• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.301-308
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• 2001

The problem of predicting crack propagation in anisotropic solids which is a subject of considerable practical importance is examined. The effect of the second term in the asymptotic expansion of the crack tip stress field on the direction of initial crack extension is made explicitly. We employ the normal stress ratio theory to determine values for the direction of initial crack extension. The theoretical analysis is performed for the wide range of the anisotropic material properties. It is shown that the use of second order term in the series expansion is essential for the accurate determination of crack growth direction in anisotropic solids.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 추계학술대회 논문집
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• pp.471-472
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• 2009

• 전산구조공학
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• 제9권4호
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• pp.189-198
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• 1996

콘크리트 중력댐 상부면의 균열에 작용하는 수압의 영향을 주로 고려하여 댐의 파괴거동을 조사하였다. 첫째, 표면적분법에 의하여 응력확대계수를 구하는 경우에 작용하는 수압의 형태를 등분포형태 외에, 삼각형 분포 및 포물선분포도 고려하여 보았다. 둘째, FRANC(FRacture Analysis Code)를 이용하여 균열면에 작용하는 수압의 형태에 따른 기존균열의 전파방향을 추적하였다. 셋째, 월류수위 아래에서 균열이 전파되지 않을 수 있는 한계균열길이를 수압의 분포형태에 따라 구분하여 구하여 보았다. 표면적분법으로 수압의 형태에 따라 응력확대계수를 구한 결과는 FRANC를 이용하여 얻어진 결과와 비교 되었으며 비교적 잘 일치함을 알 수 있었다. 균열면에 작용하는 수압의 형태가 삼각형분포의 경우에 균열의 전파방향은 등분포의 경우에 비하여 댐의 기초쪽으로 기우는 것을 알 수 있었으며, 또한 월류수위 아래에서 한계균열길이는 댐높이의 대략 2/5-1/2되는 곳에서 최대가 됨을 알 수 있었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.644-649
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• 1993

Practical structures are subject not only to tension but also to shear and torsional loading. In this study, the mode 1 and 2 stress intensity factors of specimens were calculated by using elastic finite element mothod. The stress fields at the crack tip subjected to mixed-mode loading were also studied by usingf eleatic finite element method and were compared with theoretical results. The three-point-bending, four-point-bending, and mixed-mode-loading experiment were carried out. And, crack propagation rate da/dN and crack growth direction were examined. Also, the elastic finite element method was applied to calculate the stress intensity factors of branch crack tip and we relate the stress intenity factor range of branch crack tip(the result of FEM) to crack propagation rate(the experimental result). The .DELTA. -da/dN relation corelated with that of mode 1.

• 한국항공우주학회지
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• 제42권11호
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• pp.919-926
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• 2014

본 논문에서는 재료의 물성에 따른 파괴 거동을 응집영역모델과 확장유한요소법을 이용하여 예측하였다. 중앙에 경사진 초기 균열을 가지는 직사각형 시편 형상에 대해 평면응력요소로 모델링하고 인장하중을 가하여 균열의 전파 거동을 모사하였다. 파손 진전이 예측되는 지역에 대해 응집영역모델링 해석에서는 모든 일반 요소들 사이에 응집요소를 삽입하였고, 확장유한요소해석에서는 요소확장영역으로 지정하였다. 취성과 소성 재료에 대해 파괴 형태를 예측하고 파괴 강도를 계산하였다. 시편의 두께가 매우 얇은 경우에 기하학적 비선형 후좌굴해석 기법으로 주름변형을 고려하였고 주름이 파괴 거동에 미치는 영향을 조사하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.337-340
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• 2005

The effect of residual stress on fatigue crack growth was investigated in terms of finite element analysis. Simulations were performed on a CT specimen in plane strain. An interface-cohesive element that accounts for damage accumulation due to fatigue along the notch direction has been used. Numerical results show that fatigue crack growth rate slows down when compressive residual stress field exists in front of the crack tip.

