• Tunnel and Underground Space
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• v.9 no.1
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• pp.56-63
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• 1999

Rock behaves in a complex way due to the discontinuities. To describe the complicated failure and deformation behavior of rock, many researches were focused on the development of crack models. This study discusses the validity of the sliding and shear crack model to systematically fractured rock, i.e. coal. The model was also implemented into a numerical analysis. For that, a finite element program was modified in several ways. To describe the transverse isotropy in two-dimensional analysis, the stress-strain relationship was modified for the direction of the axis of symmetry. Also, the changes of the effective elastic moduli according to the crack growth were calculated. A simple example of two-dimensional laboratory uniaxial compression test was analyzed. The results coincided with the observations obtained from the laboratory tests.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.270-288
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• 2021

We proposed a numerical method to simulate the hydro-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) in the paper. As a part of DECOVALEX-2023 Task G, we verified the method via benchmarks with analytical solutions. DECOVALEX-2023 Task G aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as a group of tetrahedral grains and calculated the interaction of the grains and their interfaces using 3DEC. The micro-parameters of the grains and interfaces were determined by a new methodology based on an equivalent continuum approach. In benchmark modeling, a single fracture embedded in the rock was examined for the effects of fracture inclination and roughness, the boundary stress condition and the applied pressure. The simulation results showed that the developed numerical model reasonably reproduced the fracture slip induced by boundary stress condition, the fracture opening induced by fluid injection, the stress distribution variation with fracture inclination, and the fracture roughness effect. In addition, the fracture displacements associated with the opening and slip showed good agreement with the analytical solutions. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.573-590
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• 2020

This study presents the current status of DECOVALEX-2023 project Task G and our research results so far. Task G, named 'Safety ImplicAtions of Fluid Flow, Shear, Thermal and Reaction Processes within Crystalline Rock Fracture NETworks (SAFENET)' aims at developing a numerical method to simulate the fracture creation and propagation, and the coupled thermohydro-mechanical processes in fracture in crystalline rocks. The first research step of Task G is a benchmark simulation, which is designed for research teams to make their modelling codes more robust and verify whether the models can represent an analytical solution for displacements of a single rock fracture. We reproduced the mechanical behavior of rock and embedded single fracture using a three-dimensional grain-based distinct element model for the simulations. In this method, the structure of the rock was represented by an assembly of rigid tetrahedral grains moving independently of each other, and the mechanical interactions at the grains and their contacts were calculated using 3DEC. The simulation results revealed that the stresses induced along the embedded fracture in the model were relatively low compared to those calculated by stress analysis due to stress redistribution and constrained fracture displacements. The fracture normal and shear displacements of the numerical model showed good agreement with the analytical solutions. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated using various experiments in a further study.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.593-609
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• 2021

We proposed a numerical method for the thermo-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) and simulated thermally induced fracture slip. The present study is the benchmark simulation performed as part of DECOVALEX-2023 Task G, which aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as an assembly of Voronoi grains and calculated the interaction of the grains (blocks) and their interfaces (contacts) using a distinct element code, 3DEC. Based on an equivalent continuum approach, the micro-parameters of grains and contacts were determined to reproduce rock as an elastic material. Then, the behavior of the fracture embedded in the rock was characterized by the contacts with Coulomb shear strength and tensile strength. In the benchmark simulation, we quantitatively examined the effects of the boundary stress and thermal stress due to heat conduction on fracture behavior, focusing on the mechanism of thermally induced fracture slip. The simulation results showed that the developed numerical model reasonably reproduced the thermal expansion and thermal stress increment, the fracture stress and displacement and the effect of boundary condition. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.11a
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• pp.21-31
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• 1991

대부분의 구조물은 정하중뿐아니라 동하중을 받고있으며, 반복되는 동하중에 의해 구조물은 피로를 받게되고 가장 취약한 부위에 작은 미시균열이 발생된다. 미시균열이 성장, 확산되어 기술적으로 인지되는 길이가 0.5 mm 이상이 될때 이를 거시균열이라 하는데, 거시균열의 균열성장은 파괴역학적 해석 방법의 도입으로 많은 공학적 재료들이 광범위하게 연구되었으며, 거시균열의 확산과 연관되어지는 균열닫힘과 미시구조의 관계가 연구되었다. 최근에는 거시균열의 해석과 같이 응력강도가 미시균열에서의 확산거동에 미치는 영향을 설명하는데 많은 관심을 가지게 되었다.(중략)

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.239-249
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• 2011

The behavior of the fiber reinforced concrete (FRC) base under environmental loads was analyzed numerically as a fundamental study to develop a high structural and functional performance composite pavement system in which the base was formed using FRC and the asphalt or cement concrete surface was placed on it. A two-dimensional finite element model of the FRC base was developed and the sensitivity study was performed with the variables including slab thickness of base, thermal expansion coefficient, elastic modulus, and tensile and compressive strengths. The crack spacing and crack width were selected as representatives of the base behavior. The effects of the selected variables on the crack spacing and crack width were analyzed and the sensitive variables were determined. The results of this study could be useful to determine the optimal material properties of the FRC base for combining well with the surface materials.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.121-125
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• 2018

In this study, finite element analyses of crack propagation along a sinusoidal interface are performed by using cohesive elements. BK law is used for cohesive zone to consider mixed mode traction-separation relation at the crack tip on a sinusoidal interface of a double cantilever beam specimen. The shape of a sinusoidal interface crack and the cohesive strength and the cohesive energies in mixed mode cohesive laws are varied in numerical experiments, and load-displacement curves at the ends of a double cantilever beam specimen are obtained to investigate the crack propagation behavior along a sinusoidal interface.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.48-57
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• 2007

The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by usiag the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.189-196
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• 1997

본 연구에서는 유한요소법을 이용한 콘크리트 인장균열의 발생 및 전파양상을 모형화하기 위하여 분산균열(smeared crack) 모델의 일종인 2차원 균질화된 균열(homogenized crack)모형을 제안하였다. 제안한 모형은 인장균열면을 따라 속도 불연속계(velocity discontinuity)를 도입하고 평형방정식 빛 적합방정식을 이용하여 인장균열을 포함한 콘크리트의 구성방정식을 유도할 수 있으며 인장균열이 소성연화거동을 하는 경우. 유한요소망내에서 객관성이 유지될 수 있음을 밝히기 위하여 1차원 영역내에서 엄밀해를 유도하였다. 제안한 모형을 이용한 1차원 또는 2차원 유한요소 해석은 기존의 노치를 포함한 콘크리트 시편에 대한 실험과 상응하는 결과를 보였을 뿐만 아니라 유한요소망의 객관성이 유지되고 있음을 밝혔다. 제안한 모형은 큰 어려움없이 3차원 영역으로 확대할 수 있을 것이며 이에 대한 추가적인 연구가 계속될 것이다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1990-2001
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• 1991

The fatigue life and crack penetration behavior of high strength steel have been studied in detail both experimentally and analytically. The fatigue crack shape of a smooth specimen is almost semicircular, while a specimen with stress concentration becomes semielliptical according to stress concentration shape. The aspect ratio of smooth specimens calculated using the Newman-Raju's formular is smaller than the value obtained from the experiment. On the other hand, the aspect ratio of the stress concentration specimen shows a good agreement with experimental results. It is found that the crack growth behavior on the back surface after the penetration is unique and can be divided into three stages ; rapid growth region, constant growth region and acceleration growth region. By using the K value suggested in this study, the particular crack growth behavior and crack shape can be estimated quantitatively.