• Journal of Adhesion and Interface
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• v.13 no.2
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• pp.58-63
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• 2012

CFRP chip is the byproduct from carbon fiber reinforced plastic (CFRP) processing. CFRP chip is not simply a waste mainly composed of fine carbon fiber and epoxy resin. CFRP chip keeps matrix to maximize their reinforcing effect. To obtain a uniform length of carbon fiber in CFRP chip, chip was chopped ina mortar. CFRP chip should be purified to get better interface adhesion. Epoxy resin on the carbon fiber was removed by $H_2O_2$ surface etching treatment. Optimal dispersion and fabrication conditions of CFRP chip embedded in phenolic resin were determined by thermal stability for fire retardant applications. CFRP chip-phenolic composite exhibits better mechanical and thermal properties than neat phenolic resin. Surface condition of CFRP chip-phenolic composite was evaluated by static contact angle measurement. Contact angle of CFRP chip-phenolic composite was greater than neat phenolic due to heterogeneous condition of fine carbon fibers. From the evaluation for fire retardant (ASTM D635-06) test, thermal stability of CFRP chip-phenolic composite was found to be improved with higher concentration of CFRP chip.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.918-924
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• 1998

This study has been carried out to investigate the effect of reaction milling time on the synthesis of Ti- TiC p powder synthesised from the elemental titanium and activated carbon by reaction milling(RM), and the effect of vacu­u urn hot pressing temperature and TiC volume fraction on microstructural and mechanical properties of Ti- TiC com­p posite $\infty$ns이idated by vacuum hot pressing(VHP).T The elemental powders of titanium and activated carbon can be converted into Ti- TiC composite powders by reac­t tion milling for about 300hours, and were the average grain size of the as- milled powders has been measured to be a about $5\mu\textrm{m}$. The relative density of Ti- TiC VHPed above $1000^{\circ}C$ during Ihr is about 98% and the mechanical properties o of In- situ Ti- TiC composites are improved by TiC particle dispersed uniformly on titanium matrix. In order to investi­g gate thermal stability of Ti- TiC composite, after annealing at $600^{\circ}C$ for 80hrs micro- Vickers hardness have been per­f formed, and the values have been shown little changed as compared with those before annealing. The compact has b been tested on high temperature compressive test at $700^{\circ}C$ and has showed a high temperature compressive strength of 330MPa in a Ti- 20vol% TiC.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.6
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• pp.342-347
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• 2016

We investigated the effect of $Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3$ (BNKT) modification on the ferroelectric and electric-field-induced strain (EFIS) properties of lead-free $0.97Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3-0.03LaFeO_3$ (BNKTLF) ceramics as a function of BNKT content (x= 0, 0.1, 0.2, 0.3, 0.5, and 1). BNKT-modified BNKTLF powders were synthesized using a conventional solid-state reaction method. As the BNKT content x increased from 0 to 1 the normalized electric-field-induced strain ($S_{max}/E_{max}$) was observed to increase at relatively low fields, i.e., below the poling field. Moreover, BNKTLF-30BNKT showed about 460 pm/V as low as at 3 kV/mm, which is a considerably high value among the lead-free systems reported so far. Consequently, it was confirmed that ceramic-ceramic composite, a mixture of an ergodic relaxor matrix and embedded ferroelectric seeds, is a salient way to make lead-free piezoelectrics practical with enhanced EFIS at low field as well as less hysterical.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.121-127
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• 2013

With the continuing demand for lightweight bicycles, carbon fiber composite materials have been widely used in manufacturing bicycle frames and components. Unlike general isotropic materials, the structural characteristics of composite materials are strongly influenced by the staking directions and sequences of composite laminates. Thus, to verify the design process of bicycles manufactured using composites, structural analysis is considered essential. In this study, a carbon-fiber-reinforced plastic (CFRP) bicycle frame was designed and its structural behavior was investigated using finite element analysis (FEA). By measuring the failure indices of the fiber and matrix under various stacking sequences and loading conditions, the effect of the stacking condition of composite laminates on the strength of the bicycle structure was examined. In addition, the structural safety of the bicycle frame can be enhanced by reinforcing weak regions prone to failure using additional composite laminates.

• 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.

• Journal of the Korea Convergence Society
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• v.13 no.4
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• pp.331-337
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• 2022

Manufactured thermoplastic composite materials to replace the metal materials used as battery housing materials for electric vehicles with lightweight materials. As the matrix material, nylon 6 which is a polymer material was used. Boron Nitrate(BN), which has high thermal conductivity, was used to provide heat dissipation performance. The heat dissipation characteristics of the thermally conductive polymer composite material according to the BN content and particle size were analyzed. The thermal conductivity value increased as the filler content increased, and composite materials particle size of 60 to 70㎛ and BN content of 50%, the thermal conductivity was 1.4 W/mK. The larger the particle size, the wider the inter-particle interface contact surface, which means that a thermal path was formed. wider the interfacial contact surface between the particles, and the thermal path was formed. A battery housing was manufactured using the manufactured thermally conductive polymer composite material, and the temperature change during charging and discharging of the cell was observed, and the possibility as a substitute material for the battery housing was confirmed.

