• 한국해양공학회지
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• 제11권3호
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• pp.29-38
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• 1997

Crack penetration behavior by fatigue crack propagation and measurements of AE before-and-after crack penetration were examined using SS41 steel plate. Experimental crack shape of SU type was in good agreement with calculated shape rather than S type. Crack propagation behavior on the front surface appears not to change markedly after penetration. However, crack growth on the back surface appears to accelerate as reported by author. As a crack propagates, AE occurred heavily just before penetration. Then, it decreases and crack is penetrating. A transition from plane strain to plane stress was observed by fractographic study. At this time, separation of fracture surface was shown which affects AE occurrence.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.19-24
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• 2000

Stress corrosion crack growth is simulated after assuming a small axial surface crack inside a S/G tube. Internal pressure and residual stresses are considered as applied forces. Stress intensity factors along crack front, variation of crack shape and crack growth rate are obtained and discussed. It is noticed that the aspect ratio of the crack is not depend on the initial crack shape but depend on the residual stress distribution.

• Nuclear Engineering and Technology
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• 제42권6호
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• pp.680-689
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• 2010

The crack-tip stress fields and fracture mechanics assessment parameters for a surface crack, such as the elastic stress intensity factor or the elastic-plastic J-integral, can be affected significantly by the adjacent cracks. Such a crack interaction effect due to multiple cracks can alter the fracture mechanics assessment parameters significantly. There are many factors to be considered, for instance the relative distance between adjacent cracks, the crack shape, and the loading condition, to quantify the crack interaction effect on the fracture mechanics assessment parameters. Thus, the current assessment codes on crack interaction effects (crack combination rules), including ASME Sec. XI, BS7910, British Energy R6 and API 579-1/ASME FFS-1, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates crack interaction effects by evaluating the elastic stress intensity factor and the elastic-plastic J-integral of adjacent in-plane surface cracks in a plate through detailed 3-dimensional elastic and elastic-plastic finite element analyses. The effects on the fracture mechanics assessment parameters of the geometric parameters, the relative distance between two cracks, and the crack shape are investigated systematically. As for the loading condition, an axial tension is considered. Based on the finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks are discussed. The present results can be used to develop more concrete guidance on crack interaction effects for crack shape characterization to evaluate the integrity of defective components.

• 한국구조물진단유지관리공학회 논문집
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• 제17권6호
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• pp.104-111
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• 2013

균열을 가진 콘크리트에서는 균열폭으로 유입되는 염화물 이온에 의해 열화가 가속화된다. 본 연구는 균열을 가진 콘크리트의 염화물 확산에 대한 모델링으로, 정상상태를 가정하여 1차원 (이방성) 및 2차원 (등방성) 균열 모델링을 수행하였다. 기존의 균열 모델링에서는 직사각형 균열패턴으로 모델링을 수행하였으나, 본 연구에서는 조도를 가진 쐐기형 형태로 균열을 모델링하였다. 검증을 위하여 1차원 유입에 대해서는 콘크리트 시편에 균열을 유입하여 염화물 영동실험을 수행하였으며, 2차원 유입에 대해서는 기존의 실험결과를 이용하여 검증을 수행하였다. 모든 경우에서 균열형태를 쐐기형으로 고려하여 염화물 확산성이 감소되었으며, 조도를 고려함으로서 합리적인 결과가 도출되었다. 특히 0.10~0.15의 조도계수를 고려할 때, 실험값에 가장 근접한 결과를 나타내었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.154-157
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• 2001

Through this study we investigated the causes of bottom crack. We then redesigned petaloid bottom to prevent bottom crack. We examined the material property variations according to the stretch ratio of PET and analyzed stretches of bottom in blowing processes. We also performed crack test to observe a crack phenomena. The effective stress and maximum principal stress were examined by computer simulation. We concluded that the bottom crack occurs because of not only insufficient strength of material due to the insufficient stretch of PET but also coarse design of petaloid shape. The highest maximum principal stress occurred at valley in petaloid bottom of bottle and this strongly affected the crack in bottom. We redesigned petaloid shape to minimize maximum principal stress, and this result in increasing the crack resistance.

