제40권8호
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• pp.693-701
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• 2016

본 논문에서는 파괴역학적 방법으로 노치 결함을 평가해 보았다. 인장 하중과 굽힘하중이 작용하는 중앙 균열, 모서리 균열 평판 구조물을 바탕으로 노치 크기를 달리하며 한계하중 및 에너지해방률을 유한요소 해석의 J-적분으로 도출하였다. 노치의 반경이 커짐에 따라 한계하중은 큰 변화가 없었으며, 에너지해방률는 커지는 양상을 보였다. 노치 반경에 따른 재료 파괴인성($J_{IC}$)측정을 위해 실험을 대신한 유한요소 연성파손 모사기법을 사용하였다. 그 결과 노치 크기 증가에 따른 에너지해방률 증가량 대비 파괴인성($J_{IC}$) 증가량이 더욱 큰 양상을 보였다. 이런 결과를 통해 노치 반경이 커질수록 균열 진전에 대한 저항성이 커진다는 사실을 알 수 있었다.

• 대한기계학회논문집A
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• 제38권2호
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• pp.105-113
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• 2014

중앙에 균열을 갖는 단층 그래핀시트(single layer graphene sheet, SLGS)의 모드 II 파괴 거동을 원자 시뮬레이션과 해석 모델에 기초하여 고찰하였다. 지그재그 그래핀 모델의 파괴를 분자동역학(molecular dynamics, MD)에 의해 해석한 결과 모드 II 파괴인성은 $2.04MPa{\sqrt{m}}$인 것으로 밝혀졌다. 또한 SLGS의 이론적인 $K_{IIc}$를 유도하기 위해 면내전단하중을 받는 다공체에 대한 파괴역학적 해석도 진행하였고 유한요소해석도 병행하였다. 모드 I과 모드 II의 비를 다양하게 변화시켜가면서 SLGS 의 혼합모드 파괴를 검토한 결과 혼합모드 파괴조건식이 얻어졌고 다른 문헌의 결과와 비슷함을 알 수 있었다.

• 동력기계공학회지
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• 제8권4호
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• pp.11-16
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• 2004

In this study, to investigate the effects of omitting low-amplitude cycles from a flight-simulation loading, crack growth tests were conducted on 2124-T851 aluminum alloy specimens. Three test spectra were generated by omitting small load ranges as counted by the rain-flow count method. The crack growth test results were compared with the data obtained from the flight-simulation loading. The experimental results show that the ranges equal to or smaller than 5% of the maximum load do not contribute to crack growth behavior because these are below the initial stress intensity factor range. Omitting these from the flight-simulation loading, test time can be reduced by 54%. However, in the case of omitting the load ranges below 15% of the maximum load, crack growth rates decreased, and crack growth curve deviated from the crack growth data under the flight-simulation loading because loading cycles above fatigue fracture toughness were omitted.

• Computers and Concrete
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• 제20권1호
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• pp.39-47
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• 2017

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, the simulated models in five introduced indirect tests were cross checked with the results from direct tests. By using numerical testing, the failure process was visually observed. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Mode I fracture toughness of rock in direct test was less than other tests results. Fracture toughness resulted from semi-circular bend specimen test was close to direct test results. Therefore semi-circular bend specimen can be a proper test for determination of Mode I fracture toughness of rock in absence of direct test.

• 소성∙가공
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• 제18권1호
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• pp.59-66
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• 2009

In this study, V-notch part has been considered as one of safety components in rectangular cup used for mobile device. This kind of safety component in rectangular cup with the V-notch part, which controls adequately the increased internal pressure in the rectangular cup, plays an important role to prevent the explosion from the excessive internal pressure. The protecting mechanism on the mobile device against the explosion is that a series of fracture on the V-notch part at the critical internal pressure level occurs. Therefore, it is very crucial to estimate accurately the working pressure range of the safety device. Relationship between the working internal pressure and fracture phenomenon at V-Notch part was investigated through numerical analysis using ductile fracture criteria. Integral value, I, of the used ductile fracture criteria was calculated from effective stress and strain, and then the bursting pressure of the V-notch part was extracted. Comparisons between the estimated and experimental results show that this systematic approach to predict bursting pressure using the ductile fracture criteria gives fairly good agreements.