• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.997-1002
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• 2001

Tensile strength of CFRP (Carbon Fiber Reinforced Polymer) is approximately 10 times higher than that steel reinforcement, but the design strength of CFRP is normally reduced by the bond failure between RC and CFRP. Many researches have been carried out, concerned with bond behavior between RC and CFRP to prevent the unpredicted bond failure of RC beam strengthened by CFRP, but the national design code for design bond strength of CFRP hasn't been constructed. In this study, 3 beams specimen strengthened by CFRP under the variable of bonded length were tested to derive the design bond strength of CFRP to the RC flexural members. Also 2 beams specimen strengthened by CFRP were tested to inspect the construction environment effects such as mixing error of epoxy resin and the amount of primer epoxy resin. From the test results, It is concluded that the maximum design bond strength of CFRP to RC flexural member is considered to be $\tau_{a}$=8kgf/$cm^{2}$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.422-425
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• 2005

In an transversely isotropic composite laminates, the velocities, the particle directions and the amplitudes of reflected and transmitted waves were obtained using the equation of motion, the constitutive equation, and the displacement equation expressed by wave number and frequency Eigenvalue problem involving a velocity was solved by Snell's law. Finally, the results were confirmed by T300 Carbon fiber/5208 Epoxy materials. This approach could be applied to the detection of flaws in a transversely isotropic composite laminates by the water immersion C-scan procedure.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.43-47
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• 2002

Weight loss experiments have been performed for unidirectional carbon fiber/epoxy laminates under both isothermal and cyclic thermal conditions. It was found that weight losses were the result of both specimen-geometry dependent oxidative degradation and volumetric geometry dependent thermal degradation. Thermal degradation was found to play a major role in the overall weight loss process, and photomicrographs of cross-sectioned, aged specimens confirmed this fact. A method to predict the effect of isothermal environment on the weight loss was introduced and found to be in good agreement with experimental data at temperatures near Tg (glass transition temperature).

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1773-1782
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• 1994

In this paper, the expert cure system for carbon fiber epoxy composite materials, which controls the temperature and pressure of the autoclave according to the several rules, was developed to manufacture better composite products in shorter curing time. The rules were based on the on-line measured quantities such as the dielectric properties and temperature of the composites and the pressure of the autoclave. The curing time and the mechanical properties of the composite materials manufactured with the expert cure system were compared to those of the specimens manufactured with the conventional cure cycle.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.441-446
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• 2000

Although the net-shape molding of composites is generally recommended, molded composites frequently required cutting or grinding due to the dimensional inaccuracy for precision machine elements. During the composite machining operations such as cutting and grinding, the temperature at the grinding area may increase beyond the allowed limit due to the low thermal conductivity of composites, which might degrade the matrix of composite. Therefore, in this work, the temperature at the grinding point during surface grinding of carbon fiber epoxy composite was measured. The grinding temperature and surface roughness were also measured to investigate the surface grinding characteristics of the composited. The experiments were performed both under dry and wet grinding conditions with respect to cutting speed, feed speed, depth of cut and stacking angle. From the experimental investigation, the optimal conditions for the composite plain grinding were suggested.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.10
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• pp.113-120
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• 1995

여러가지 두꺼운 복합재료 구조물은 3차원 압축 부하 상태에 노출되는 경우가 발생한다. 이런 경우에 있어 서의 복합재료 압축 강도는 압축 평균 응력을 이용하면 예측이 가능할지도 모른다. 이번 연구 에서는 압축 평균 응력을 이용하여 탄소섬유 강화 복합재료들의 압축 강도를 예측하는 모델을 개발 하고자 한다. 이 모델은 압축강도에 영향을 주는 요소, 초기 misalignment를 고려하였고, 탄소섬유와 수지사이에 접합강도가 임계값을 초과할때 복합재료의 파괴가 일어난다고 가정한다. 또 여라가지 문헌들을 통하여 유압이 접합강도에 미치는 점들을 보여준다. 본 모델을 이용한 예측값들은 가해지는 유압에 따라 증가되며, 실험값들과 비교 분석될 것이다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2154-2164
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• 1995

In this study, a dielectric cure monitoring system which consists of an electric circuit, a sensor and a personal computer was developed to on-line monitor the dielectric properties of carbon fiber epoxy composite materials. Also, the kinetic model of carbon fiber epoxy composite materials was developed by curve fitting of differential scanning calorimetry data. The start and end points of cure and the relationship between the dissipation factor and the degree of cure were obtained by comparing the dissipation factor from the dielectric properties with the degree of cure from the DSC data. The relationship between the dissipation factor and the degree of cure was tested under various temperature profiles.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.2
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• pp.62-69
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• 2006

In transversely isotropic composite laminates, the velocities, the particle directions and the amplitudes of reflected and transmitted waves were obtained using the equation of motion, the constitutive equation, and the displacement equation expressed by wave number and frequency. Eigenvalue problem involving a velocity was solved by Snell's law. Finally, the results were confirmed by 7300 Carbon fiber/5208 Epoxy materials. This approach could be applied to the detection of flaws in transversely isotropic composite laminates by the water immersion C-scan procedure.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.6
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• pp.65-70
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• 2000

Although the net-shape molding of composites is generally recommended, molded composites frequently requires cutting or grinding due to the dimensional inaccuracy for precision machine elements. During the composite machining operations such as cutting and grinding, the temperature at the grinding area may increase beyond the allowed limit due to the low thermal conductivity of composites, which might degrade the matrix of composite. Therefore, in this work, the temperature at the grinding point during surface grinding of carbon fiber epoxy composite was measured. The grinding temperature and surface roughness were also measured to investigate the surface grinding characteristics of the composites. The experiments were performed both under dry and wet grinding conditions with respect to cutting speed, feed speed, depth of cut and stacking angle. From the experimental investigation, the optimal conditions for the composite surface grinding were suggested.

• The Korean Journal of Rheology
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• v.10 no.2
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• pp.106-112
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• 1998

항공기용 소재로 개발된 에폭시/탄소섬유 복합재료가 매트릭스의 유리전이온도에 육 박하는 온도주기를 경험할 때 발생하는 복합재료의 구조 및 물성변화를 실험과 모델링을 통 하여 연구하였다. 복합재료의 표준 경화온도인 177$^{\circ}C$에서 2시간 체류시킨후 냉각시키는 바 복 열주기는 복합재료를 취약하게 하여 결국 표면에서부터 미세크랙이발생한다는 것을 알수 있었다. 이러한 열주기에 따른 미세크랙 현상은 매트릭스의 분해반응이 발생할수 있는 유효 표면적을 증가시키고 크랙을 통하여 산소의투과를 용이하게 함으로서 산화반응을 가속화하 여 복합재료시편의 무게감소를 가속화시키는 것으로 판단된다. 특히 본 연구에서는 등온과 등속도 승온조건을 주기적으로 반복하는 열주기 조건을 해석하기 위하여 열주기 조건을 특 정온도에서의 등오시간으로 전환할 수 있는 e-quivalent cycle time(ECT)를 제안하였고 이 를 이용하여 열주기에 의한 복합재료 손상의 가속/감속 현상을 규명할수있었다.