• Composites Research
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• v.13 no.4
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• pp.54-66
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• 2000

Interfacial and microfailure properties of carbon fiber/epoxy matrix composites were evaluated using both tensile fragmentation and compressive Broutman tests with an aid of acoustic emission (AE) monitoring. A polymeric maleic anhydride coupling agent and a monomeric amino-silane coupling agent were used via the electrodeposition (ED) and the dipping applications, respectively. Both coupling agents exhibited significant improvements in interfacial shear strength (IFSS) compared to the untreated case under tensile and compressive tests. The typical microfailure modes including fiber break of cone-shape, matrix cracking, and partial interlayer failure were observed during tensile test, whereas the diagonal slippage in fiber ends was observed under compressive test. For both loading types, fiber breaks occurred around just before and after yielding point. In both the untreated and treated cases AE amplitudes were separately distributed for the tensile testing, whereas they were closely distributed for the compressive tests. It is because of the difference in failure energies of carbon fiber between tensile and compressive loading. The maximum AE voltage for the waveform of carbon or basalt fiber breakages under tensile tests exhibited much larger than those under compressive tests, which can provide the difference in the failure energy of the individual failure processes.

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.11a
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• pp.118-118
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• 1996

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.116-120
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• 2001

Fiber fracture is one of the dominant failure phenomena to determine total mechanical properties in composites. Fiber fracture locations were measured by optical microscopic method and acoustic emission (AE) as functions of matrix toughness and surface treatment by the electrodeposition (ED), and then two methods were compared. Two AE sensors were attached on the epoxy specimen and fiber fracture signals were detected with elapsed time. The interfacial shear stress (IFSS) was measured using tensile fragmentation test and AE system. In ED-treated case, the number of the fiber fracture measured by an optical method and AE was more than that of the untreated case. The signal number measured by AE were rather smaller than the number of fragments measured by optical method, since some fiber fracture signals were lost while AE detection. However, one-to-one correspondence between the x-position location by AE and real break positions by optical method was generally established well. The fiber break source location using AE can be a valuable method to measure IFSS for semi- or nontransparent matrix composites nondestructively (NDT).

• Polymer(Korea)
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• v.25 no.4
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• pp.512-520
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• 2001

One of the most important factors which affect the mechanical properties of fiber-reinforced composite materials is the interfacial shear strength (IFSS). The IFSS of glass fiber and polycarbonate (PC)/styrene-co-acrylonitrile (SAN) blend system has been measured by the single fiber fragmentation test (SFFT). SAN contents were varied up to 30 wt% and the IFSS increased with the SAN contents. Styrene-co-maleic anhydride (SMA) was used as the compatibilizer and the glass fiber was surface treated with organosilane coupling agents. Addition of small amount of SMA in PC/SAN blend improved the IFSS by chemical bonding between maleic anhydride and silanol. The optimum MA content was 0.4 wt% of total matrix contents. Also, IFSS was greatly affected by the miscibility condition of SAN/SMA blends, which depended on the copolymer composition of SAN and SMA. It was found out that, higher IFSS could be obtained when the SAN/SMA blend was in miscible pairs. In case of SAN/SMA miscible pairs, the IFSS depended on the MA content in total matrix, not on the MA content in SMA.

• Journal of Life Science
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• v.7 no.4
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• pp.329-335
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• 1997

This study was conducted to investigate the effect of dietary fiber(DF) levels on the meat quality in colored broiler. Colored broiler were fed on containing corn-soy basal diet(DF 5%) and high level(DF 6,7 and 8%) of dietary fiber diets for 7 weeks. Dietary fiber level of diet was make up by adding some alffalfa meal. Colored broiler meats were stored at 3$\circ$ for 24hr after skaughter, and used to analyze physico-chemical properties. Proximate component, pH, shear force value, myofibril fragmentation index, water holding capacity, cooking loss, protein extractability, fatty acid composition, Hunter's L, a value and palatability of cooked meat were not significantly affected by dietary fiber levels, whereas the Hunter's value of meat was significantly affected bty dietary fiber levels for the final period of feeding. Crude protein content, myofibril fragmentation index, water holding capacity, protein extractability and Hunter's b value of breast meat's were higher than thigh meat's, but crude fat content, pH, shear force value, cooking loss, palmitoleic acid, linolenic acid, and Hunter's a value were lower, regardless of dietary fiber level.