• Structural Monitoring and Maintenance
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• 제1권3호
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• pp.309-322
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• 2014

Detection of fatigue cracks at an early stage of their development is important in structural health monitoring. The breathing of cracks in a structure generates higher harmonic components of the exciting frequency in the frequency spectrum. Previously, the residual operational deflection shape (R-ODS) method was successfully applied to beams with a single crack. The method is based on the ODSs at the exciting frequency and its higher harmonic components which consider both amplitude and phase information of responses to map the deflection pattern of structures. Although the R-ODS method shows the location of a single crack clearly, its identification for the location of multiple cracks in a structure is not always obvious. Therefore, an improvement to the R-ODS method is presented here to make the identification process distinct for the beams with multiple cracks. Numerical and experimental examples are utilised to investigate the effectiveness of the improved method.

• 디지털산업정보학회논문지
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• 제9권3호
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• pp.13-20
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• 2013

In this paper, we propose a multi-scale crack detection method. This method uses decomposition, composition, and shape properties. It is based on morphology algorithm, crack features. We use a morphology operator which extracts patterns of crack. It segments cracks and background using opening and closing operations. Morphology based segmentation is better than existing integration methods using subtraction in detecting a crack it has small width. However, morphology methods using only one structure element could detect only fixed width crack. Thus, we use decomposition and composition methods. We use a decimation method for decomposition. After decomposition and morphology operation, we get edge images given by binary values. Our method calculates values of properties such as the number of pixels and the maximum length of the segmented region. We decide whether the segmented region belongs to cracks according to those data. Experimental results show that our proposed multi-scale crack detection method has better results than those of existing detection methods.

• 대한기계학회논문집
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• 제8권2호
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• pp.141-144
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• 1984

본 연구에서는 완전 역 피로응력(completely reversed fatgue stress)를 받는 타원 노치에서 균열 발생과 전파에 대한 이론 임계 피로 한도를 응력 세기 계수 개념 을 도입하여 임의의 재질과 임으의 타원 노치 형상에 대해서 적용할 수 있도록 유도하 며 그 결과는 기존 이론보다 Frost의 실험치에 더 잘 일치함을 보이고자 한다.

• 수산해양기술연구
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• 제28권2호
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• pp.197-207
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• 1992

Fatigue life and penetration behavior were examined analytically by variety of initial front face crack length and initial crack depth. The fatigue crack shape before penetration is almost semielliptical, and the aspect ratio by calculation using the Newman-Raju's formula is smaller than the value obtained by the experiment. It is found that the crack growth behavior on the back surface after penetration is unique and can be divided into three stage a, b and c. By using the K value proposed by the authors, particular crack growth behavior and the change in crack shape can be evaluated quantitatively. It is found that fatigue life and penetration behavior were more dependent on initial front face crack length than initial crack depth.

• 한국강구조학회 논문집
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• 제11권4호통권41호
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• pp.409-416
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• 1999

반복하중을 받는 용접구조물의 피로수명 추정에 있어서 파괴역학을 이용한 피로균열 진전해석방법은 매우 유용하다. 휨응력을 받는 바닥강판의 피로균열 진전해석 문제에서는 균일한 축하중 하에서의 피로균열 진전해석 절차를 동일하게 적용할 수 있다. 본 연구에서는 휨응력하에서 피로균열 진전수명을 계산하는 방법을 제시하고 2차원 균열 문제에서의 피로균열 진전을 다루었다. 수치적으로 계산된 균열진전은 균열길이가 증가함에 따라 피로균열의 진전속도가 점차 감소하고 실험결과와 잘 일치하였다. 피로 수명은 초기균열길이와 균열형상에 따라 달라짐을 알 수 있었다.