• Computational Structural Engineering
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• v.4 no.2
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• pp.77-85
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• 1991

A new finite element technology based on the p-version of E.F.M. is discussed with reference to its potential for application to stress intensity factor computations in linear elastic fracture mechanics, especially cracked cylindrical shells. It is shown that the p-version model is far better suited for computing the stress intensity factors than the conventional h-version models with the help of three test problems. The main advantage of this technology is that the accuracy of approximation can be established without mesh refinement or the use of special procedures such as crack-tip element and mixed variational approach.

• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.1-8
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• 2023

Power transmission shafts in rotary wing aircraft use a hollow shaft to reduce weight. We can apply linear elastic fracture mechanics to predict crack propagation behavior. This paper predicted crack growth life of a hollow shaft with a circumferential through-type crack by finite element analysis. A 2D finite element model was created by applying a torsion and forming elements considering cracks. We defined the initial crack length and performed the finite element analysis by increasing the crack length to derive stress intensity factor at crack tips. We defined the length just prior to the stress intensity factor exceeding the fracture toughness as the crack limit length. We calculated the crack limit length using a handbook and numerically integrated the crack growth rate equation to derive growth life of each crack. The growth life of each crack was compared to verify the proposed finite element analysis method.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.74-82
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• 1993

The present paper deals with the structural safety assessment techniques for independent type B spherical LNG tank against fatique crack initiation and propagation, which contains fellowing 3 steps. 1) Prediction of long term distribution of wave induced stresses and fatique crack intiation life using cumulative damage theory which were described at the 1st report. 2) Surface crack propagation analysis to verify that initial defects cannot penetrate tank plate. 3) Passing-through fatigue crack propagation analysis was performed based on LBF(Leak Before Failure ) theory.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.509-513
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• 2004

현장 균열망의 연결성 및 이에 따른 수리지질학적 특성을 규명하기 위하여, 기존의 통상적인 조사 기법을 한 지역에 집적하여 그 결과에 대한 통합해석을 수행하였다. 본 연구에 적용된 조사 방법은 양수시험, 물리검층, 다중심도 수리화학 분석, 전기비저항 토모그래피, 시추 코어 검층 등의 기련 특성 조사와, 추적자 시험, 다중 심도 수직 유향유속 시험 등 구간별 특성 조사 등이다. 이러한 조사 결과 본 조사 지역 내 균열의 전반적인 분포 특성을 확인할 수 있었으며, 각 균열의 수리적 특성에 대한 기본적 특성을 확인할 수 있었다. 특히 추적자 시험과 유향유속 시험 결과를 통해 각 관정간의 균열을 통한 연결성에 대한 중요한 정보를 도출할 수 있었다. 이러한 성과는 추후 percolation, connectivity 등 모델 개념의 현장화를 위한 연구의 선행 연구로서 그 의미를 자리매김 할 수 있을 것이다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.317-325
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• 2020

The development of a technique that can monitor the cracks, which is one of the typical types of damage, is necessary to secure the structural safety of elastically restrained cantilever-type beams with a tip mass that is used widely in infrastructure. Impedance techniques have been actively researched to detect cracks, and the cracks were estimated mainly by experimentally investigating the relationship between the crack and impedance signal. This study examined the correlation between the change in the impedance signals due to the crack, and the natural frequency obtained analytically. After updating the analysis model for the intact beam, the impedance signal was measured while gradually inflicting cracks in the cantilever-type beam, and the damage index was obtained. The results were compared with the natural frequencies calculated from the updated analysis model to investigate the correlation. A close correlation was observed between the experimentally obtained impedance damage index, and the analytically calculated natural frequency. Using this correlation, the structural characteristics could be evaluated more accurately from the damage estimation results, and the behavior of the structure could be predicted effectively using the analysis model.

