• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.173-180
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• 2002

The specimens with three discontinuities have been tested in uniaxial compression. The geometry of discontinuities is changed by three different parameters: flaw inclination angle, continuity, and spacing. From the tips of the discontinuities wing and secondary cracks are observed. Wing cracks initially propagate curvilinear direction and follow loading direction after some distance from the tip of the discontinuities. Two different types of secondary cracks have been observed from the study: quasi-coplanar secondary cracks and oblique secondary cracks. From the test nine different types of coalescence are observed and they show a correlation with flaw angle and ligament angle. It is attempted to simulate the observed results by using FROCK(Fractured ROCK). FROCK is a code based on the hybridized DDM(Displacement Discontinuities Method) . It is shown that FROCK has quite potential of modeling of rock fracture processes.

• 비파괴검사학회지
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• 제23권3호
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• pp.189-197
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• 2003

Nucleation of a crack is readily defected by acoustic emission (AE) method. One powerful technique for AE waveform analysis has been developed as SiGMh (Simplified Greens functions for Moment tensor Analysis), as crack kinematics of locations, types and orientations are quantitatively determined. Because these kinematical outcomes are obtained as three-dimensional (3-D) locations and vectors, 3-D visualization is definitely desirable. To this end, the visualization system has been developed by using VRML (Virtual Reality Modeling Language). As an application, failure protest of a reinforced concrete beam is discussed.

• Journal of Welding and Joining
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• 제34권2호
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• pp.11-15
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• 2016

FE analyses for weldment of ship structure are required for various reasons such as stress concentration for bead tow, residual stress and distortion after welding, and hydrogen diffusion for prediction of low temperature crack. These analyses should be done by solid element modeling, but most of ship structures are modeled by shell element. If we are able to make solid element in the shell element FE modeling it is easily to solve the requirement for solid elements in weld analysis of large ship structures. As the nodes of solid element cannot take moments from nodes of shell element, these two kinds of element cannot be used in one model by conventional modeling. The PSCM (Perpendicular shell coupling method) can connect shell to solid. This method uses dummy perpendicular shell element for transferring moment from shell to solid. The target of this study is to develop a FE pre-processing system applicable at welding at ship structure by using PSCM. We also suggested glue-contact technique for controlling element numbers and element qualities and applied it between PSCM and solid element in automatic pre-processing system. The FE weldment modeling through developed pre-processing system will have rational stiffness of adjacent regions. Then FE results can be more reliable when turn-over of ship-block with semi-welded state or ECA (Engineering critical assessment) of weldment in a ship-block are analyzed.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1691-1701
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• 2006

The scan type magnetic camera is proposed to improve the limited spatial resolution due to the size of the packaged magnetic sensor. An image of the scan type magnetic camera, ${\partial}B/{\partial}x$ image, is useful for extracting the crack information of a specimen under a large inclined mag netic field distribution due to the poles of magnetizer. The ${\partial}B/{\partial}x$ images of the cracks of different shapes and sizes are calculated by using the improved dipole model proposed in this paper. The improved dipole model uses small divided dipole models, the rotation and relocation of each dipole model and the principle of superposition. Also for a low carbon steel specimen, the experimental results of nondestructive testing obtained by using multiple cracks are compared with the modeling results to verify the effectiveness of ${\partial}B/{\partial}x$ modeling. The improved dipole model can be used to simulate the LMF and ${\partial}B/{\partial}x$ image of a specimen with complex cracks, and to evaluate the cracks quantitatively using magnetic flux leakage testing.

• 한국전산구조공학회논문집
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• 제37권4호
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• pp.267-274
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• 2024

수소 취성 파괴는 수소가 풍부한 환경에 노출된 재료의 구조적 무결성을 보장하는 데 있어 다양한 산업 응용 분야에서 큰 도전 과제이다. 본 연구는 연성 파괴 모델인 Gurson-Cohesive 모델과 수소 확산 모델을 통합하는 수치 모델을 제안하고 수소 취화가 파괴 거동에 끼치는 영향을 조사한다. 사용된 연성 파괴 모델은 손상 진화를 모사하는 Gurson 모델과 균열 표면의 불연속성과 응력-균열폭 관계의 연화 거동을 설명하는 표면 요소 기반의 Cohesive zone 모델을 결합한 파괴 모델이며, 균열 시작 기준으로 공극과 삼축성을 고려한다. 또한, 파괴 모델과 통합된 수소 확산 분석은 수소 강화 탈결합(HEDE) 메커니즘과 그에 따른 균열 시작 및 진전에 미치는 영향을 고려하며, 응력-균열폭 관계에 대한 수소의 영향을 고려한다. 수치 예제로 매개변수 연구를 통하여 확산 계수와 수소 취화 파과 특성에 대한 민감도를 조사한다. 수소 확산 모델과 연성 파괴 모델을 통합한 프레임워크를 제시함으로써 본 연구는 수소 취화 파괴에 대한 이해를 제공하여 엔지니어링 응용 분야에서 기여할 수 있을 것이다.

