• Composites Research
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• v.32 no.5
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• pp.270-278
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• 2019

In this study, the transverse mechanical properties of the unidirectional fiber reinforced composite modeled with fiber, matrix, and interphase is predicted with the representative volume elements and is calibrated by adjusting the properties and thickness of the interphase by referring to the test results. While the conventional representative volume elements modeled with fiber and matrix shows high predictive accuracy for the longitudinal mechanical properties, but it shows some deviations in the transverse mechanical properties. In order to compensate such gaps, the interphase region is employed, and its mechanical properties are adjusted to improve the prediction accuracy according to various elastic modulus, thickness, and strength parameters. As a result, the deviation of the transverse elastic modulus and strength is reduced significantly similar to the test results of the unidirectional composites with the accuracy of the longitudinal mechanical properties preserved.

• Computational Structural Engineering
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• v.10 no.1
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• pp.129-134
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• 1997

Interfacial stress singularity in a unidirectional two-dimensional laminate model consisting of an elastic fiber and a viscoelastic matrix has been investigated using the time-domain boundary element method. First, the interfacial singular stresses between the fiber and the matrix of a unidirectional laminate subjected to a uniform transverse tensile strain have been investigated near the free surface, but without any defect or any edge crack. Such a stress singularity might lead to fiber-matrix debonding or interfacial edge cracks. Then, the overall stress intensity factor for the case of a small interfacial edge crack of length a has been computed.

• Polymer(Korea)
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• v.27 no.3
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• pp.189-194
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• 2003

Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermo setting composite with different curing processes were investigated using electro-micromechanical test. After curing, the residual stress was monitored by measurement of electrical resistance and then compared to various curing processes. In thermal curing case, matrix tensile strength, modulus and interfacial shear strength were higher than those of ultraviolet curing case. The shrinkage measured during thermal curing occurred significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient. The apparent modulus measured in the thermal curing indicated that mechanical and interfacial properties were highly improved. The reaching time to the same stress of thermal curing was faster than that of UV curing case.

• Journal of Adhesion and Interface
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• v.6 no.2
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• pp.13-20
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• 2005

Interfacial shear strength (IFSS) of environmentally friendly natural fiber reinforced polymer composites plays a very important role in controlling the overall mechanical performance. The IFSS of various Ramie and Kenaf fibers/epoxy composites was evaluated using the combination of micromechanical test and nondestructive acoustic emission (AE) to find out optimal conditions for desirable final performance. Dynamic contact angle was measured for Ramie and Kenaf fibers and correlated the wettability properties with interfacial adhesion. Mechanical properties of Ramie and Kenaf fibers were investigated using single-fiber tensile test and analyzed statistically by both uni-and bimodal Weibull distributions. An influence of clamping effect on a real elongation for both Ramie and Kenaf fibers were evaluated as well. Two different microfailure modes, axial debonding and fibril fracture coming from fiber bundles and single fiber composites (SFC) were observed under tension and compression.

• Elastomers and Composites
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• v.45 no.1
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• pp.2-6
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• 2010

The sizing treatments of PAN-based carbon fiber surfaces were carried out in order to improve the interfacial adhesion in the carbon fibers/nylon6 composite system. The parameter to characterize the wetting performance and surface free energy of the sized fibers were determined by a contact angle method. The mechanical interfacial properties of the composites were investigated using critical stress intensity factor ($K_{IC}$). The cross-section morphologies of sized CFs/nylon6composites were observed by SEM. As the experimental results, it was observed that silane-based sizing treated carbon fibers showed higher surface free energies than other sizing treatments. In particular, the KIC of the sizing-treated carbon fibers reinforced composites showed higher values than those of untreated carbon fibers-reinforced composites. This result indicated that the increase in the surface free energy of the fibers leads to the improvement of the mechanical interfacial properties of carbon fibers/nylon6 composites.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.4
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• pp.215-222
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• 2019

