• Composites Research
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• v.37 no.3
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• pp.190-196
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• 2024

The bipolar plate is a crucial element of the vanadium redox flow battery (VRFB) as it serves as both the electrical conduit and the structural support for the cell within the VRFB stack. Although, the graphite material is primarily used for the bipolar plate due to its excellent electrical conductivity, a significant limitation of performance of the VRFB is present due to high interfacial contact resistance (ICR) arises between the electrode and bipolar plate in the cell stack. This study aims to develop an integrated electrode-bipolar plate assembly that will address the limitations of the ICR. The integrated assembly was constructed using a single carbon felt with thermoplastic and thermoset polymers utilizing hot press method. Experimental results verify that the bipolar plate assembly exhibits reduced area specific resistance (ASR) due to the continuous electrical path. Additionally, from the charge/discharge cell test results, the integrated assembly shows improved cell performance. Therefore, the developed integrated electrode-bipolar plate assembly can serve as a substitute for the conventional bipolar plate and electrode assembly.

• Journal of Adhesion and Interface
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• v.22 no.2
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• pp.63-68
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• 2021

Unsaturated Polyester Resin (UPR) is in general used as a resin to prepare for composite materials with reinforcing materials such as glass fibers. UPR, a thermosetting resin, is used in industry to prepare for sheet molding compound (SMC) molding prepreg that has excellent productivity and is advantageous for mass production among various molding methods of composite materials. The fiber-reinforced composite material using UPR as a matrix material is light and has the advantage of excellent physical properties, but it is weak against impact and is fragile. Four types of polyurethane were synthesized and added to UPR resin to overcome the shortcomings.

• Composites Research
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• v.33 no.2
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• pp.55-60
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• 2020

A study on the heating behavior and adhesion property of structural epoxy adhesive through induction heating have been conducted. An adhesive for induction heating was manufactured through mixing with nano and micro sized Fe₃O₄. From the results, it was observed that induction heating is less affected by adherend (GFRP) thickness than oven heating. The heating rate of Fe₃O₄ embedded epoxy adhesive using induction heating much higher than that of oven curing process and it is more appreciable when the contents of Fe₃O₄ increased. Furthermore, adhesion strength increased with increase of Fe₃O₄ particle contents.

• Composites Research
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• v.31 no.4
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• pp.122-127
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• 2018

Sandwich composites of carbon fiber reinforced plastic(CFRP) and polymer foam will be used to automobile and aerospace industry according to increasing importance of light weight. In this study, mechanical and heat resistance properties of sandwich composites were compared with type of polymer foam (polyethylene terephthalate(PET), polyvinylchloride(PVC), epoxy and polyurethane). All types of polymer foams were degraded to 30, 60, 120, 180 minutes in $180^{\circ}C$. After heat degradation, the polymer foams were observed using optical microscope and compressive test was performed using universal testing machine(UTM). Epoxy foam had the highest compressive property to 2.6 MPa and after thermal degradation, the mechanical property and structure of foam were less changed than others. Epoxy foam had better mechanical properties than other polymer foams under high temperature. Because the epoxy foam was post cured under high temperature. As the results, Epoxy foam was optimal materials to apply to structures that thermal energy was loaded constantly.

• Composites Research
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• v.16 no.4
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• pp.51-58
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• 2003

Since the reliability of adhesively bonded joints is much dependent on the curing status of thermosetting adhesive, the on-line cure monitoring during the cure of adhesively joints could improve the quality of adhesively bonded joints. In this work, the dielectric method which measures the dissipation factor of the adhesive during the cure of joints and converts it into the degree of cure of the adhesive was devised. The relation between the dissipation factor and the degree of cure of adhesive was investigated, which could eliminate the temperature effect on the dissipation factor that is a strong function of the degree of cure and temperature of adhesive. From the investigation, it was found that the dissipation factor showed a trend similar to the cure rate of the adhesive.

• Polymer(Korea)
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• v.25 no.1
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• pp.71-77
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• 2001

Unsaturated polyester(UP) resin is one of the major thermosetting resins. It is very useful as the matrix resin of the composite material because of its low viscosity. The polymer resin, however, has several drawbacks; The volume shrinkage occurs during the crosslinking reaction of the UP resin with styrene monomer and the resulting polymer is weak to the alkali and also brittle. The mechanical properties of UP resin can be improved by blending various materials. In this study, polyurethane(PU) was used as a modifier in order to enhance the toughness of the UP resin. The goal of the research is to study the effect of the polyol molecular weight as a PU soft segment and the PU contents on the toughness of PU-modified UP resins. UP/PU polymer network may occur through the reaction between isocyanate group in the methyldiisocyanate(MDI) and hydroxyl group in the UP molecules. The maximum toughness value was shown at 2 wt% of the PU content. This effect results from the incorporation of the PU segment into the UP resin.

