• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.76-79
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• 2000

Polymeric composites exhibit highly nonlinear and rate dependent behavior during loading and unloading in off-axis directions. The equilibrium state of stress during loading is lower than the state of stress produced at finite strain rates. The amount of stress relaxation during loading decreases. Interestingly, however, the stress goes up to reach to the equilibrium state of stress for a fixed displacement during unloading. The unloading behavior is quite similar to the loading behavior. The stress relaxation patterns during loading and unloading is also similar, and those depend on the fiber orientation angles and the loading and unloading rates. The AS4/PEEK thermoplastic composite is used to characterize the relaxation behavior for different off-axis angles and loading rates. There exists a transient loading region at the beginning of unloading. The effective stress and effective plastic strain concept is used to establish a master curve of stress recovery pattern for different off-axis angles and unloading rates.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.11-14
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• 2000

This paper presents the vibration control of a glass-fiber reinforced thermoplastic composite beam with a distributed PVDF sensor and piezo-ceramic achlator. The three types of different controllen which are PID, H$\infty$ , and p-synthesis ontrollcr are employed to achieve vibration suppression in the transient vibration of composite beam. In the H$\infty$ , controller design, 1st and 2nd natural frequencies are considered in the modeling, because robust control theory which has robustness to struchred uncertainty is adopled Lo suppress the vibration. If the controller designed by H$\infty$ , theory does not satisfy control performance, it is improved by $\mu$ -synthesis method with D-K iteration so that the$\mu$-contoller based on the structured singular value satisfies the nominal performance and robust performance Simulations and experiments were carried out with the designed controllers m order to demonstrate the suppression efficiency of each controller.

• Carbon letters
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• v.1 no.2
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• pp.87-90
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• 2000

Porous carbon from charcoal filled polypropylene composites were prepared and their mechanical properties were evaluated. In preparing the composites, crosslinking agent (sodium benzonate) were used in order to improve the bonding force between matrix and fillers. In this study, the effects of charcoal powder and sodium benzonate concentration on the mechanical properties and interface phenomena on the composites were evaluated. The mechanical properties of composites increased progressively with the decrease of filler loading. In the case of addition of the crosslinking agent into the composite, the mechanical properties were increased and showed maximum value at the 3 wt% concentration of sodium benzonate. According to the result of the TGA, the weight loss of composite according to crosslinking agent was not observed and initial thermal degradation temperature of composite reinforced charcoal was located at $390^{\circ}C$.

• Composites Research
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• v.28 no.4
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• pp.168-175
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• 2015

Recently, the applications of carbon fiber reinforced plastics (CFRPs) have become broader than ever when it comes to such industries as automotive, ships, aerospace and military because of their lightweight-ness and high mechanical properties. Thermosetting plastics like epoxy are frequently used as the binding matrix in CFRPs due to their high hardness, wetting characteristics and low viscosity. However, they cannot melted and remolded. For this reason, thermosetting plastic wastes have caused serious environmental problems with the production of fiber reinforced plastics. Thus, many studies have focused on the carbon fiber reinforced thermoplastics (CFRTPs) and recycling carbon fiber. In this study, recycled carbon fiber (RCF) was prepared from CFRPs using a pyrolysis method, which was employed to separate resin and carbon fiber. The degree of decomposition for epoxy resin was confirmed from thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The RCF was cut and ground to prepare a carbon fiber composite sheet (CFCS). CFCS was manufactured by applying recycled carbon fibers and various thermoplastic fibers. Various characterizations were performed, including morphological analyses of surface and cross-section, mechanical properties, and crystallization enthalpy of CFCS at different cooling conditions.