The heat conduction problem with discontinuous material coefficients generally consists of the conservative equation, boundary condition, and interface condition, which should be additionally satisfied in the solution procedure. This feature often makes the development of new numerical schemes difficult as it induces a layered singularity in the solution fields; thus, a special approximation is required to capture the singular behavior. In addition to the approximation, the construction of a total system of equations is challenging. In this study, a wedge function is devised for enriching the approximation, and the interface condition itself is embedded in the moving least squares(MLS) derivative approximation to consistently satisfy the interface condition. The heat conduction problem is then discretized in a strong form using the developed derivative approximation, which is named as the interface immersed MLS difference method. This method is able to efficiently provide a numerical solution for such interface problems avoiding both numerical quadrature as well as extra difference equations related to the interface condition enforcement. Numerical experiments proved that the developed numerical method was highly accurate and computationally efficient at solving the heat conduction problem with interfacial jump as well as the problem with a geometrically induced interfacial singularity.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.336-342
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• 1999

Various surface treatment techniques can be applied onto the surface of carbon fibers to increase interlaminar shear strength (ILSS). In a commerciaI treatment, first, surface of carbon fiber was oxidized, after that, a sizing agent was coated to improve handleability and adhesion to the matrix. Carbon fiber reinforced composites (CFRC) which is made of these fibers show excellent ILSS but show low vaIues of impact strength In this study, reactive and ductile interphase was introduced between fiber and matrix to increase both the ILSS and impact strength. By using electric conductivity of carbon fibers, flexible polymers which have ionizable group, i.e., MVEMA and EMA, were coated onto the surface (oxidized) of carbon fiber by the technique of electrodeposition. ILSS and impact strength of composites were evaluated according to the surface treatments, i.e., commercial sizing treatment, interphase introduction, and without sizing treatment. Izod impact strength and ILSS of CFRC were simultaneously improved in thc thickness range of $0.08{\sim}0.12{\mu}m$ of MVEMA interphase. Water resistance of the composites was decreased by introducing MVEMA interphase.

• Korean Journal of Materials Research
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• v.4 no.2
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• pp.127-135
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• 1994

We investigated the bonding interfaces of directly-bonded Si-Si and $Si-Sio_{2}$/Si wafer pairs. By the angle lapping-delineation, anisotropic etching, and (FIR)-TEM observation methods, we studied on the interface defects and the transient region originated from the interface stress, the various types of voids, the formation and stability of interfacial oxide. We also compared the interface image of the bonded $Si-Sio_{2}$ with that of a typically grown $Si-Sio_{2}$.

• Electrical & Electronic Materials
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• v.5 no.1
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• pp.81-88
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• 1992

본 연구는 고체-액체 계면에서 액체가 유동할때 발생되는 대전에 미치는 계면 활성제의 영향에 대하여 분석한 것이다. 유동전류는 유속의 증가에 따라 선형적으로 증가하고 유온의 증가에 따라 약 46[.deg.C] 이하에서는 증가하고 그 이상에서는 감소한다. 계면활성제의 종도가 증가함에 따라 유동전류는 감소하고 계면활성제의 한 분자내 산소 원자의 수가 많을수록 유동전류의 감소효과가 크게 됨을 제시할 수 있다. 계면활성제가 첨가된 절연유의 전도전류는 온도에 따라 무첨가보다 다소 큰 경향이 있으나 첨가량에는 현저한 차이가 없다.

• Korean Journal of Crystallography
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• v.9 no.2
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• pp.125-130
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• 1998

본 논문에서는 부직포를 삽입한 Gr/Ep 복합재료의 충격 흡수 특성을 연구하였다. 계면(interface) 층에 유리 부직포 또는 탄소 부직포를 삽입하여 복합적층판을 제작하였다. 저속충격 시험을 수행하였으며, 충격에 의한 층간분리(delamination)를 C-Scan과 현미경을 사용하여 관찰하였다. 실험결과 계면에 부직포를 삽입함으로써 충격에 의한 층간분리 면적이 감소함을 알 수 있었다.