• Tunnel and Underground Space
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• v.30 no.4
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• pp.306-319
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• 2020

Characterizations of Excavation Damage Zone (EDZ), which is hydro-mechanical degrading the host rock, are the important issues on the geological repository for the spent nuclear fuel. In the DECOVALEX 2019 project, Task G aimed to model the fractured rock numerically, describe the hydro-mechanical behavior of EDZ, and predict the change of the hydraulic factor during the lifetime of the geological repository. Task G prepared two-dimensional fractured rock model to compare the characteristics of each simulation tools in Work Package 1, validated the extended three-dimensional model using the TAS04 in-situ interference tests from Äspö Hard Rock Laboratory in Work Package 2, and applied the thermal and glacial loads to monitor the long-term hydro-mechanical response on the fractured rock in Work Package 3. Each modelling team adopted both Finite Element Method (FEM) and Discrete Element Method (DEM) to simulate the hydro-mechanical behavior of the fracture rock, and added the various approaches to describe the EDZ and fracture geometry which are appropriate to each simulation method. Therefore, this research can introduce a variety of numerical approaches and considerations to model the geological repository for the spent nuclear fuel in the crystalline fractured rock.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.611-617
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• 2018

The application of health monitoring, including a fault detection technique, is needed to secure the structural safety of large structures. A 2-step crack identification method for detecting the crack location and size of the beam structure is presented. First, a crack occurrence region was estimated using the modified Laplacian operator for the strain mode shape obtained from the distributed local strain data. The crack location and size were then identified based on the natural frequencies obtained from the acceleration data and the neural network technique for the pre-estimated crack occurrence region. The natural frequencies of a cracked beam were calculated based on an equivalent bending stiffness induced by the energy method, and used to generate the training patterns of the neural network. An experimental study was carried out on an aluminum cantilever beam to verify the present method for crack identification. Cracks were produced on the beam, and free vibration tests were performed. A crack occurrence region was estimated using the modified Laplacian operator for the strain mode shape, and the crack location and size were assessed using the natural frequencies and neural network technique. The identified crack occurrence region agrees well with the exact one, and the accuracy of the estimation results for the crack location and size could be enhanced considerably for 3 damage cases. The presented method could be applied effectively to the structural health monitoring of large structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.659-666
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• 2015

In this paper, various influence factors on the impact-echo test which is an effective method in characterizing defects such as such as the delamination in the concrete structures were studied. The side to thickness ratio(a/h), the relative position of impacting and sensing points over the delamination that have great effects on the flexural and impact-echo(thickness) modes were investigated and examined by the parametric finite element analysis. As a result, the flexural modes dominate in the case of a/h > 2 and the thickness mode was more evident when a/h < 2. With regard to the relative position of impact source and sensing point to the defect, the flexural modes dominate even when either the loading or sensing point was over the delamination defect. However, the thickness mode prevails when both the impacting and sensing points are over the solid region beyond the delamination area.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.4
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• pp.38-45
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• 1998

It is a tedious and excessive time consuming process to model the local area of crack tip part of structures in calculation of stress intensity factors by FEM. So, in this paper, the hybrid method of FEM and BEM approach was formulated to overcome this type of problems. The multi-domained BEM was adopted to simplify the modelling process of complex geometry and singularity characteristics of crack tip part and the ordinary FEM modelling was used in the rest part. The example calculations shows very good results compared with analytic solutions and other numerical method.

• Composites Research
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• v.20 no.5
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• pp.56-63
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• 2007

An approach using complex potentials is presented for analysis of composite plate with an elliptical hole or a rectilinear crack. Composite structure is susceptible to encounter impact damages, which lead to considerable decrease in its residual strength. Such impact damages could be modeled as an equivalent elliptical hole or notch-like crack. Even though finite element method is widely used to analyze stresses or fracture mechanics parameters around such damage, it is tedious to make successive FE-modeling for damage tolerance assessment under fatigue loadings. In this point of view, the solutions based on complex potentials are very simple and easy to use. The computed results are also compared and discussed with those from FEA.