• 한국안전학회지
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• 제11권2호
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• pp.9-15
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• 1996

The characteristics on the extension of the CED(Crack energy density) concept to the interface kinked crack problems in a dissimilar material are examined. Each mode contributions of CED are found by symmetric and antisymmetric components and domain independent integrals. Finite element calculation is carried out to simulate the Interface kinked crack growth on bimaterial. The focus is the establishment of fracture criterion with CED and finding the orientation of crack extension. From the results, a prediction about the extension behavior of an interface kinked crack can be done. And we show that CED can be a parameter to indicate fracture criterion at an Interface kinked crack.

• Composites Research
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• 제16권3호
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• pp.9-17
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• 2003

타이어 벨트층내의 코드간 균열연결 및 층간균열진전을 모사하기 위해 자유단을 갖는 2층 고무/코드 적층시험편에 대한 4~11mm 변위제어 실험을 수행하였다. 자유단의 코드간 균열연결시의 폭방향 균열진전량은 45$^{\circ}$ 경사진 코드들간 길이의 절반에 도달할 때의 측정값으로 하였으며, 이는 탐침법에 의해 측정되었다 또한, 자유단에서 코드들간 균열연결을 모사하기위해 2차원의 이상화된 모델링 기법을 고안하였다. 이론수명은 테어링에너지(균열파단면의 단위면적당 방출에너지)를 이용하여 코드간 균열연결수명(임계값)과 이후 최종파손까지의 수명으로 구분하였으며, 이들을 각기 실험값과 비교하였다. 임계값까지의 수명예측은 실험과 비교하여 약 20%, 최종파손까지 약 65%의 오차가 발생하였다. 따라서, 전체 이론수명은 실험과 비교하여 약 45%의 오차를 발생하였다.

• 항공우주시스템공학회지
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• 제17권2호
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• pp.1-8
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• 2023

회전익 항공기의 동력전달축은 경량화를 위하여 중공축을 적용하였으며 선형탄성 파괴역학을 이용해 균열 전파 거동을 예측할 수 있다. 본 논문에서는 유한요소해석을 통하여 원주방향 관통형 균열을 가지는 중공축의 균열성장수명을 예측하였다. 비틀림을 부여하고 균열을 고려한 요소를 형성하여 2차원 유한요소모델을 생성하였다. 초기 균열 길이를 정의하고 균열 길이를 증가시켜 유한요소해석을 수행해 균열 선단의 응력확대계수를 도출하였다. 응력확대계수가 중공축을 구성하는 재료의 파괴인성을 초과하기 직전의 길이를 한계 균열 길이로 정의한다. 응력확대계수 핸드북을 통해 응력확대계수를 계산하여 한계 균열 길이를 도출하고 균열성장속도식을 수치적분하여 각각의 균열성장수명을 비교해 제안한 유한요소해석 기법을 검증하였다.

• 한국안전학회지
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• 제9권1호
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• pp.161-164
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• 1994

Computer aided unloading elastic compliance method was employed to measure the closure and the length of short cracks. The most significant factor that influences the fatigue growth behavior of short cracks is the crack closure Phenomenon. dc/dN-$\Delta$ $K_{eff}$ relationships of short cracks are found to coincide well with the corresponding long crack relationships. Non-propagating behavior of short cracks at notch root can be predicted from the crack opening SIF of short cracks, $K_{op}$ , and the growth equation of long cracks in Region I and II.n Region I and II.I.

• 대한기계학회논문집A
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• 제24권9호
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• pp.2283-2291
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• 2000

The neural network method is applied to automatically measure the crack opening load under random loading. The crack opening results obtained are compared with the visual measured results. Fatigue crack growth under random loading is predicted using the crack opening data measured by the neural network method, and the prediction results are compared with experimental ones. It is found that the neural network method can be successfully applied to consistently measure the crack opening load under random loading and also gives some results different from the results by visual measurement.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1021-1026
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• 2003

The problem of predicting the fracture strength behavior in orthotropic plate with a crack inclined with respect to the principal material axes is analyzed. Both the load to cause fracture and the crack direction of crack growth arc of interest. The theoretical results based on the normal stress ration theory show significant effects of biaxial loading and the fiber orientation on the crack growth angle and the critical stress. The additional term in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.

• 한국정밀공학회지
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• 제13권8호
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• pp.80-87
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• 1996

The present paper will give some results of the fatigue behavior of typical axi-symmetric forward extrusion die. The extrusion process is analyzed by rigid-plastic FEM and the deformation analysis of extrusion die is conducted by elasto-plastic FEM. To approach the crack problem LEFM (Linear Elastic Fracture Mechanics) is introduced. Using special element in order to conside the sigularity of stress/ strain in the vicinity of the crack tip, stress intensity factor and the effective stress intensity factor is calculated. Applying proper fatigue crack propagation criterion such as Paris/Erdogan fatigue law and maximum principal criterion to these data, then, the angle and the direction of fatigue crack propagation is simulated. In result, it is proved that the simulated fatigue crack propagates in the zigzag path along the radial direction and fatigue life of the extrusion die is evaluated by using the computed crack growth rate.

• Structural Engineering and Mechanics
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• 제32권3호
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• pp.459-475
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• 2009

This paper presents analytical methodologies for remaining life prediction of plain concrete structural components considering tension softening and size effects. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. Size effect has been accounted for by modifying the Paris law, leading to a size adjusted Paris law, which gives crack length increment per cycle as a power function of the amplitude of a size adjusted stress intensity factor (SIF). Details of tension softening effects and size effect in the computation of SIF and remaining life prediction have been presented. Numerical studies have been conducted on three point bending concrete beams under constant amplitude loading. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature for all the tension softening models.

• 한국안전학회지
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• 제21권1호
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• pp.28-34
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• 2006

A procedure of estimating failure probability is demonstrated for a pressurized pipe of CrMo steel used at $538^{\circ}C$. Probabilistic fracture mechanics were employed considering variations of pressure loading, material properties and geometry. Probability density functions of major material variables were determined by statistical analyses of implemented data obtained by previous experiments. Distributions of the major variables were reflected in Monte Carlo simulation and failure probability as a function of operating time was determined. The creep crack growth life assessed by conventional deterministic approach was shown to be conservative compared with those obtained by probabilistic one. Sensitivity analysis for each input variable was also conducted to understand the most influencing variables to the residual life analysis. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• 한국자동차공학회논문집
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• 제4권4호
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• pp.130-139
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• 1996

The silicon carbide particles reinforced aluminium 6061($SiCp/A\ell$) composites are generally known have wild range of applications from automobiles to airospaces. But, by the results of existing study for $SiCp/A\ell$ composites, there are reports that the fatigue life of $SiCp/A\ell$ composites has improved than $A\ell$matrixes and has not improved then $A\ell$ matrixes. Consequently, in order to perform the reliable life prediction for $SiCp/A\ell$, the properties of probability distribution of fatigue crack initiation life & fracture life, crack growth length in constant number of cycles, crack growth rate in constant stress intensity factor range and m & C value in Paris's fatigue crack growth law and the estimation of statistical parameters have been evaluated by the statistics method.