• 대한기계학회논문집A
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• 제26권6호
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• pp.993-1000
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• 2002

The objective of this work is to develop the capability to analyze accurately the mixed-mode propagation of a crack in composite structures with elastic orthotropic material stiffness properties and anisotropic material strength characteristics. In order to develop the capability to fully analyze fracture growth and failure in anisotropic structures, we examined the fundamental problem of mixed mode fracture by carrying out the analysis on orthotropic materials with an inclined crack subject to biaxial loading. Our goal here is to include an additional term in the asymptotic expansion of the crack tip stress field and to show that the direction of crack initiation can be significantly affected by that term. We employ the normal stress ratio theory to predict the direction of crack extension. It is shown that the angle of crack extension can be altered by horizontal loads and the use of second order term in the series expansion is important f3r the accurate determination of crack growth direction.

• Advanced Composite Materials
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• 제16권2호
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• pp.151-166
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• 2007

High-cycle fatigue characteristics of quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates [-45/0/45/90]s up to $10^8$ cycles were investigated. To assess the fatigue behavior in the high-cycle region, fatigue tests were conducted at a frequency of 100 Hz, since it is difficult to investigate the fatigue characteristics in high-cycle at 5 Hz. Then, the damage behavior of the specimen was observed with a microscope, soft X-ray photography and a 3D ultrasonic inspection system. In this study, to evaluate quantitative characteristics of both transverse crack propagation and delamination growth in the high-cycle region, the energy release rate associated with damage growth in the width direction was calculated. Transverse crack propagation and delamination growth in the width direction were evaluated based on a modified Paris law approach. The results revealed that transverse crack propagation delayed under the test conditions of less than ${\sigma}_{max}/{\sigma}_b$ = 0.3 of the applied stress level.

• 한국안전학회지
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• 제14권2호
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• pp.19-25
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• 1999

The research has extracted two kinds of specimen, one is rolling direction material(R-material) and the other rectangular of rolling direction(V-material), from Al alloy 7075 rolled. We have come to a conclusion by measuring crack propagation behavior with movement type microscope and Replica. 1) R-material shows 130% higher, approx. 39.2MPa in fatigue strength than V-material, approx. 29.4MPa. 2) In crack proportion, contrary to V-material growing directly toward specimen axis, R-material grows neared to shear direction. 3) The life proves that R-material is approx. 122% higher than V-material at 43.1MPa and approx. 135% higher at 47MPa. 4) The correlation between fatigue crack length and fracture life ratio applied to 'log(2a)=A+B ($N/N_f$)'equation shows inappropriate, because property value of Al alloy is low and the difference of chemical composition is high comparing with steel material.

• Journal of Welding and Joining
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• 제6권2호
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• pp.30-39
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• 1988

Generally, as the welded region of weld structures has the incomplete bead and welded deposit which are able to behave like the surface cracks occasinally, there is a high possibility that the fatigue fracture of the weld structures is due to the surface cracks on the wlded region. This study was done to investigate the effects of post weld heat treatment (PWHT) on the fatigue behaviors of the surface crack of the heat affected zone (HAZ) for the multi-pass welds under the repetitive pure bending moment. The obtained results are summarized as follows : 1. The crack grows to the depth direction initially as the number of cylces increase, the amount of crack length is increased for the surface dir3ction and cive versa for the depth direction. 2. The fatigue life is increased in a order of as weld, PWHT specimens and parent. 3. As the number of cycles increase, the crack length is increased to th surface direction. The increase of the depth length is blunted at the center of specimen thickness. 4. The fatigue crack growth of PWHT specimens to the surface direction is dependent upon the holding time and applied stress during PWHT. In order words, the crack growth rate decreases with the holding time and increases with the applied stress during PWHT. 5. As the crack grows, the aspect formed in the course of crack propagation approaches to semicircle for parent and ellipse with the largest semidiameter for PWHT ($1/4hr, 15kgf/mm^2$) 6. At depth direction, it is difficult to apply to the paris' equation because of the scattered data between the crack growth rate and the stress intensity factor range.