• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.59-68
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• 1987

Several series of fracture tests were conducted to explore the fracture characteristics and to determine the fracture energy of concrete. A stable three-point bend test was employed to generate the load-deflection curves. The fracture energy may then be calculated from the area under the complete load-deflection curve. The initial notch-to-beam depth ratio (${\alpha}_0$/H) was varied from zero to 0.6. The prediction formula for the fracture energy of concrete is also derived and is found to depend on the tensile strength and aggregate size. The proposed fracture energy formula can be used for the fracture analysis of concrete structures. The present study also devises an equivalent crack length concept to predict the maximum failure loads of concrete beams. A simple formula for the equivalent crack length is proposed.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.111-121
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• 1997

An investigation was performed to study the predicting the joint strength of mechanical fasteners. Bearing failure is most important failure mode for designing joint. So in this study, the prediction method in consideration with bearing failure was chosen. In the proposed method, the characteristic length is combined with the Yamada-Sun failure criterion, Tsai-Hill failure criterion and characteristic length for Tension and Compression is determined from investigation. Especially the length of compression is determined from the "bearing failure test" that newly conceived to take bearing failure into consideration. The proposed prediction method was applied to quasi-isotropic carbon/epoxy joint showing net-tension and bearing failure experimentally. Good agreement was found between the predicted and experimental result for each joint geometry. geometry.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.269-279
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• 1997

An investigation was peformed to study the predicting the joint strength of mechanical fasteners. Bearing failure is most important failure mode for designing joint. So in this study, the prediction method in consideration with bearing failure was chosen. In the proposed method, the characteristic length is combined with the Yamada-Sun failure criterion, Tsai-Hill failure criterion and characteristic length for Tension and Compression is determined from investigation. Especially the length of compression is determined from the "bearing failure test" that newly conceived to take bearing failure into consideration. The proposed prediction method was applied to quasi-isotropic carbon/epoxy joint showing net-tension and bearing failure experimentally. Good agreement was found between the predicted and experimental result for each joint geometry.

• Tunnel and Underground Space
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• v.7 no.2
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• pp.143-149
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• 1997

암석의 파괴인성계수(fracture toughness)는 균열의 성장에 대한 암석의 저항을 나타낸다. 실험실에서 측정한 파괴인성계수는 일반적인 암석의 불균질성이나 이방성 외에도 시험편의 형상이나 하중조건에 의하여 크게 영향을 받는다. 따라서, 제한된 수의 시험편을 사용하여 측정된 파괴인성계수는 자료의 분산이 심하므로 실제 적용에 있어서 문제가 된다. 균열감응도란 파괴인성계수의 측정에 사용되는 시험편의 형상에 따라 결정되는 지수로서, 시험편의 파괴가 균열의 성장에 의한 것인지, 혹은 인장강도에 의한 것인지를 판별하는 기준이 된다. 이러한 균열감응도를 파악하여 암석의 파괴인성계수 측정에 유효한 시험편의 크기나 초기균열 길이의 범위를 설정할 수 있다. 이는 또한 실험실에서 측정된 차괴인성계수의 유효성 여부를 판별하는 기준으로 사용될 수 있다. 본 논문에서는 암석의 파괴인성계수의 측정에 흔히 사용되는 몇 가지 형태의 시험편들에 대하여 균열감응도를 계산하고 이에 따른 초기균열 길이의 범위를 제시하고자 한다.

• Magazine of the Korea Concrete Institute
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• v.9 no.6
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• pp.157-164
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• 1997

최근 손상된 구조물에 탄소섬유쉬트 보강공법이 많이 사용되고 있다. 탄소섬유쉬트 보강에 따른 휨내력의 증진이 이루어지기 위해서는 보와 탄소섬유쉬트의 일체거동이 이루어져야 하며, 쉬트단부에서 부착파괴가 발생하지 않아야 한다. 따라서 이번 실험에서는 탄소섬유쉬트의 보강매수에 따른 부착파괴의 거동을 살펴보았다. 전시험체에서 부착파괴가 발생하였으며 부착파괴가 발생한 하중의 크기는 보강매수에 관계없이 비슷하였다. 부착파괴의 거동은 순수부착파괴와 피복박리파괴로 구분될 수 있었으며 부착응력은 단부에서 집중현상이 나타났고 집중된 응력의 크기는 15.39~41.42kg/$\textrm{cm}^2$로 나타났다. 정착길이내의 평균부착응력은 6.85~8.99kg/$\textrm{cm}^2$으로서 평균 7.38kg/$\textrm{cm}^2$이고 이 값은 이론치인 6.19kg/$\textrm{cm}^2$보다 약간 높으며 설계부착응력인 6kg/$\textrm{cm}^2$에 부합되는 것으로 나타났다. 따라서 설계부착응력 6kg/$\textrm{cm}^2$은 정착길이의 설계시 합리적 값으로 평가되었다.

