• Korean Journal of Materials Research
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• v.5 no.2
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• pp.215-222
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• 1995

Anisotropic pitch-based C-type and hollow carbon fibers can obtain wider shear stresses during the spinning and induce higher molecular orientation than that of round along the fiber axis. These fibers reinforced unidirectional epoxy composites were prepared by hot-press moulding method and perpendicular and parallel thermal conductivities of the composites were measured by a steady-state meth od. In the case of round carbon fibers reinforced epoxy composites(H-CF/EP), thermal anisotropic factor showed nearly 50, while those of H-CF/EP and C-CF/EP showed about 130 and 118, respectively. As a result, both H-CF/EP and C-CF/EP had an excellent directional thermal conductivity to distribute heat, above 200 %.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.383-390
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• 2008

This paper presents the formulation and numerical implementation of a spectral scheme specially developed to simulate dynamic fracture events in unidirectional and cross-ply fiber-reinforced composites. The formulation is based on the spectral representation of the transversely isotropic elastodynamic relations between the traction stresses along the fracture plane and the resulting displacements. Example problem of dynamically propagating cracks in fiber-reinforced composites is investigated and compared with reference solutions available in the literature and/or experimental observations. This scheme can be directly applicable to the interfacial fracture analysis in the FRP reinforced concrete structures.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.1
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• pp.45-52
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• 1994

The study was conducted to evaluate reliability of the longitudinal tensile properties of unidirectional carbon fiber reinforced composites. Two kinds of carbon fiber reinforced composites laminates were tested in order to examine the factors of variability and have the information concerning reliability improvement. Temperature dependence of the strength and its variability were investigated by means of testing at two kinds of temperatures. Statistical distributions of the respective mechanical properties were obtained from the tensile tests. As a result, strength of composites was directly proportional to the ultimate strain and was not proportional to the elastic modulus. The fracture behavior in bending of notched plate was studied for a composite material. The uniform bending tests of notched plates have been carried out for a wide range of notch radii. The experiment shows that the nominal stress at failure decreased with decreasing notch radius and it approaches a constant value when the notch radius is less than about 0.3mm. The critical maximum stress is governed by notch root radius alone in the case of a constant thickness of specimen.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.406-412
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• 2015

Unidirectional carbon/carbon (C/C) composites were manufactured using phenolic resins as a precursor of the carbonized matrix throughout a one-step manufacturing process. Also, molybdenum oxide ($MoO_3$) and binder pitches were impregnated with phenolic resins to improve the bulk density and mechanical property of the C/C composites. In this study, the influence of $MoO_3$ and binder pitches on mechanical properties of the C/C composites were investigated by measuring flexural strength (${\sigma}_f$) and interlaminar shear strength (ILSS). The results show that the enhancement of interfacial adhesions between the fibers and matrix resins of the C/C composites with $MoO_3$ and binder pitches which led to the improvement of mechanical properties of the C/C composites. This indicates that the presence of $MoO_3$ and binder pitches in C/C composites can develop the graphite structure and increase the bulk density.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1990.11a
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• pp.63-68
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• 1990

Friction and wear behavior of a unidirectional high modulus carbon fiber reinforced epoxy composite exposed to high and low humidity was experimentally examined with various sliding speeds. The results show that the moisture at the sliding surface greatly influences friction and wear properties of the composite. It is also discoverd that the difference in friction and wear behavior between samples with different fiber orientations is mainly due to the anisotropic properties caused by the microstructure of oriented graphite crystals in the carbon fibers and the macrostructure of fiber orientation in the matrix.

• Tribology and Lubricants
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• v.6 no.2
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• pp.88-93
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• 1990

Friction and wear behavior of a unidirectional high modulus carbon fiber reinforced epoxy composite exposed to high and low humidity was experimentally examined with various sliding speeds. The results show that the moisture at the sliding surface greatly influences friction and wear properties of the composite. It is also discoverd that the difference in friction and wear behavior between samples with different fiber orientations is mainly due to the anisotropic properties caused by the microstructure of oriented graphite crystals in the carbon fibers and the macrostructure of fiber orientation in the matrix.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.1
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• pp.164-172
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• 1997

Two parameter technique that uses far-field stress and displacement distributions was applied to composite laminates in order to calculate mode II energy release rate, $G_{II}$ . The $G_{II}$ calculated by two parameter technique was compared with that calculated from the crack closure method to inspect the effectiveness of two parameter technique. Sensitivity study of two parameter technique to the crack extension size was also performed. The results showed that both methods produced comparable $G_{II}$ results. In particular, it was found that although the crack closure method was affected by the crack extension size, the two parameter technique was less affected by the crack extension size.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.183-186
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• 2001

In this paper, the analytical model to understand the propagation of electromagnetic waves in the foam core sandwich structures was proposed. Using the analytical model, efforts were made to find the optimal stacking sequence of composite skins for maximum transmittance of electromagnetic wave. Numerical analyses of unidirectional composites and foam as a function of incident angle were performed. From the results of analysis, the general tendencies of transmittance of electromagnetic wave through composites and foam were obtained. Based on the general tendencies, optimal stacking sequences of composite skins for the maximum transmittance of electromagnetic wave were found with certain ranges of incident angle using genetic algorithm(GA).

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.611-617
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• 1991

Effective stiffness of short fiber composite with a three-dimensional random orientation of fibers is derived theoretically and compared with available experimental data. The laminate analogy and transformed laminate analogy are used for modulus prediction of 2-D and 3-D random composites, respectively. The effective stiffness of random oriented fiber composite can be expressed in terms of longitudinal and transverse stiffnesses of unidirectional composites. The result of transformed laminate analogy is more accurate than other approaches such as, Christensen-Waals equational and Lavengood-Goettler equation, etc. Also the effective properties of random oriented fiber composite can be expressed in terms of fiber and matrix properties such as elastic modulus, shear modulus and Poisson's ratio.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.96-99
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• 2002

In order to determine the in-plane shear properties of unidirectional carbon fiber reinforced aluminum laminate composites, a new Iosipescu shear test fixture was developed, by using a fixture undergoing tensile force for the specimen edge to be subjected to compressive loads assumption, under plane stress. Also, to compare the results, Iosipescu shear test method by the modified Wyoming fixture and the off-axis tensile test were performed to determine the shear properties. Off-axis tension test was performed by using new oblique-shaped tabs proposed by Sun and Chung. [5] The oblique tabs reduced remarkably end-constraint effects of off-axis specimens with a aspect ratio of about eight. It is observed through the experimental results show that there is no significant difference between off-axis test results and those of Iosipescu shear test.