• Membrane Journal
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• v.32 no.6
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• pp.442-455
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• 2022

High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) has been studied as an alternative to low-temperature PEMFC due to its fast activation of electrodes and high resistance to electrode poisoning by carbon monoxide. It is highly required to develop stable PEMs operating at high temperatures even doped by ion-conducting materials for the development of high-performance and durable HT-PEMFC systems. A number of studies have been conducted to develop polybenzimidazole (PBI)-based PEMs for applications in HT-PEMFC due to their high interaction with doped ion-conducting materials and outstanding thermomechanical stability under high-temperature operation. This review focused on the development of PBI-based PEMs showing high performance and durability. Firstly, the characteristic behavior of PBI-based PEMs doped with various ion-conducting materials including phosphoric acid was systematically investigated. And then, a comparison of the physicochemical properties of the PEMs according to the different membrane manufacturing processes was conducted. Secondly, the incorporation of porous polytetrafluoroethylene substrate and/or inorganic composites to PBI matrix to improve the membrane performances was studied. Finally, the construction of cross-linked structures into PBI-based PEM systems by polymer blending method was introduced to improve the PEM properties.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4A
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• pp.353-359
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• 2010

Cementitious matrix based composites are vulnerable to the drying shrinkage crack during the curing process. In this study, the drying shrinkage induced fracture behavior of the fiber reinforced concrete is simulated and the effects of the fiber reinforcement conditions on the fracture characteristics are analysed. The numerical model is composed of conduit elements and rigid-body-spring elements on the identical irregular lattice topology, where the drying shrinkage is presented by the coupling of nonmechanical-mechanical behaviors handled by those respective element types. Semi-discrete fiber elements are applied within the rigid-body-spring network to model the fiber reinforcement. The shrinkage parameters are calibrated through the KS F 2424 free drying shrinkage test simulation and comparison of the time-shrinkage strain curves. Next, the KS F 2595 restrained drying shrinkage test is simulated for various fiber volume fractions and the numerical model is verified by comparison of the crack initiating time with the previous experimental results. In addition, the drying shrinkage cracking phenomenon is analysed with change in the length and the surface shape of the fibers, the measurement of the maximum crack width in the numerical experiment indicates the judgement of the crack controlling effect.

• Composites Research
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• v.36 no.5
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• pp.303-309
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• 2023

In this paper, a Progressive Damage and Failure Analysis (PDFA) modeling method was developed using ABAQUS/EXPLICIT to predict in-plane damage and delamination for Open-Hole Compression (OHC) testing. The proposed PDFA model was constructed based on Hashin criteria and cohesive behavior. The strength and stiffness of OHC specimens with three types of stacking sequences [(45/-45/0₂)₃]_s , [(45/0/-45/90)₃]_s and [45/-45/0/45/-45/90/(45/-45)₂]_s were compared to comprehensively evaluate the validity of the Finite Element(FE) model of PDFA. The strength and stiffness of the OHC specimens were predicted relatively well, with less than a percentage error 10.0 %. For the numerical simulation case for each layup, the damage initiation/evolution of OHC specimens were evaluated for delamination and tension/compression matrix damage before and after failure.

• Journal of Sensor Science and Technology
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• v.33 no.1
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• pp.34-39
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• 2024

Energy harvesting technology that converts the wasted energy resources into electrical energy is emerging as a semipermanent power source for self-powered electronics and wireless low-power sensor systems. Among the various energy conversion techniques, flexible piezoelectric energy harvesters (f-PEHs), using materials with piezoelectric effects, have attracted significant interest because they can harvest a small mechanical energy into electrical signals without constraints of time and space in various environments. In this study, we used a flexible piezoelectric composite film fabricated by dispersing BaHf_xTi_(1-x)O₃ (x = 0, 0.01, 0.05, 0.1) piezoelectric powders inside a polymeric matrix to facilitate f-PEHs. The fabricated f-PEH with optimal Hf contents (x = 0.05) generated a maximum output voltage of 0.95 V and current signal of 130 nA with stable electrical/mechanical disabilities under periodically bending deformations. In addition, we demonstrated a cantilever-type f-PEH and investigated its potential as a sensor by characterizing the output performance under mechanical vibrations at various frequencies. This study provides the breakthrough for realizing self-powered energy harvesting and sensing systems by adopting the lead-free piezoelectric composites under vibrational environments.