• Magazine of the Korea Concrete Institute
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• v.6 no.1
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• pp.131-141
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• 1994

This experimental study was performed to lnvestigate the effects of the lergths dnd volume contents of glued hooked steel fiber for the fracture toughness and strength of c oncretc. The notched steel fiber reinforced concrete beams with different flber length(30, 60mm) and fiber volume content(O.0, 0.5, 1.0, 1.5, 2.0%) were tested under 3-point benclmg, md 1 he flexural strengths, fracture energy and CMOD were obtained from the experimental data. The fracture energy v~ds used as d means to evaluate the fracture toughness ot concrete. The results showed that the frdcture toughness and 5trength of conuett. were generally increased ds the content of steel fiber was inc~edsed, arid the length of steel ilber had a great efiect on the flexural strength but little on the compressive itrength and fractule toughness. And also, considering the distributions of steel fiber, workablity and the maxinium size of coarse dqgregates, the optimum content of steel fiber seemed to be about 1.0 '0, and when lts length uias longer the results were somewhat tavorable.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.568-574
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• 2001

From measured responses of concrete three-point bend tests, the average values of the responses have been calculated. The fracture behavior of continuously propagating concrete crack has been analyzed from the average responses. The experimental parameters of this study were the initial notch sizes of 25.4㎜ and 6.4 ㎜ and the processing times of 2,000 sec. and 20 sec . The different notch sizes were used for the effects of the size of fracture process zone and specimen geometry, and the processing times for those of initial creep. However the load-point displacement rate in this study did not affect the experimental responses seriously. The average loads were calculated from the average external work of a series of tests, and average crack lengths were determined by using strain gages. Before the peak load, the resistance curve could be determined from the size of fracture process zone, but unstable crack propagation of 88㎜ occurred at the load-point displacement of 0.088∼0.154㎜ after the peak load. The average fracture energy density G$\_$F/$\^$ave/ = 115 N/m occurred during the unstable crack propagation. The fracture process zones were fully developed at the crack length of 111㎜, and the sizes of fracture process zone for initial notches of 25.4㎜ and 6.4㎜ were 86㎜ and 105㎜, respectively. Average fracture energy densities of the resistance curves after full development of fracture process zone were 229 N/m for the initial notch of 25.4㎜ and 284 N/m for 6.4㎜. The values were more than twice of G$\_$F/$\^$ave/.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.4
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• pp.300-306
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• 2002

In this paper the failure mechanisms and Charpy impact tests of carbon fiber polypropylene composites have been studied in the temperature range -5$0^{\circ}C$ to 6$0^{\circ}C$ and 3 different supported length of specimen (span length). There are significant effects of temperature and span length on impact fracture toughness, which shows a peak at ambient temperature and decrease as temperature is reduced. Fracture toughness shows a maximum at span length s=20mm. Failure mechanisms are characterized based on SEM examination, which is correlated the measured fracture toughness. Mafor mechansms of this composites can be classified as fiber matrix debonding, delamination, fiber pull-out and matrix deformation.

• Computational Structural Engineering
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• v.11 no.4
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• pp.383-390
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• 1998

0.93m/sec의 평균속도는 변위제어 삼점휨 실험된 콘크리트 보의 하중-변위 측정결과를 선형탄성파괴역학모델과 가상균열모델에 기초한 유한요소법으로 분석하였다. 두 모델 모두 실험결과와 잘 일치하며, 균열성장길이가 약 60∼70㎜가 될 때까지 안전된 균열성장을 보이다 불안정한 균열성장에 의해 파손되었다. 선형탄성파괴역학모델에 의한 수치해석 결과 에너지해방률은 균열성장길이에 비례해서 증가하였으며, 최대값(202N/m)에 이르게 되면 일정한 값을 유지하였다. 가상균열모델에 기초한 수치해석결과 이 연구에 사용된 하중속도와 시험편의 크기에 대해 70㎜의 완전한 파괴진행대가 평성되었으며, 이는 기존의 정적 실험결과에 대한 수치해석 결과보다 상당히 작은 값이었다.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.645-652
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• 2002

This paper presents the flexural behavior and strengthening effect of reinforced concrete beams bonded with carbon FRP plate. Parameters involved in this experimental study were plate bond length and sheet web anchorage length. Test beams were strengthened with FRP plate on the soffit and anchored with FRP sheet on the web. In general, strengthened beams with no web anchorage were failed by concrete cover failure along the longitudinal reinforcement. On the other hand, strengthened beams with web anchorage were finally failed by delamination shear failure within concrete after breaking of CFRP sheet wrapping around web. The ultimate load and deflection of strengthened beams increased with an increased bond length of FRP plate. Also, the ultimate load and deflection increased with an increased anchorage length of FRP sheet. Particularly, the strengthened beams with web anchorage maintained high ultimate load resisting capacity until very large deflection. The shape of strain distribution of CFRP plate along beam was very similar to that of bending moment diagram. Therefore, an assumption of constant shear stress in shear span could be possible in the analysis of delamination shear stress of concrete. In the case of full bond length, the ultimate resisting shear stress provided by concrete and FRP sheet Increased with an increase of web anchorage length. In the resisting shear force, a portion of the shear force was provided by FRP anchorage sheet.