• International Journal of Automotive Technology
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• 제7권3호
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• pp.337-343
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• 2006

Numerical calculations are made in order to find a possible correlation between the J-integral and the crack mouth opening displacement(CMOD) in dynamic nonlinear fracture experiments of 3-point bend(3PB) specimens. Both elastic-plastic and elastic-viscoplastic materials are considered at different impact velocities. The J-integral may be estimated from the crack mouth opening displacement which can be measured directly from photographs taken during dynamic experiments.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.849-855
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• 2000

This study evaluated the effect of restraint of pressure induced bending(PIB) on crack mouth opening displacement(CMOD) for circumferential through-wall crack in pipe by using both elastic and elastic-plastic finite element analyses. The analyses results showed the restraint of PIB was decreased crack opening for a given crack length and tensile stress, and the effect was considerable for large crack and short restraint length. Also, the restraint effect on CMOD was independent on the variation in pipe diameter and decreased with increasing pipe thickness, and it depended on not total restraint length but short restraint length for non-symmetrically restrained. Additionally, the effect of restraint of PIB was more significant in the elastic-plastic analysis results compared with in the elastic analysis results.

• 한국정밀공학회지
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• 제11권2호
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• pp.134-140
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• 1994

Numerical caiculations are made in order to find a possible relation between the J-integral and the crack mouth opening displacement(CMOD) in dynamic nonlinear fracture experiments. Both elastic-plastic and elastic-viscoplastic materials are considered at different impact velocities. The J-integral may be estimated from the crack mouth opening displacement which can be measured directiy from photographs taken during dynamic experiments.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.215-220
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• 2001

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By varying strength and age, load-crack mouth opening displacement curves were obtained and the results were analyzed by linear elastic fracture mechanics. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete age from 1 day to 28 days. The obtained fracture parameters at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.191-198
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• 2006

The objective of this study is to examine fracture characteristics of concrete at early ages, i.g. critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of effective-elastic crack model and cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By experimenting with various strengths and ages, load-crack mouth opening curves were obtained, and the results were analyzed by linear elastic fracture mechanics and FEM(finite element method). The results from the test and analysis showed that critical stress intensity factor and facture energy increased while critical crack-tip opening displacement decreased with concrete aging from 1 day to 28 days. Four parameters of bilinear softening curve from 1 day to 28 days were obtained from a numerical analysis. The obtained fracture parameters and bilinear softening curves at early ages from this study are to be used as a fracture criterion and an input data for the finite element analysis of concrete at early ages.

• Computers and Concrete
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• 제4권1호
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• pp.49-66
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• 2007

The objective of this paper is to provide experimental data on the propagation of curved crack-surfaces and the respective load-displacement diagrams for the validation of numerical models for cracking of concrete, subjected to three-dimensional stress states. To this end beam-shaped specimens are subjected to combined bending and torsional loading, leading to the formation of a spatially curved crack-surface. The experimental data contain the evolution of the load and of the strains at selected points in terms of the crack mouth opening displacement and the propagation of the crack surface.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.125-130
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• 2002

The most important material parameters are fracture energy and the stress-crack opening displacement($\sigma$-w) curve to determine the behavior of concrete. Especially, the relationship between the $\sigma$-w curve is strongly important to determine the load-displacement curve of concrete that has a major influence on the fracture behavior of a concrete. In this paper, notched plain concrete beams with different strength level were tested under three-point bending and fracture energy, the load-deflection curve, and the load-crack mouth opening displacement(CMOD) curve were obtained from the experimental data. Also, the fictitious crack model(FCM) was applied to determine the load-deflection curve of notched plain concrete beams using various types of $\sigma$-w curve model proposed by Petersson and we compared experimental results with numerical ones carried out by Finite Element Method(FEM).

• 한국산학기술학회논문지
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• 제6권6호
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• pp.542-546
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• 2005

연성 크랙의 발생 평가를 위한 J-적분이 충격 하중을 받는 탄소성 3점 굽힘 시험편들에 대하여 연구한다. J-적분을 측정하고 평가하는 실험적인 방법이 연구되었으며 이 결과가 유한 요소법을 이용한 탄소성 이론 해석을 한 값들과 비교하여 거의 일치함을 보였다. 이론적인 수치 해석으로서도 본 연구의 유한 요소 모델로서 J-적분값을 계산할 수 있으며 삼점 굽힘 시험편의 동적 비선형 파괴 실험에 있어서 크랙 입구 개구 변위 (CMOD)에 의하여 J-적분값의 단순 계산이 가능함을 입증하였다. 탄소성 재료의 특성이 여러 가지의 충격 속도들에서 고려된다. J-적분은 충격 실험 동안 얻어진 사진들로부터 직접적으로 측정된 크랙 입구 개구 변위로부터 예측될 수 있다.

• 한국가스학회지
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• 제1권1호
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• pp.95-100
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• 1997

금속재료의 탄소성파괴인성치 측정을 위해서 ASTM E399 시험법에 따라 단순 인장 시험편을 사용하여 유한요소해석을 하였으며 여기에서 얻어진 하중-균열개구변위 곡선을 이용하여 균열개시점을 찾고 이 점에서의 파괴인성치 $J_{IC}$를 구하였다. 탄소성 파괴인성치 J 값은 J 적분법 및 M. K. Tseng등에 의해서 제안된 계산식을 이용하여 구하였다. 해석된 값의 검증을 위해서 고강도 저합금강인 AISI 4130 재료를 이용한 기존 실험값과 비교하였으며 그 결과는 잘 일치함을 알 수 있다.

• 콘크리트학회논문집
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• 제14권1호
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• pp.58-66
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• 2002

본 연구의 목적은 유효탄성균열모델과 점성균열모델의 개념에 기초한 임계응력확대계수, 임계균열단개구변위와 파괴에너지, 이선형 연화 곡선같은 콘크리트의 파괴특성들을 초기재령 콘크리트에 관해 구명하는 것이다. 이를 위해 모드 I의 파괴를 일으킬 수 있는 쐐기쪼갬시험이 노치가 있는 육각형의 쐐기 시험체에 대하여 수행되었다. 강도와 재령의 변화에 따라 하중-균열입구변위 곡선이 얻어졌으며, 이것은 선형탄성 파괴역학과 유한요소법에 의해 분석되었다. 실험 결과를 분석한 결과, 재령 1일부터 재령 28일까지의 임계응력확대계수와 파괴에너지는 증가하였으며, 임계균열단개구변위는 감소하였다. 또한 수치해석을 통하여 재령 1일부터 재령 28일까지의 이선형 연화 곡선의 네 파라미터를 구할 수 있었다. 이렇게 얻어진 초개재령 콘크리트의 파괴특성치와 이선형 연화 곡선은 초기재령 콘크리트의 파괴 기준과 유한요소해석시의 입력 상수로서 사용될 수 있을 것이다.