• Journal of Aerospace System Engineering
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• v.16 no.1
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• pp.12-16
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• 2022

Currently, Induction welding is attracting attention as a non-contact, clean and fast welding process. However, since thermoplastic resins are not affected by electromagnetic fields, induction welding requires a heating element called a susceptor. Researches are being conducted with the aim of achieving high-quality bonding, however, the factor of a heating element is an issue, hence the need to set a standard. Specimen fabrication and testing are conducted according to ASTM D5868. In this study, we propose that the evaluation criteria be judged on the basis of three factors; the condition of the welded joint surface, void content, and lap shear strength. Since the adhesive surface to be welded melts and solidifies as it cools, rapid temperature changes can generate pores. In addition, if the heating is not uniform, it is difficult to expect the desire performance. Using PA6 (CF 30%) thermoplastic, susceptor fabrication, induction welding and performance verification were conducted.

• Composites Research
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• v.35 no.2
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• pp.53-60
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• 2022

This study uses Diglycidyl ether of terephthalylidene-bis-(4-amino-3-methylphenol) (DGETAM), an amine hardener 4,4'-diaminodiphenylethane (DDE) and cationic catalyst N-benzylpyrazinium hexafluoroantimonate (BPH) to make epoxy film. For analysis, ¹H_NMR and FT-IR were used to verify proper synthesis, and the liquid crystallinity of DGETAM was checked using Differntial Scanning Calorimetry and Polarized Optical Microscopy. Thermal conductivity of the sample was measured using Laser Flash Apparatus. Thermal stability as well as thermal conductivity is important when used as a packaging material. Activated energy is the energy needed to generate a response, which can be used to estimate the energy required to maintain physical properties. It was obtained using the Arrhenius equation based on the data measured by isothermal decomposition using Thermogravimetric Analysis. Measurement of the thermal conductivity of epoxy films showed higher thermal conductivity when DDE was used, and it was found that thermal conductivity had an effect on thermal stability, given that it represented an activation energy similar to a film with BPH upon 5% decomposition.

• Composites Research
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• v.34 no.3
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• pp.192-198
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• 2021

Due to enormous market growing of electric vehicles without combustion engine, reducing unwanted BSR (buzz, squeak, and rattle) noise is highly demanded for vehicle quality and performance. Particularly, innerbelt weatherstrips which not only block wind noise, rain, and dust from outside, but also reduce noise and vibration of door glass and vehicle are required to exhibit high damping properties for improved BSR performance of the vehicle. Thermoplastic elastomers (TPEs), which can be recycled and have lighter weight than thermoset elastomers, are receiving much attention for weatherstrip material, but TPEs exhibit low material damping and compression set causing frictional noise and vibration between the door glass and the weatherstrip. In this study, high damping EPDM (ethylene-propylene-diene monomer)/PP (polypropylene) thermoplastic vulcanizates (TPV) were investigated by varying EPDM/PP ratio and ENB (ethylidene norbornene) fraction in EPDM. Viscoelastic properties of TPV materials were characterized by assuming that the material damping is directly related to the viscoelasticity. The optimum material damping factor (tanδ peak 0.611) was achieved with low PP ratio (14 wt%) and high ENB fraction (8.9 wt%), which was increased by 140% compared to the reference (tanδ 0.254). The improved damping is believed due to high fraction of flexible EPDM chains and higher interfacial slippage area of EPDM particles generated by increasing ENB fraction in EPDM. The stick-slip test was conducted to characterize frictional noise and vibration of the TPV weatherstrip. With improved TPV material damping, the acceleration peak of frictional vibration decreased by about 57.9%. This finding can not only improve BSR performance of electric vehicles by designing material damping of weatherstrips but also contribute to various structural applications such as urban air mobility or aircrafts, which require lightweight and high damping properties.

• Composites Research
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• v.29 no.6
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• pp.408-413
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• 2016

Commonly-used polymers are manufactured as versatile forms. Furthermore, continuous polymer fibers are recently manufactured using nylon or aramid fiber. One of common epoxy was also used to make polymer fibers. Bisphenol-A type was used as base epoxy whereas amine and anhydride were used as hardeners. Epoxy fibers was cured by stepping up the temperature to maintain the shape of epoxy fiber. Surface energy was measured to confirm the degree of interfacial adhesion by modified static contact angle method. After mechanical properties were measured via fiber tensile test, the evaluation of fiber fracture was proceeded. Tensile strength of epoxy fiber using amine type hardener was higher as 138 MPa than anhydride case as 70 MPa. Fractured surface exhibited different failure patterns at the cross-section.