• 한국자동차공학회논문집
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• 제6권4호
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• pp.121-128
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• 1998

In this study, when tension and bending stress act on plate simultaneously, stress intensity factor is analyzed at crack tip with using BEM(Boundary Element Method). In this analysis, stress intensity factors(S.I.F) are defined for variable ligament, aspect and stress ratio($\sigma$T/$\sigma$B). Consequently, predicted that crack grow to depth direction at low aspect and ligament ratio in tension stress and to surface direction in bending stress. Tension and bending stress act on plate same time, effect of tension stress in the first stage and effect of bending stress in the after stage was to observed. The outbreak of secondary crack in backside is under the control of stress amplitude and predict that the point of outbreak is mear backside.

• 대한기계학회논문집A
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• 제23권11호
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• pp.1904-1911
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• 1999

The most effective material in the shape memory alloy(SMA) is the TiNi alloy, because its shape recovery characteristics are very excellent. We molded the composite material with shape memory function. The fiber of it is $Ti_{50}-Ni_{50}$ shape memory alloy and matrix of it is epoxy resin(Araldite B41, Hardner HT903. Ciba Geigy), its adhesive and optical sensitivity are very excellent. It was assured that the composite material could be used as model material of photoelastic experiment for intelligent materials or structures. In this research, the composite material with shape memory function is used as model material of photoelastic experiment. Photoelastic experimental hybrid method is developed in this research, it is assured that it is useful on the obtaining stress intensity factor and the separation of stress components from only isochromatic data. The measuring method of stress intensity factor of intelligent material by photoelastic experiment is introduced. In the mode I state, we can know that stress intensity factors are decreased more than 50% of stress intensity factor of room temperature when temperature of fiber is greater than 4$0^{\circ}C$, prestrain greater than 5% and fiber volume ratio greater than 0.42% and that stress intensity factors are decreased by 100% when fiber volume ratio is greater than 0.84%, prestrain greater than 5% and temperature greater than 60 $^{\circ}C$.

• 대한기계학회논문집
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• 제16권1호
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• pp.63-69
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• 1992

본 연구에서는 특히 앞서 지적한 표면균열의 진전거동에 관한 연구와도 관련 하여 측면홈을 가진 중앙관통균열(side-grooved center cracked tension) 시험편에 대 해 피로균열 진전실험을 수행하고, 평면변형률 조건의 만족여부 및 응력강도계수 평가 방법에 관하여 검토하여 비교적 새로운 결과를 얻었으므로 여기에 보고하고자 한다.

• Steel and Composite Structures
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• 제20권4호
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• pp.951-962
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• 2016

The determination of the stress intensity factor at the crack tip is one of the most widely used methods to predict the fatigue life of aircraft structures. This prediction is more complicated for repaired cracks with bonded composite patch. This study is used to compute the stress intensity factor (SIF) and crack opening displacement (COD) for cracks repaired with single and double-sided composite patches. The effect of the presence of disbond region in adhesive at the crack was taken into consideration. The results show that there is a considerable reduction in the asymptotic value of the stress-intensity factors and the crack opening displacement at the crack tip. The use of a double-sided patch suppresses the bending effect due to the eccentricity of the patch on one side only.

• 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.

• Structural Engineering and Mechanics
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• 제18권6호
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• pp.759-768
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• 2004

The torsion of a penny-shaped crack in a transversely isotropic strip is investigated in this paper. The shear moduli are functionally graded in such a way that the mathematics is tractable. Hankel transform is used to reduce the problem to solving a Fredholm integral equation. The crack tip stress field is obtained by taking the asymptotic behavior of Bessel function into account. The effects of material property parameters and geometry criterion on the stress intensity factor are investigated. Numerical results show that increasing the shear moduli's gradient and/or increasing the shear modulus in a direction perpendicular to the crack surface can suppress crack initiation and growth, and that the stress intensity factor varies little with the increasing of the strip's height.

• 전산구조공학
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• 제10권1호
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• pp.129-134
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• 1997

탄성 섬유와 점탄성 기지로 구성된 2차원의 단일방향 복합재료에서 발생하는 계면 응력 특이성을 시간영역 경계요소법을 사용하여 조사하였다. 먼저, 아무런 균열없이 섬유와 기지가 완전하게 결합되어 있는 단일방향 복합재료에 횡방향 인장변형이 작용할때 자유경계면 부근에 나타나는 계면 특이응력들을 조사하였다. 그러한 응력들은 섬유와 기지의 결합분리나 계면 모서리 균열을 야기 시킬수 있다. 다음에, 여러가지 크기의 모서리 균열들에 대한 응력확대계수가 계산되었다.

• 한국해양공학회지
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• 제8권2호
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• pp.115-123
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• 1994

Under variable amplitude loading conditions, retardation or accelerated condition of fatigue crack growth occurs with every cycle, Because fatigue crack growth behavior varied depend on load time history. The modeling of stress amplitude with storm loading acted to ships and offshore structures applied this paper. The crack closure behavior examine by recording the variation in load-strain relationship. By taking process mentioned above, fatigue crack growth rate, crack length, stress intensity factor, and crack closure stress intensity factor were obtained from the stress cycles of each type of storm ; A(6m), B(7m), C(8m), D(9m), E(11m) and F(15m) which was wave height. It showed that the good agreement with between the experiment results and simulation of storm loads. So this estimated method of crack propagtion rate gives a good criterion for the safe design of vessels and marine structure.

• 한국자동차공학회논문집
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• 제1권2호
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• pp.117-124
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• 1993

This study is concerned with an application of the boundary element method on the crack problem. The stable and efficient analysis method of two dimensional elastostatic stress intensity factor on the mode I deformations is established from the result o stress analysis for the center cracked plates. In order to precisely analyse, The subelements of quadratic element, singular elements on the crack tip and interface and division into regions are applied to elastic stress. The usefulness of the method has been tested with a center cracked plates, a double edge cracked plate and a single edge cracked plate, and the results have turned out to be fairly satisfactory.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.123-128
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• 1998

In fracture problems, stress intensity factors obtained theoretically and experimentally have been effectively utilized in the analytical evaluation of the cracks effect. The effect of surface crack of a cylindrical and a hollow cylindrical bar is investigated, as well as the effect of the thickness of a hollow cylindrical bar and inclined crack of a hollow cylinder subjected to torsion moment. In this study, stress intensity factor Km of mode III which expresses the stress state in the neighborhood of a crack tip is used. Stress analysis was conducted of the inside of a hollow cylinder in the axial direction of three dimensional crack tip subjected to torsion moment by combining the caustics method and the stress freezing method.