• Korean Journal of Materials Research
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• v.7 no.5
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• pp.434-443
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• 1997

유리섬유와 에폭시 수지와의 계면전단강도에 미치는 수분흡수, 섬유직경 및 섬유의표면상태 등의 영향을 검토하기 위해서 two fiber fragmentation 시험법을 사용하였다. 그리고 유리섬유/에폭시 수지의 일방향 복합재료에서 수분흡수가 복합재료의 기계적 성질에 미치는 영향에 대해서도 검토하였다. 그 결과, two fiber fragmentation시험에서 계면전단강도는 수분흡수량 및 섬유직경이 클수록 작게 나타났으며, sizing한 것이 desizing한 것보다 크게 나타났다. 또 수분흡습에 의해 감소되었던 계면전단강도는 건조에 의해서 처음의 값의 약 50-60%까지 회복됨을 나타내었다. 그리고 일방향 복합재료의 인장강도는 수분흡수량이 증가함에 따라 현저히 감소함을 보였다.

• Composites Research
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• v.25 no.6
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• pp.205-210
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• 2012

The single carbon fiber tensile test was performed with electrical resistance measurement. Tensile property of single carbon fiber which accompanied by the relationship between the electric resistance and the strain was investigated. Since the collected data showed a linear relationship between them, the coefficient of fiber slip ratio (FSR) was obtained by computation. The fragmentation specimen (FS) was tested under tensile loading, and the single carbon fiber broke first due to the stress transferring form matrix to reinforcing fiber. The stress distribution of carbon fiber could be observed via the electrical resistance change. Slipping between carbon fiber and matrix was predicted based on the fragmentation test results, and the FSR was used to evaluate interfacial adhesion comparatively. The large FSR indicated poor interfacial bonding. Work of adhesion between carbon fiber and matrix was measured to verify the FSR method, and two results exhibited a consistent conclusion.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.28-31
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• 1999

Carbon fiber/epoxy composites using electrodeposited monomeric and polymeric coupling agents were compared with the dipping and the untreated cases. Treating conditions such as time, concentration and temperature were optimized. Four-fibers embedded micro-composites were prepared for fragmentation test. Interfacial properties of four-fiber composites with different surface treatments were investigated with simultaneous acoustic emission (AE) monitoring. The microfailure mechanisms occurring from fiber break, matrix and interlayer crackings were examined by AE parameters and an optical microscope. It was found that interfacial shear strength (IFSS) of electrodeposited carbon fibers was much higher than the other cases under dry and wet conditions. Well separated and different-shaped AE groups occurs for the untreated and ED treated case, respectively.

• Composites Research
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• v.16 no.2
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• pp.68-73
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• 2003

Interfacial properties and electrical sensing fer fiber fracture in carbon and SiC fibers/epoxy composites were investigated by the electrical resistance measurement and fragmentation test. As fiber-embedded angle increased, the interfacial shear strength (IFSS) of two-type fiber composites decreased, and the elapsed time takes long until the infinity in electrical resistivity. The initial slope of electrical resistivity increased rapidly to the infinity at higher angle, whereas electrical resistivity increased gradually at small angle. Furthermore, both fiber composites with small embedded angle showed a fully-developed stress whitening pattern, whereas both composites with higher embedded angle exhibited a less developed stress whitening pattern. As embedded angle decreased, the gap between the fragments increased and the debonded length was wider for both fiber composites. Electro-micromechanical technique could be a feasible nondestructive evaluation to measure interfacial sensing properties depending on the fiber-embedded angle in conductive fiber reinforced composites.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.04a
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• pp.244-247
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• 1999