• 한국자동차공학회논문집
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• 제10권1호
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• pp.187-194
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• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

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

• 대한기계학회논문집A
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• 제26권5호
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• pp.828-834
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• 2002

In this paper, for the mixed mode fatigue problem, the method of determining testing load was proposed. It is based on the plastic zone size and the limited maximum stress intensity factor by ASTM STANDARD E 647-00. The application method of maximum tangential stress criterion and the stress intensity factor for the finite width specimen was proposed. In the result of applying the method to mixed mode fat gut test for A5052 H34, it obtained the satisfactory experimental results on the stable crack growth.

• 대한기계학회논문집
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• 제18권8호
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• pp.2158-2166
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• 1994

In order to understand the package crack emanating from the edge of leadframe after the delamination between leadframe and epoxy molding compound in an electronic packaging of surface mounting type, the M-integral and J-integral in fracture mechanics are obtained. The effects of geometry, material properties and molding process temperature on the package crack are investigated taking into account the temperature dependence of the material properties, which simulates a more realistic condition. If the temperature dependence of the material properties is considered the result of analysis conforms with observations that the crack is kinked at between 50 and 65 degree. However, in case of constant material properties at the room temperature it is found that the J-integral is underestimated and the kink crack angle is different form the observation. The effects of the material properties and molding process temperature on J-integral and crack angle are less significant that the chip size for the cases considered here. It is suggested that the geometric factors such as ship size, leadframe size are to be well designed in order to prevent(or control) the occurrence and propagation of the package crack.

• 콘크리트학회논문집
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• 제12권2호
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• pp.63-69
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• 2000

This study investigates a new method of using a concrete disk to calculate stress intensity factor (SIF) for mixed mode cases. The results indicate that the disk method is more accurate than three point bending test (TPB) in obtaining correct SIF values for mixed mode fracture propagation. Stress intensity factors $K_{I}$ and $K_{II}$ are calculated using a center notched disk subjected to splitting load. The notch angle is calculated by finite element (FEM). Fracture toughness $K_\textsc{k}$ of the concrete is obtained from the load intensities at the initiation of crack propagation. According to the finite element analysis(FEA) and disk test, the results show that mode I and mixed mode cracks propagate toward the directions of crack face and loading point, respectively. The results from FEA with maximum stress theory compare well with the experimental date. Unlike TPB method where an accurate fracture toughness value is difficult to obtain due to the irregular shape of load deflection curve and delayed final crack propagation (following slow stable cracking). fracture toughness value is easily measured in the disk test from the crack initial load. Therefore, it is safe to conclude that disk method is more advantageous than TPB method in analyzing combined mode fracture problems.

• 국제강구조저널
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• 제18권5호
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• pp.1589-1597
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• 2018

Fatigue tests and numerical analysis were carried out to evaluate the fatigue performance at the U-rib to deck welded joint in steel box girder. Twenty specimens were tested corresponding to different penetration rates (80 and 100%) under fatigue bending load, and the fatigue strength was investigated based on hot spot stress (HSS) method. The detailed stress distribution at U-rib to deck welded joint was analyzed by the finite element method, as well as the stress intensity factor of weld root. The test results show that the specimens with fully penetration rate have longer crack propagation life due to the welding geometry, resulting in higher fatigue failure strength. The classification of FAT-90 is reasonable for evaluating fatigue strength by HSS method. The penetration rate has effect on crack propagation angle near the surface, and the 1-mm stress below weld toe and root approves to be more suitable for fatigue stress assessment, because of its high sensitivity to weld geometry than HSS.

• 대한기계학회논문집A
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• 제28권3호
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• pp.281-288
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• 2004

The hybrid composite material (Al/GFRP laminates) are applied to the fuselage and wing in a aircraft. Therefore, Al/GFRP laminates suffer from the cyclic bending moments. This study was to evaluate the effect of fiber stacking angle on the fatigue crack propagation and delamination behavior using the relationship between crack growth rate (da/dN) and stress intensity factor range (ΔK) in Al/GFRP laminates under cyclic bending moment. The variable delamination growth behavior in case of three different type of fiber orientations, i.e., [Al/O$_2$/Al], [Al/+45$_2$/Al] and [Al/90$_2$/Al] at the interface of Al layer and glass fiber layer was measured by ultrasonic C-scan images. As results of this study, It represent that the delamination shape should turns out to have more effective characteristics on the fiber stacking angle. The extension of the delamination zone in case of [Al/+45$_2$/Al] and [Al/90$_2$/Al] were not formed along the fatigue crack profile. The shape of delamination zone depend on fiber stacking angle and the variable type with the delamination contour decreased non-linearly toward the crack tip at the Al layer.

