• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.20-25
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• 2000

In order to study the impact fracture behavior of brittle materials, a steel-ball-impact experiment was Performed. Five kinds of materials were used in this study : soda-lime glass plates, glass/epoxy prepreg-one layer-bonded and unbonded glass plates, glass/epoxy prepreg-three layers-bonded and unbonded glass plates. Fracture patterns, the maximum stress and absorbed fracture energy were observed according to various impact velocities 40-120m/s. With increasing impact velocity, ring crack, cone crack, radial crack and lateral crack took place in the interior of glass plates. The generation of such cracks was largely reduced with glass/epoxy prepreg coating. Consequently, it is thought that the characteristics of the dynamic Impact fracture behavior could be evaluated using the absorbed fracture energy and the maximum stress measured at the back surface of glass plates.

• Polymer(Korea)
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• v.24 no.3
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• pp.350-357
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• 2000

Curing behaviors of glass/epoxy prepreg for printed circuit boards (PCB) were studied by using dielectrometer and differential scanning calorimeter. This prepreg was showed the lowest ionic viscosity at about 115$^{\circ}C$, and then the ionic viscosity was gradully increased up to 15$0^{\circ}C$. This indicated that the curing reaction of this prepreg started at 115$^{\circ}C$ and the molecular weight was increased by the accelerated thermal cross-linking reaction. The loss factor and tan $\delta$ values were also measured and discussed. The dielectric behaviors of this prepreg system were also measured according to the cure cycle for PCB. This material was found to be thermally stable up to about 30$0^{\circ}C$ and then was showed an abrupt decomposition beyond this temperature.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.48-56
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• 1997

This work has been investigated in order to study the influence of the moisture absorption on the mechanical pf the glass fiber/epoxy resein composites and the carbon fiber/epoxy resein composites. The types of glass fiber used in the glass fiber/epoxy resein composites were randomly oriented fiber and plain fabric fiber. And carbon fiber.epoxy resein composites was laminated with fabric prepreg which was formed with carbon fiber and epoxy resein. Both composites were immersed up to 100 days in distilled water at $80^{\circ}C$, and then dried up to 3 days in an oven at 80$80^{\circ}C$. Both composites were measured for the weight gain of water(wt.%) and tensile strength through immersion and dry time. Consequently, it was found that the tensile strength of thw glass fiber/epoxy resein composites and the carbon fiber/epoxy resein composites were reduced proportionally to the moisture absortion rate. Also, the tensile strength of glass fiber composites was decreased more than that of the carbon fiber composites. Additionally, it was found that the tensile strength of all composites which decreased by moisture absorption were partly recovered by drying in an oven at 80$80^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.296-302
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• 2010

If the fiber reinforced plastic is exposed to the moisture for a long period of time, most of moisture absorption occurs on the resin place, thus dropping cohesiveness between the molecules as the water molecules permeated between high molecular chains grant high molecular mobility and flexibility. Also as the micro crack occurs due to the permeation of moisture on the interface of glass fiber and epoxy resin, it is developed to the overall damage of interface place. Hence, the study on absorption is essential as the mechanical and physical properties of fiber reinforced composites are reduced. However, the study on absorption has the inconvenience needing to expose composite materials to fresh water or seawater for 1 month or up to 1 year. Therefore, this study has exposed fiber reinforced composites to fresh water and has developed a model with an accuracy of 98% after comparing the analysis value obtained by using ANSYS while basing on the experimental value of property decline by absorption and the basic properties of glass fiber and epoxy resin used in the experiment.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.53-58
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• 2000

During the curing process of thick glass/epoxy laminates, a substantial amount of temperature lag and overshoot at the center of the laminates is usually experienced due to the large thickness and low thermal conductivity of the glass/epoxy composites. Also, it requires a longer time for full and uniform consolidation. In this work, temperature, degree of cure and consolidation of a 20mm thick unidirectional glass/epoxy laminate were investigated using an experiment and a 3-dimentional numerical analysis considering the exothermic reaction. From the experimental and numerical results, it was found that the experimentally obtained temperature profile agreed well with the numerical one and the cure cycle recommended by the prepreg manufacturer should be modified to prevent a temperature overshoot and to obtain full consolidation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2853-2865
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• 2000

