• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.1
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• pp.115-126
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• 2001

In this paper, through a series of comparative experiments, effects of two different cure processing methods, cocure and precure, on the mechanical properties of honeycomb core materials for aircraft applications are considered. Mass of moisture accumulated into the closed cells of the sandwich panel specimen from the measured mass of moisture diffused to the full saturation state into the elements(skin, adhesive layer, Nomex honeycomb), consisting the honeycomb sandwich specimen has been calculated. Water reservoir of 70$\^{C}$ was used to have specimens absorb moisture to see the influence of moisture absorbed into sandwich panel on its mechanical properties. For the repair condition holding for 2 hours at 177$\^{C}$(350℉) temperature, a pressure due to the vapor expansion in each cell of the sandwich panel, which may result in the local separation of the interface between laminated skin and the surface of the honeycomb, has been estimated by vapor pressure-temperature relation from the thermodynamic steam table and compared to the pressure from the ideal gas state equation. The bonding strengths of the laminated skins on the flat surface of the Nomex honeycomb have been compared by the flatwise tension test and climbing drum peel test performed at room temperature for dry, wet and wet-repair specimens, respectively.

• Science of Emotion and Sensibility
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• v.17 no.1
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• pp.93-104
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• 2014

This paper investigates the physical properties such as water absorption, drying and hygral expansion of moisture responded transformable fibers and their knitted fabrics including dyeing characteristics according to the different dyeing time and temperature. For this purpose, three kinds of covered filament yarn specimens using HEF and spandex as core and PET, aerocool as a covering filament were prepared. The knitted fabric specimens were made using three kinds yarn specimens and dyed with different dyeing temperature and time. The moisture absorption, drying and hygral expansion of three kinds of knitted fabric specimens were measured and discussed with yarn structure. The wearing performance of these knitted fabric specimens were also measured and discussed with yarn characteristics using FAST system. Finally, the dyeing characteristics such as dye affinity, color difference and color fastness to washing of these knitted fabric specimens were measured and discussed with different dyeing temperature and time for examining dyeing process performance of these moisture responded transformable knitted fabrics.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.994-996
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• 1999

Hygrothermal aging at the elevated temperature induces the long-term degradation of the epoxy resin. We investigated the effects of hydrothermal stress on the dielectric breakdown phenomena of epoxy composite filled with natural zeolite. The cured specimens absorbed the moisture in the autoclave at $120^{\circ}C$. $T_g$ of the deteriorated composite by moisture absorption decreased. The dielectric breakdown strength decreased with the moisture absorption cycle. It was concluded that the thermal stress and the high water-vapour-pressure deteriorated the natural zeolite filled epoxy resin system, consequently and the tree growth rate increased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.536-538
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• 2011

In this study, the moisture absorption behaviors of the CNT reinforced unsaturated polyester composites were investigated along with exposure temperature and time. The tensile properties of the specimens were evaluated to identify the effect of absorbed moisture on the mechanical properties. The exposure temperatures of $25^{\circ}C$ and $75^{\circ}C$ were considered and the exposure time up to 600 hours was applied. According to the results, moisture absorption rate was increased as CNT content and exposure temperature were increased. The rate of decrease in tensile strength of the CNT reinforced unsaturated polyester composites was reduced due to the reinforcing effect of CNT compared to the unsaturated polyester resin.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.1
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• pp.7-14
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• 2012

CFRP composite material has the superior specific strength and rigidity compared to metallic materials, and is widely adopted in the various fields. However, CFRP composite material has the weakness in hygrothermal and crash environment. Especially, moisture ingress into composite material under hygrothermal environment can change molecule arrangement and chemical properties. In addition, interface characteristics and material component properties can be degraded. A collapse experiment has been made to research the differences of absorbed energy and deformation mode between absorbed specimens of moisture and non-moisture. As a result of this study, the effect of moisture absorption and impact loads of about 30~50% reduction in strength are shown.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.656-661
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• 2013

In this study, the moisture content, charge discharge current, electrostatic capacity and dielectric loss tangent are measured for the specimen of bisphenol type epoxy resin which is mixed with squared amorphous silica filler and dipped in hot water of $50^{\circ}C$ for 169 days. The results of this study are listed below. The longer of deposition day, the charge and discharge current was increased. It is considered that the reason is because there was water attack through the squared silica surface. The longer of deposition day, the absorption rate of all specimens was increased. It found that the absorption rate reached saturated state after 100 days. The higher frequency and the longer of deposition day, the $tan{\delta}$ was decreased. Also, It found that the $tan{\delta}$ and electrostatic capacity of the specimen which is mixed with squared filler are greater.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.4
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• pp.402-410
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• 1996