• 콘크리트학회지
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• 제8권6호
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• pp.235-243
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• 1996

콘크리트의 역학적거동은 다양한 종류의 균열의 발생과 전파에 의하여 영향을 받는다. 최근 고성능 콘크리트의 개발이 이루어지면서 계면파괴와 계면역에서의 균열양상에 대한 연구가 중요한 분야로 부각되고 있다. 탄성이며 균질한 재료에 적용되는 균열전파에 대한 규준은 계면역에서 균열이 진전하는 경우는 유효하지 않으며 이 경우에는 콘크리트에서 균열전파를 예측하기 위하여 구성재료들의 파괴인성과 그들 사이 계면의 파괴인성의상대적인 크기를 고려하여야 한다. 본 논문에서는 계면균열선단에서 계면파괴역학변수인 에너지해방률과 하중위상각을 수치해석방법을 이용하여 구하는 방법과 계면에서의 균열전파의 예측을 위한 에너지해방률에 기초를 둔 파괴규준을 제안하였다. 계면역에서의 균열양상을 조사하기 위하여 계면균열을 가진 이상복합모델에 대한 실험과 수치해석연구를 수행하였으며 대체적으로 실험결과와 규준을 이용하여 예측한 결과가 서로 일치하는 결과를 얻었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.58-63
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• 2009

Biaxial compression test was conducted on a transversely isotropic synthetic jointed rock model for the understanding of the fracture behaviors of a sedimentary or metamorphic rocks with well developed bedding or foliation in uni-direction. The joint angles employed for the model are 30, 45, and 60 degrees to the horizontal, and the synthetic rock mass was made of early strength cement. From the biaxial compression test, initiation propagation of tensile cracks at norm to the joint angle was found. The propagated tensile cracks eventually developed rock blocks, which was dislodged from the rock mass. Furthermore, the propagation process of the tensile cracks varies with joint angle: lower joint angle model shows more stable and progressive tensile crack propagation. The experiment results were validated from the simulation by using discrete element method PFC 2D. From the simulation, as has been observed from the test, a rock mass with lower joint angle produces wider damage region and rock block by tensile cracks. In addition, a rock model with lower joint angle shows a progressive tensile cracks generation around the opening from the investigation of the interacted tensile cracks.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2000년도 암반공학문제의 수치해석(Numerical Analysis in Rock Engineering Problems)
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• pp.67-75
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• 2000

암석의 파괴인성 측정법으로서 최근에 연구되고 있는 Brazilian 파괴인성 시험을 PFC code를 이용하여 수치해석적으로 시뮬레이션하였다. 이로부터 가압면 형태, 시험편과 모델링 입자의 크기 관계, 가압면 각도 범위, 하중속도 등의 영향 변수에 대한 분석 및 적정 기준에 대해 검 토하였다. 균등한 하중 전달을 위해 가압면이 평면인 Brazilian 시험편을 도입하였는데, 시험편 중앙에서 초기 인장균열을 생성하고 파괴인성 산정에 필요한 안정한 인장균열 진전 시점의 임계하중이 나타나는 하중-변위 곡선을 얻을 수 있는 가압면 각도는 $20^{\circ}C$ -$40^{\circ}C$ 범위로 나타났다. 가압면 각도가 $20^{\circ}C$ 인 경우에, 디스크 시험편의 구성입자 반경이 1 mm 이하이고 하중속도가 0.01 mm/s 이하인 조건에서는 거의 일정한 파괴인성값을 얻을 수가 있었다. 가압면 각도가 $20^{\circ}C$이상이고 하중속도가 0.01 mm/s 이하는 파괴인성 측정에서 중요한 기본 조건인 시험편 중 에서의 인장균열 생성 및 이 인장균열의 안정적인 진전 제어를 위한 조건인 것으로 볼 수가 있다.