• 한국측량학회:학술대회논문집
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• 한국측량학회 2007년도 춘계학술발표회 논문집
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• pp.165-168
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• 2007

A crack in concrete structure gives trouble to safety of building and human life. This study gives that development of auto extract system in a structure crack by digital image impersonal method for extract structure crack. This system will be possible to impersonal measurement for old concrete building and structure. For this auto extract system, used geometry of high resolution digital image and crack line extract by relation based image matching method. Now to conclude, this auto extract system gives a method that a quick measurement of building crack, hold objectivity in result, makes standardization for acquirement data, optimization result of measurement.

• Computers and Concrete
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• 제7권4호
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• pp.331-346
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• 2010

We present a quadrilateral finite element with an embedded crack that can be used to model tensile fracture in two-dimensional concrete solids and the crack growth. The element has kinematics that can represent linear jumps in both normal and tangential displacements along the crack line. The cohesive law in the crack is based on rigid-plasticity with softening. The required material data for the concrete failure analysis are the constants of isotropic elasticity and the mode I softening curve. The results of two well known tests are presented in order to illustrate very satisfying performance of the presented approach to simulate failure of concrete solids.

• 한국안전학회지
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• 제11권2호
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• pp.16-24
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• 1996

In this study we simulate the fatigue test of a compact tension specimen and obtain the displacements, stresses and strains by using the finite element method. And we examine the path independency of $\Delta$J integral values and compare it with $\Delta$J integral values calculated from load-load line displacement curve. From the results of this study, we can find that $\Delta$J integral show the path Independency for saturated materials. We can also find that the path independency of $\Delta$J Is not satisfied when different material Is assumed near the crack tip, but the difference in $\Delta$J is small. And $\Delta$J integral values calculated from load-load line displacement is very analogous with those from integration path but always have lower values than those from integration paths. In the case of crack closing, we found that $\Delta$J integral values from load-load line displacement should be calculated with the load Increment values based on the crack opening point. The unsaturated material is also simulated and its $\Delta$J shows different values according to the path, but the difference is small.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2989-2998
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• 2022

Line contact structures, such as the contact between graphite brick and graphite tenon, widely exist in high-temperature gas-cooled reactors. Due to the stress concentration effect, the line contact area is one of the dangerous positions prone to failure in the nuclear reactor core. In this paper, the failure mechanism of line contact structures composed of IG11 nuclear graphite column and brick were investigated by means of experiment and finite element simulation. It was found that the failure process mainly includes three stages: firstly, the damage accumulation in nuclear graphite material led to the characteristic yielding of the line contact structure, but no macroscopic failure can be observed at this stage; secondly, the stresses near the contact area met Mohr failure criterion, and a crack initiated and propagated laterally in the contact zone, that is, local macroscopic failure occurred at this stage; finally, a second crack initiated in the contact area and developed in to a Y-shape, resulting in the final failure of the structure. This study lays a foundation for the structural design and safety assessment of high-temperature gas-cooled reactors.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.583-586
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• 2000

In this paper, the embedded crack approach that crack is modeled by discontinuous line inside finite element is applied for localized progressive fracture analyses. The algorithm for progressive fracture analyses of concrete structure are enhanced by introducing nonlinear softening curve and unloading algorithm of tension-softening curve which can simulate localized fracture of concrete. The failure analysis results ar compared with existing test results for varification.

• 반도체디스플레이기술학회지
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• 제5권3호
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• pp.5-10
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• 2006

This paper investigates cutting qualities after laser dicing and predicts the problems that can be generated by laser dicing. And through 3 point bending test, die strength is measured and the die strength after laser dicing is compared with the die strength after mechanical sawing. Laser dicing is chiefly considered as an alternative to overcome the defects of mechanical sawing such as chipping on the surface and crack on the back side. Laser micromachining is based on the thermal ablation and evaporation mechanism. As a result of laser dicing experiments, debris on the surface of wafer is observed. To eliminate the debris and protect the surface, an experiment is done using a water soluble coating material and ultrasonic. The consequence is that most of debris is removed. But there are some residues around the cutting line. Unlike mechanical sawing, chipping on the surface and crack on the back side is not observed. The cross section of cutting line by laser dicing is rough as compared with that by mechanical sawing. But micro crack can not be seen. Micro crack reduces die strength. To measure this, 3 point bending test is done. The die strength after laser dicing decreases to a half of the die strength after mechanical sawing. This means that die cracking during package assembly can occur.