During the curing process of thick glass/epoxy laminates, a substantial amount of temperature lag and overshoot at the center of the laminates is usually experienced due to the large thickness and low thermal conductivity of the glass/epoxy composites. Also, it takes a longer time for full and uniform consolidation. In this work, temperature, degree of cure and consolidation of a 20 mm thick unidirectional glass/epoxy laminate were investigated using an experiment and a 3-dimentional numerical analysis. From the experimental and numerical results, it was found that the experimentally obtained temperature profile agreed well with the numerical one, and the cure cycle recommended by the prepreg manufacturer should be modified to prevent a temperature overshoot and to obtain full consolidation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1514-1519
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• 2001

This paper is concerned with design, manufacturing and performance test of LIPCA ( Lightweight Piezo- composite Curved Actuator) using a top carbon fiber composite layer with near -zero CTE(coefficient of thermal expansion), a middle PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by thigh tweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 $^{circ}C$ after following an autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detached from a flat mold. The analysis method of the cure curvature of LIPCA using the classical lamination theory is presented. The predicted curvatures are fairly in agreement with the experimental ones. In order to investigate the merits of LIPCA, a performance test of both LIPCA and THUNDE$^{TM}$ were conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDERT$^{TM}$.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.557-563
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• 2010

Mode II interlaminar fracture toughness was measured and fractured surfaces were observed of carbon/epoxy and glass/epoxy woven fabric composites for carbody structure. Woven fabric carbon/epoxy and glass/epoxy composites that made with prepreg and epoxy resin(RS1222) are used in carbody structure of Korean tilting train(TTX) and low floor bus. ENF(End Notched Flexure) specimens having $120mm{\times}20m{\times}5mm$ shape and 35mm initial crack were made with each composites and three point bending tests according to ASTM D790 were conducted for these specimens. Crack lengths in tests were recorded using optical microscope and digital camcorder. NL(Non Linear), 5% offset and Max. load points in load -displacement curves were checked and mode II interlaminar fracture toughness of these points were calculated and compared. Fractured surfaces of specimens were observed using optical microscope and mode II delamination behavior of each composites was discussed.

• Fire Science and Engineering
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• v.16 no.4
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• pp.65-71
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• 2002

In this paper, the thermal and flame properties of GFRP with various flame retardant(aluminum trihydrate, antimony trioxide) compositions have been investigated by thermal analysis and flammability tests(LOI test, flammability 45 degree test). The flame and mechanical properties(hardness, tensile strength, modulus) of general purpose grade glass fiber/unsaturated polyester composite with flame retardant composition have been also evaluated. The effect of cure pressure on the flame properties of aerospace grade glass fiber/epoxy composite was investigated. Considering the flame and mechanical property of composite, we could determine the optimum flame retardant composition(ATH 10∼20 phr). Test results show that the flame property of glass fiber/epoxy composite is considerably affected by cure pressure conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.9
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• pp.788-795
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• 2008

To understand the tensile behaviors of GFRP at low temperature, three types of specimen have been used in this study. Tensile properties and fracture mechanisms for three orthogonal orientations of plain weave glass fabric reinforced epoxy resin laminate were investigated at temperature range of about -30 to $15^{\circ}C$. The tensile properties of axial and edge type specimen decrease slightly with decreasing temperature to $-20^{\circ}C$. However, at $-30^{\circ}C$ the decreases in the tensile properties increased considerably. Below $-20^{\circ}C$, thickness type specimen showed a marked decreases in the tensile properties. It was obvious that the fracture manner of thickness type specimen was adhesive failure at above $-10^{\circ}C$ and a mixed adhesive and cohesive failure at below $-20^{\circ}C$.