• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.1-6
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• 2007

The present study provides the compressive design allowable of a unidirectional glass/epoxy composite laminate processed by wet lay-up at room temperature. The compressive strength values measured from 39 specimens have been assumed to follow the two-parameter Weibull distribution. Following the statistical guidelines provided by MIL-HDBK-17F, the B-basis and A-basis values of the aforementioned laminate are found to be 82.6% and 65.9%, of the mean compressive strength, respectively. The B-basis value is then discounted further at 50% for the in-situ application on the main wing spar caps of an experimental canard aircraft.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.390-394
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• 2004

This is the study on dry sliding wear behavior of unidirectional carbon fiber reinforced epoxy matrix composite at ambient temperature. The wear rates and friction coefficients against the stainless steel counterpart specularly processed were experimentally determined and the resulting wear mechanisms were microscopically observed. Three principal sliding directions relative to the dominant fiber orientation in the composite were selected. Wren sliding took place against smooth and hard counterpart, the highest wear resistance and the lowest friction coefficient were observed in the antiparallel direction. When the velocity between the composite and the counterpart went up, the wear rate increased. The fiber destruction and cracking caused fiber bending on the contact surface, which was discovered to be dominant wear mechanism.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.234-237
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• 2001

In this study, efforts were made to understand the propagation of electromagnetic wave through the foam core sandwich structure by the analytical model. Foam core sandwich structure is composed of glass/epoxy composite skins and foam core. Transmittance and reflectance of the arbitrary linearly polarized incident TEM waves through the unidirectional composites, foam and foam core sandwich structures were determined as functions of thickness, fiber orientation of composites, incident angle and polarization angle by the analytical model. From the results of the analysis, the general tendency of transmittance and reflectance of electromagnetic wave through composites, foam and foam core sandwich structures was obtained.

• 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).

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.407-414
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• 2002

The knowledge of interaction of electromagnetic waves in composite structures is important for designing the shielding structure for antenna such as radome. Recently, radomes are constructed in the form of foam core sandwich structures that have many mechanical advantages such as high strength, long fatigue life, low density and adaptability to the intended function of structure. However, the propagation of electromagnetic waves is affected by high anisotropic permeability and loss tangent of the composite skin. In this study, the analytical model to understand the propagation of electromagnetic waves in the anisotropic composites and foam core sandwich structures with composite skins was proposed. Numerical analyses of unidirectional composites and foam core sandwich structure 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 core sandwich structure were obtained.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.9
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• pp.135-142
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• 1999

A constitutive model was proposed to study the effects of fiber waviness on the elastic properties of unidirectional composite materials. The predictions showed that the degree of fiber waviness significantly affected the elastic properties of composite materials. A special fabrication technique was developed for thic composite materials with various fiber waviness ratios. Tensile, compressive and flexural tests were conducted to obtain the elastic properties of composite materials with fiber waviness experimentally. The experimental result were in good agreement with the predictions.

• Steel and Composite Structures
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• v.21 no.6
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• pp.1211-1226
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• 2016

In this study, free vibration and damping characteristics of composite beams with holes are investigated, experimentally and numerically. Two types of samples with different fabrics are used: unidirectional and woven. The effects of diameter, number and location of circular holes on the vibration characteristics of composite beams are examined. The effects of rotation angle and minor to major diameter ratio of the elliptical hole are also investigated numerically. Moreover, the mode shapes of all types of beams are obtained numerically. According to the results, the natural frequency decreases with increasing hole diameter but increases very little with increasing the distance between the hole center and the clamped end. Damping ratio decreases by increasing the diameter of hole. But it fluctuates by increasing the diameters of holes of beam having three holes. Furthermore it decreases by increasing the distance between hole center and clamped end except for the range 50 mm to 100 mm.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.12
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• pp.130-138
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• 1995

Machined graphite/epoxy surfaces were studied by using SEM (Scanning Electron Microscopy), surface profilometry and its analysis to determine suitable surface describing parameters for machined unidirectional and multidirectional laminate composite. The surface roughness and profile are found to be highly depdndent on the fiber layup direction and the measurement direction. It was possible to machine 90 .deg. and -45 .deg. plies due to the adjacent plies, which were holding those plies. It was found that the microgeometrical variations in terms of roughness parameters $R_{a}$ without $D_{y}$(Maximum Damage Depth) region and $D_{y}$are better descriptors of the machined laminate composite surface than commonly used roughness parameters $R_{a}$and $R_{max}$ The characteristics of surface profiles in laminate composite are well represented in CPD (Cumulative Probability Distribution) plot and PPD (Percentage Probability Density) plot. Edge-trimmed multidirectional laminate surfaces are Gaussian and random for profiles measured along the tool movement direction, they are periodic and non-Gaussian in the direction perpendicular to the tool movement.t.ent.t.

• Computational Structural Engineering
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• v.9 no.1
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• pp.77-83
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• 1996

The overall stress intensity factor for edge crack located at the interface between fiber and matrix of a unidirectional graphite/epoxy laminate model subjected to a transverse tensile strain have been computed using the boundary element method. Such crack might be generated due to a stress singularity in the vicinity of the free surface. The amplitude of complex stress intensity factor has the constant value at large crack lengths.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.277-280
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• 2001

General source location method that use an arrival time differences among sensors is restricted to the composite material and the complex-shaped material. In this study, a bundle-type acoustic sensor composed of 6 pinducers was utilized to determine wave propagation direction and then to estimate source location of the unidirectional GFRP. For the purpose of the study, slowness curve for the material was obtained and made an assumption that the incident waves on pinducers are propagated as a plane wave. According to the results, measured propagation directions of the wave were coincide with theoretical background, however, it was a hassle to determine the source location exactly. But, it is expected that bundle-type sensor gives more accurate results for zone location than generally used acoustic sensors.