• 대한기계학회논문집A
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• 제21권1호
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• pp.124-132
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• 1997

This paper describes an experimental and numerical study on growing ductile crack-tip behaviors. The hybrid experimental and numerical method by means of a computer image processign technique, was applied to the analysis of both base metal and weld metal CT specimens. In the weld metal specimen, the initial crack-tip was placed in front of fusion line, and the crack orientation was perpendicular to it. Finite element analysis of crack growth behaviors in both base and weld matal specimens made of A533B Class 1 steel were also performed to examine the effects of weldment on near crack-tip fields. a series of experimental studies on crack-tip behaviors have clearly shown the qualitative effects of material properties, especially a hardening exponent. The experimental and numerical results have also shown that weldment does not affect displacement and strain fields near a crack-tip while a stress field is influenced by the difference between yield stresses of both base and weld metals.

• Structural Engineering and Mechanics
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• 제50권4호
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• pp.525-539
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• 2014

Bonded composite-patch repair has been widely used to restore or extend the service life of damaged structures due to its effectiveness as a mechanical repair technique. In this paper using extended finite element method (XFEM), three-dimensional crack models are developed to examine the fracture behavior of centrally cracked aluminum plates repaired with single and double sided composite patches. Stress intensity factor (SIF) at the crack tip is used as the fracture criterion. In this regard, the effects of the crack lengths, patch materials, orientation of plies, adhesive and patch thickness are examined to estimate the SIF of the repaired plate and the repair performance. The obtained results show that composite patches have significant effect on reduction of the SIF at the crack tip. It is also proved that using double symmetric repair, in comparison to single one, reduces considerably SIF at the crack tip. Hence, the residual strength can be improved significantly as well as fatigue life of the structure. Investigation of ply orientation effects shows SIF increase as the ply orientation is changed from $0^{\circ}$ (perpendicular to the advancing crack) to $90^{\circ}$ (parallel to the crack line). However, the effectiveness of the ply orientation depends on the loading direction and the crack direction.

• 대한기계학회논문집
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• 제11권5호
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• pp.740-745
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• 1987

본 연구에서는 파괴조건(4)와 유사하게 임계 스트레인 조건을 사용하나 기존 스트레인이 없는 재료의 날카로운 균열선단을 가진 시편의 파괴인성실험치(.delta.$_{IC}$)로 부터 재료의 고유상수인 특성길이를 결정하는 방법이 제안되었다.이 파괴조건을 이 용하여 처음노치선단의 유한한 반경과 재료의 기존 스트레인이 시편의 파괴개시에 미 치는 영향을 예측하고자 한다.

• 산업기술연구
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• 제35권
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• pp.3-8
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• 2015

A study has been made on defects which are formed in manufacturing processes of engine bearing and also on fatigue crack growth behavior in each step of bearing metal manufacturing. After the first step(sinter brass powder on steel plate ; Series A) many voids are made on brass surface and its size is decreased by the second step(rolling process of sintered plate ; Series B). After the third step(re-sintering step of brass powder and rolling ; Series C) the number of voids is decreased and its type shows line. The time of fatigue crack initiation and the growth rate of fatigue crack are in order of Series A, Series B, Series C. These reasons are that void fosters the crack initiation and growth, and residual stress made by rolling process effects on the crack growth rate in Series B, C. In forming and machining processes by use of final bearing metal, crack was observed at internal corner of flange and peeling off was observed at junction between steel and brass. Owing to the above crack and peeling off, it is considered that there is a possibility of fatigue fracture during the application time.