• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.5 no.2
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• pp.27-34
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• 2009

This paper proposes a simple numerical method to simulate ductile failure behaviors. The method is based on finite element analysis with a simple damage theory. To validate the proposed method, simulated results are compared with experimental data. Despite its simplicity, the proposed method well predicts experimental results systematic analyses are also performed to investigate the effect of the element size.

• Proceedings of the KAIS Fall Conference
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• 2011.12b
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• pp.614-616
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• 2011

본 연구에서는 유한요소법과 변형률 의존성 연성파괴이론을 이용하여 드로잉 공정에서의 AZ31 마그네슘 합금 판재의 파단 발생을 예측 하였다. 다양한 온도에서의 사각컵 드로잉 실험을 수행하여, 각 온도조건에서의 파단깊이를 측정하였으며, 고온 인장시험을 통해 연성파괴상수를 온도 및 변형률 속도에 의존적인 값으로 표현하고, 실험과 동일하게 모사된 유한요소해석을 수행하였다. 해석결과 얻어진 각 요소의 온도 및 변형률 속도에 따른 연성파괴상수를 이용하여 파단발생을 예측하였으며, 실험결과와 검증하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.587-588
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• 2011

본 논문에서는 강사장교의 극한강도 및 파괴모드를 간략하게 예측할 수 있는 간단하고 빠른 해석법을 제안하였다. 기존의 비탄성 고유치해석의 기본 개념을 바탕으로 기둥 요소에 대한 수렴 기준을 보였고, 사장교 구조 시스템의 거더 및 주탑 요소에서 보-기둥 거동을 고려하기 위한 새로운 수렴 기준을 제시하였다. 제시된 방법의 타당성 검증을 위하여 중앙경간 길이와 거더의 높이를 변화시킨 강사장교 모델에 대하여 제안된 비탄성 고유치 해석과 비선형 탄소성 해석 결과를 비교하였다. 해석 결과, 제안된 수렴 기준을 적용한 비탄성 고유치 해석은 기존에 기둥의 수렴기준을 적용했던 방법에 비하여 강사장교의 극한강도를 보다 정확히 예측할 수 있었다. 또한, 제안된 방법은 강사장교의 파괴모드 역시 근사하게 모사 가능함을 알 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.15-23
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• 2002

For molecular dynamics requires high-performance computers or supercomputers to handle huge amount of computation, it is not until recent days that the application of molecular dynamics to materials fracture simulations draw some attention from many researchers. With the recent advent of high-performance computers, computation intensive methods become more tractable than ever. However, carrying out materials simulation on high-performance computers costs too much in general. In this study, a PC cluster consisting of multiple commodity PCs is established and computer simulations of materials with cracks are carried out on it via molecular dynamics technique. The effect of the number of nodes, speedup factors, and communication time between nodes are measured to verify the performance of the PC cluster. Upon using the PC cluster, materials fracture simulations with more than 50,000 molecules are carried out successfully.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.539-546
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• 2016

In this paper, the effect of J-R curve changes on the determination of parameters in a failure model owing to the presence or absence of a side groove in a C(T) specimen is investigated. A stress-modified fracture strain model is implemented for FE damage simulations. C(T) specimens were taken from SA508 grade 1a low-alloy steel piping material, and some of them were processed with a side groove. Fracture toughness tests were performed at room temperature and at $316^{\circ}C$. The parameters of the failure model were determined by damage simulations using the J-R curves obtained from the tests. Finally, the results show that the determination of failure model parameters is not affected by variations in J-R curves owing to the presence or absence of a side groove.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.469-485
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• 2016

The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.473-474
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• 2009

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.279-285
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• 2012

In this paper a computational method for a homogenized peridynamics description of unidirectional fiber-reinforced composites is presented. For these materials, dynamic brittle fracture and damage are simulated with the proposed peridynamic model. Compared with observations from dynamic experiments by Coker et al.(2001), the peridynamic computational model can reproduce various characteristics of dynamic fracture and supersonic or intersonic crack growth in asymmetrically loaded unidirectional fiber-reinforced composite plates. Also we analyze the same model in the symmetric loading condition and figure out that the asymmetric loading leads to a much higher propagation speed. Consistent results have been reported in the experiments.

• Tunnel and Underground Space
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• v.15 no.4 s.57
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• pp.250-263
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• 2005

Progressive and localized brittle failures around an excavated opening by the overstressed condition can act as a serious obstacle to ensure the stability and the economical efficiency of construction work. In this paper, the characteristics of the brittle failure around an circular opening with stress level was studied by the biaxial compressive test using sealed specimen and by the numerical simulation with $PFC^{2D}$, one of the discrete element codes. The occurring pattern and shape of the brittle failure around a circular opening monitored during the biaxial loading were well coincided with those of the stress induced failures around the excavated openings observed in the brittle rock masses. The crack development stages with stress level were evaluated by the detailed analysis on the acoustic emission event properties. The microcrack development process around a circular opening was successfully visualized by the particle flow analysis. It indicated that the scaled test had a good feasibility in understanding the mechanism of the brittle failure around an opening with a high reliability.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2007.03a
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• pp.112-121
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• 2007

지보재의 파괴가 고려된 터널의 안전율을 산정하기 위해 허용응력 설계법에 기초하여 숏크리트 내에 발생하는 응력이 허용응력을 초과하면 숏크리트가 파괴된다고 가정하고, 전단강도 감소기법을 이용하여 수치해석적(2차원)으로 구하는 방법이 유광호 등(2005)에 의해 제시되었다. 하지만 허용응력 설계법에 근거한 방법은 숏크리트의 허용 휨응력을 과소평가하여 터널의 안정성 및 안전율을 과소평가하는 경향이 있다. 따라서 본 논문에서는 숏크리트의 파괴거동을 갱도모형실험을 통해 확인하고 3차원 수치해석에 의해 검증하였다. 갱도모형실험에 사용된 터널은 실제 터널의 거동을 모사하기 위해 폭 3.3m, 높이 2.9m, 깊이 0.5m의 마제형으로 제작되었다. 지보재인 숏크리트는 거푸집을 이용하여 타설하고 28일간 양생하였고 7개의 실린더와 30cm의 모래 뒷채움을 이용하여 지보재에 최대한 등방하중이 가해질 수 있도록 하여 실험을 수행하였다.