Recently carbon fiber reinforced plastic(CFRP) has been used structural materials in corrosive environment such as for water, chemical tank and chemical pipes. However, mechanical properties of such materials may change when CFRP are exposed to corrosive environment for long periods of time. Therefore, it is important to understand the effect of moisture absorption on mechanical properties of the CFRP. In this study, degradation behavior of immersed carbon fiber/epoxy resin composite material was investigated using acoustic emission(AE) technique. Fracture toughness test are performed on the compact tension(CT) test specimens that are pilled by two types of laminates $[0^{\circ}_2$/$90^{\circ}_2]_3s$ and $[0^{\circ}_2$/$90^{\circ}_2]_6s$During the fracture toughness test, AE test was carried out to monitor the damage of CFRP by moisture absorption. In spite of the change of moisture absorption rate, the fracture toughness of CFRP was not change. As immersion time increased, AE event count numbers decreased in low amplitude range of AE for amplitude distribution histogram. The event in low amplitude range was known to be generated by debonding of matrix-fiber interface. Therefore, decrease of AE event count numbers in low amplitude range represents that debonding of matrix-fiber interface which was probably generated by moisture absorption.

• Journal of the Korean Wood Science and Technology
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• v.19 no.4
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• pp.52-61
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• 1991

In this paper, the difference of the property of absorption and desorption for five species in semi-steady state are studied. The species used are listed in Table 1 and the dimension of specimen was $8\times8{\times}T$(Tangential direction)cm and tested in various conditions. A change of average moisture content with time were measured in each cycles. The results obtained are summarized as follows. When the relative humidity in air was maximum or minimum, the distribution of moisture In wood of all specimens were illustrated by exponential curves of decrease or increased from lace 10 center of wood. From the consideration of coefficient of decrease(C), the amount of moisture change of spruce was larger than the others. The pheonomenon was considered no relation to the specific gravity in air dry, but the wood structures. The velocity of the absorption and desorption for species decreased in the order spruce(Picea sitchensis) neodobam(Fagus crenata), solsong(Tsuga heterophylla), meranti(Shorea sp.) and kaesoo(Cercidiphyllum japoicum). In case of constant temperature and water vapor pressure is changed. the amount of absorbed moisture was larger than that of constant water vapor pressure and temperature vaned. In this fact, it is considered that the property of sorption of wood is strongly influenced by vapor pressure gradient than temperature gradient.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.479-482
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• 1999

Cured epoxy resins are extensively used for the electrical insulation in high-voltage equipments. The bisphenol A-based epoxy resins lured with azine show, especially, good thermal properties and mechanical resistances. For the technical and economic reasons, varing amount of inorganic fillers are added to endow the required special properties. In the large generators and motors of power plants, epoxy insulation is disclosed to the harsh conditions like the superheated steam and abrupt temperature variation. Hygrothermal aging at elevated temperatures tends to induce degradation in epoxy resins. To predict the effect of this degradation in DGEBA/MDA/SN/zeolite system, we proceeded the forced moisture absorption experiment using the autoclave. The thermal properties of the untreated and treated specimens were analyzed by DSC and TGA under the nitrogen flowing condition. The moisture absorption results showed a weight increase during hygrothermal aging at 1207. At the initial aging period, the system leaded to more or less postcuring but more prolonged environmental aging leaded the discoloration of specimen and lowering the T$_{g}$./.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.529-531
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• 1999

In this Paper, the variable dielectric breakdown strengths of epoxy composites were investigated at belling absorption condition in order to observe the influences of moisture in out door use. Also. in order to improve withstand voltage properties at moisture absorbtion condition, IPN(interpenetrating polymer network) method was Introduced and the Influence was investigated. As Adding filler(SiO$_2$) classified by o(phr), 50(phr) and 100[phr] to two kinds of matrix resin, six kinds of specimens were manufactured. As a result, it was confirmed that dielectric breakdown strength wer degraded with boiling time and filer content increasing. But, it was confirmed that dielectric breakdown strength degrading rate were lowered by the Improvement of adhesion strength in IPN specimens.