• Carbon letters
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• v.14 no.2
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• pp.76-88
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• 2013

Carbon fibers (CFs) have high service temperature, strength, and stiffness, and low weight. They are widely used as reinforcing materials in advanced polymer composites. The role of the polymer matrix in the composites is to provide bulk to the composite laminate and transfer load between the fibers. The interface between the CF and the resin matrix plays a critical role in controlling the overall properties of the composites. This paper aims to review the synthesis, properties, and applications of polymer matrices, such as thermosetting and thermoplastic resins.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.5
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• pp.173-178
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• 2001

This study investigates the effect of fiber content on the fracture behavior of thermoplastic composites (glass fiber/polypropylene). The fiber contents used were 20%, 30%, and 40% by weight. Fracture tests were performed using compact tension (CT) specimens made of composite sheets of three fiber contents (20%, 30%, 40%). The results showed that compliance, fracture load, and fracture toughness were affected by the fiber content. The compliance decreased with fiber content while the fracture load increased as the fiber content increased. The fracture toughness also increased as fiber content increased. Specifically, the fracture toughness increased 14% as the fiber content increased from 20% to 40%.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.91-96
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• 2000

Glass fiber reinforced thermoplastic composites were manufactured by Rapid Press Consolidation Technique(RPCT) as functions of temperature, pressure and time in pre-heating, consolidation and solidification sections during the manufacturing processing. It was found that the material property is greatly affected by pre-heating temperature under vacuum, mold temperature and molding pressure. Among them, the temperature In the mold was the most critical factor in determining the mechanical properties and the molded conditions of specimen. The crystallinity of PET matrix was also investigated by differential scanning calorimetry(DSC) measurements for various processing conditions. The level of crystallinity($X_c$) depended strongly on the mold temperature, cooling rate and the type of composite. The difference in $X_c$ is believed to be one of important factors in characterizing the mechanical properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.207-208
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• 2007

Recently, high performance microelectronic devices are designed in multi-layer structure in order to make dense wiring of metal conductors in compact size. Imprint lithography have received significant attention due to an alternative technology for photolithography on such devices. In this work, we synthesized dielectric composite materials based on epoxy resin, and investigated their thermal stabilities and dynamic mechanical properties for thermal imprint lithography. In order to enhance the mechanical properties and toughness of dielectric material, various modified polyetherimide(PEI) was applied in the resin system. Curing behaviours, thermal stabilities, and dynamic mechanical properties of the dielectric materials cured with various conditions were studied using dynamic differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and Universal Test Method (INSTRON).

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.326-330
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• 2004

Thermosetting matrix composites have disadvantages in terms of moulding time, repairability and manufacturing cost. Thus the high-performance thermoplastic composites to eliminate such disadvantages have been developed so far. As a result of environmental and economical concerns, there is a growing interest in the use of thermoplastic composites. However, since their mechanical properties are very sensitive to the environment such as moisture, temperature etc., those behaviors need to be studied. Particularly the temperature is a very important factor influencing the mechanical behavior of thermoplastic composites. The effect of temperature have not yet been fully quantified. Since engineering applications of reinforced composites necessitate their fracture mechanics characterization, work is in progress to investigate the fracture and related failure behavior. An approach which predicts the tensile strength was perpormed in the tensile test. The main goal of this work is to study the effect of temperature on the result of tensile test with respect to GF/PE composite. The tensile strength and failure mechanisms of GF/PE composites were investigated in the temperature range $60^{\circ}C\;to\;-50^{\circ}C$. The tensile strength increased as the fiber volume fraction ratio increased. The tensile strength showed the maximum at $-50^{\circ}C$, and it tended to decrease as the temperature increased from $-50^{\circ}C$. The major failure mechanisms was classified into the fiber matrix debonding, the fiber pull-out, the delamination and the matrix deformation.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.121-128
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• 2019

Supercapacitors are attracting much attention in sensor, military and space applications due to their excellent thermal stability and non-explosion. The ionic liquid is more thermally stable than other electrolytes and can be used as a high temperature electrolyte, but it is not easy to realize a high temperature energy device because the separator shrinks at high temperature. Here, we report a study on electrochemical supercapacitors using a composite electrolyte film that does not require a separator. The composite electrolyte is composed of thermoplastic polyurethane, ionic liquid and fumed silica nanoparticles, and it acts as a separator as well as an electrolyte. The silica nanoparticles at the optimum mass concentration of 4wt% increase the ionic conductivity of the composite electrolyte and shows a low interfacial resistance. The 5 wt% polyurethane in the composite electrolyte exhibits excellent electrochemical properties. At $175^{\circ}C$, the capacitance of the supercapacitor using our free standing composite electrolyte is 220 F/g, which is 25 times higher than that at room temperature. This study has many potential applications in the electrolyte of next generation energy storage devices.