• 한국전산구조공학회논문집
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• 제30권5호
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• pp.389-396
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• 2017

결합 기반 페리다이나믹 모델은 취성재료의 동적파괴 해석에 많이 이용되고 있으며, 최근의 연구(Bobaru et al., 2012)를 통해 적층유리 구조물의 동적 파괴 패턴 분석에도 활용되었다. 특히 실험(Bless et al., 2010)에서 나타난 적층유리 구조물의 다양한 손상 형태(압축 영역, Floret, Hertz-type 균열 등)를 결합 기반 페리다이나믹 시뮬레이션을 이용하여 구현하였다. 그러나 실제 적층 구조물은 각 유리판 사이를 탄성이 있는 층간 재료로 결합하는 반면, 기존의 페리다이나믹 수치 시뮬레이션에서는 층간 재료 결합을 무시하고 각 유리판이 직접 결속되도록 가정하여 층간 재료 효과가 무시되었다. 본 연구에서는 페리다이나믹 층간 재료 모델링을 통해 실제 적층 구조물에 보다 근접한 페리다이나믹 수치 해석 모델을 제안한다. 일반적으로 층간 재료는 매우 얇기 때문에 층간 재료를 명시적으로 모델링할 경우 많은 해석시간과 메모리가 소모되어 비효율적이다. 따라서 본 연구에서는 명시적 모델링을 대신하여 가상 절점을 통해 층간 재료를 모델링한다. 수치 예제를 통해 제안된 층간 재료 모델링의 효율성 및 정확성을 검토한다. 또한 압축 상태의 적층 구조물 해석을 위해 단거리 상호작용력에 기반한 투과 방지 기법을 도입하고 파라미터 테스트를 통해 검증한다.

• 대한토목학회논문집
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• 제32권6A호
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• pp.411-418
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• 2012

이 연구에서는 수치해석 실험을 통하여, 원주방향 관통균열을 갖는 원통형 쉘의 패치보강 전후의 거동에 대한 평가와 다양한 변수에 따른 패치보강 효과를 분석하였다. 해석 모델의 신뢰성을 높이기 위해, h-법 및 p-법에 기초한 모델링, 두 가지 방법이 동시에 고려되었다. 또한 선형탄성파괴역학 개념에 기초하여 에너지 방출률을 산정하기 위해, 등가영역적분법 및 가상균열확장법이 고려되었다. 해석 예제로서, 먼저 연구에서 수행된 h-법 및 p-법 유한요소 모델을 검증하기 위해, 패치 보강전의 인장력을 받는 관통 균열이 있는 쉘 구조물이 해석되었으며, 해석 결과값들과 여러 참고문헌 값들이 비교되었다. 그리고 패치 보강된 원통형 쉘 시스템에서의 접착제 두께, 접착제 전단탄성계수, 패치 두께, 패치 재료, 균열 길이 등의 여러 설계 변수에 대한 민감도 해석이 수행되었다.

• Geomechanics and Engineering
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• 제34권1호
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• pp.103-113
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• 2023

This study focused on understanding the relationship between the design of a tunnel boring machine disc cutter ring and its rock-breaking efficiency, as well as the applicable conditions of different cutter ring types. The discrete element method was used to establish a numerical model of the rock-breaking process using disc cutters with different ring types to reveal the development of rock damage cracks and variation in cutter penetration load. The calculation results indicate that a sharp-edged (V-shaped) disc cutter penetrates a rock mass to a given depth with the lowest load, resulting in more intermediate cracks and few lateral cracks, which leads to difficulty in crack combination. Furthermore, the poor wear resistance of a conventional V-shaped cutter can lead to an exponential increase in the penetration load after cutter ring wear. In contrast, constant-cross-section (CCS) disc cutters have the highest quantity of crack extensions after penetrating rock, but also require the highest penetration loads. An arch-edged (U-shaped) disc cutter is more moderate than the aforementioned types with sufficient intermediate and lateral crack propagation after cutting into rock under a suitable penetration load. Additionally, we found that the cutter ring wedge angle and edge width heavily influence cutter rock-breaking efficiency and that a disc cutter with a 16 to 22 mm edge width and 20° to 30° wedge angle exhibits high performance. Compared to V-shaped and U-shaped cutters, the CCS cutter is more suitable for soft or medium-strength rocks, where the penetration load is relatively small. Additionally, two typical case studies were selected to verify that replacing a CCS cutter with a U-shaped or optimized V-shaped disc cutter can increase cutting efficiency when encountering hard rocks.

• Structural Engineering and Mechanics
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• 제60권2호
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• pp.225-235
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• 2016

Fluid impact tests on plates containing mesh reinforcement and polypropylene fibers were modeled and simulated using explicit finite element analysis software, LS-DYNA. The scabbing dimensions obtained by the experiments and the simulations were compared and crack formations were matched. The objective was to test the accuracy and fidelity of the model and to confirm that damage caused by fluid impact on the plates can be estimated with a reasonable accuracy over a wide range of impact velocity.

• Structural Engineering and Mechanics
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• 제3권1호
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• pp.1-10
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• 1995

This study presents a methodology for the system reliability analysis of cracked structures with random material properties, which are modeled as random fields, and crack geometry under random static loads. The finite element method provides the computational framework to obtain the stress intensity solutions, and the first-order reliability method provides the basis for modeling and analysis of uncertainties. The ultimate structural system reliability is effectively evaluated by the stable configuration approach. Numerical examples are given for the case of random fracture toughness and load.