• Composites Research
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• v.35 no.1
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• pp.23-30
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• 2022

Polycarbosilane(PCS) is an important precursor for melt-spinning the silicon carbide(SiC) fibers and manufacturing ceramics. The PCS is a metal-organic polymer precursor capable of producing continuous SiC fibers having excellent performance such as high-temperature resistance and oxidation resistance. The SiC fibers are manufactured through melt-spinning, stabilization, and heat treatment processes using the PCS manufactured by synthesis, purification, and control of the molecular structure. In this paper, we analyzed the effect of purification of unreacted substances and low molecular weight through solvent treatment of PCS and the effect of heat treatment at various temperatures change the polymerization and network rearrangement of PCS. Especially, we investigated the complex viscosity and structural arrangement of PCS precursors according to solvent treatment and heat treatment through the rheological properties.

• Polymer(Korea)
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• v.31 no.2
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• pp.160-167
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• 2007

This paper proposes a model for the solutions predicting the coefficient of thermal expansion of composites including fiber-like shaped$(a_1>a_2=a_3)$ and disk-like shaped$(a_1=a_2>a_3)$ inclusions like two dimensional geometries, which was analyzed by one axis and a single aspect ratio, $(\rho_\alpha=a_1/a_3)$. The analysis follows the procedure developed for elastic moduli by using the Lee and Paul's approach. The effects of the aspect ratio on the coefficient of thermal expansion of composites containing aligned isotropic inclusions are examined. This model should be limited to analyze the composites with unidirectionally aligned inclusions and with complete binding to each other of both matrix and inclusions having homogeneous properties. The longitudinal coefficients of thermal expansion $\alpha_{11}$ decrease and approach the coefficient of thermal expansion of filler, as the aspect ratios increase. However, the transverse coefficients of thermal expansion $\alpha_{33}$ increase or decrease with the aspect ratios.

• Journal of Conservation Science
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• v.34 no.6
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• pp.517-524
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• 2018

This study using a method different from those employed previously, the anatomical characteristics of paper-mulberry wood were confirmed by observing three different sections. In addition, the factors affecting the pulp and papermaking processes were analyzed in terms of morphological properties such as the fiber length and width, lumen width, and chemical composition of the paper-mulberry bast fiber. The anatomical characteristics of the paper-mulberry wood were a ring porous or semi-ring porous structure with the vessels showing solitary pore and radial array. The medullary ray of the tangential section showed 1-3 rows and common helical thickening. Consequently, the paper-mulberry wood has the same anatomical characteristics throughout. The morphological characteristics of the paper-mulberry bast fiber are a fiber length of 6.58 to 9.01 mm, fiber width of 15.85 to $27.80{\mu}m$, lumen width of 4.50 to $12.54{\mu}m$. The D sample of Gangwon was the most suitable for the pulp and papermaking processes, in terms of its derived morphological ratios. Comparing the chemical compositions, the C sample of Gyeongsang had a high holocellulose content (90%). Thus, the findings herein will aid in determining the quality of Korean paper post production.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.4
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• pp.159-165
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• 2021

The fiber composites have been investigated as lightweight structure material platforms for aerospace applications because their strength can be enhanced by adding reinforcement without a significant increase in weight. In this study, the fabrication and characterization of carbon nanotube (CNT) reinforced glass fiber composites are demonstrated to enhance the tensile strength of longitudinal direction along the glass fibers. Due to the reinforcement of CNT in epoxy layers, the yield strength of fiber/epoxy composites is enhanced by about 10 %. Furthermore, using scanning electron microscopy, analysis of fracture surfaces shows that mixed CNT in epoxy layers acts as necking agents between fractured surfaces of fiber/epoxy; thereby, initiation and evolution of crack across fiber composite can be suppressed by CNT necking between fractured surfaces.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.1
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• pp.73-87
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• 1996

The mechanical properties of 2D ceramic composites fabricated bythe newly developed powder infiltration and subsequent multiple impregnation process were characterised by both 3-point flexure and tensile tests. These tests were performed with strain gauge and acoustic emission instrument. The woven fabric composites used for the test have the basic combinations of $Al_{2}$$O_{3}$ fabric/$Al_{2}$$O_{3}$ and SiC fabric (Tyranno)/SiC. Uniaxially aligned SiC fibre(Textron SCS-6)/SiC composites were also tested for comparison, The ultimate flexural strength and first-matrix cracking stress of SiC fabric/SiC composite with 73% of theoretical density were about 300 MPa and 77 MPa respectively. However, the ultimate tensile strengths of composite were generally one third of flexural strengths, and first-matrix cracking stress in a tension test was also much lower than the value obtained from flexure test. The lower mechanical properties measured by tension test were analysed quantitatively bythe differences in stressed volume using Weibull statistics. This showed that the ultimate strength and the firs-tmatrix cracking stress of woven laminate composites were mainly determined bythe gauge length of fibres and the stressed volume of matrix respectively. Incorporation of SiC whiskers into the matrix increased first-matrix cracking stress by increasing the matrix failure strain of composites.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1238-1245
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• 1988

Friction and wear characteristics of short fiber reinforced and particulate filled composites were investigated experimentally. Two kinds of fiber composites, chopped graphite fiber reinforced PAI(polyamide-imide) and glass fiber reinforced PAI, and a particulate composite, TiO$_{2}$ powder filled PAI, were selected for the friction and wear test since these are important engineering materials based on a new high temperature engineering plastic. All the specimens were cut into proper size for cylinder-on-plate type wear test. Frictional forces were measured by employing a load transducer and wear rates were calculated by measuring weight loss during wear test. The experimental results are reported in this paper and carefully discussed to explain the friction and wear behavior qualitatively. The frictional behavior is interpreted by considering four basic friction components which are believed to the genesis of friction and the wear behavior is explained by applying delamination theory of wear.

• Polymer(Korea)
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• v.32 no.4
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• pp.359-365
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• 2008

We have fabricated a novel thermo-responsive nanofibrous surfaces by grafting PIPAAm by electron beam irradiation onto poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) nanofibrous mats. The electrospun PHBV nanofiber structures revealed randomly aligned fibers with average diameter of 400 nm. Increased atomic percent of nitrogen was observed on the PIPAAm-grafted PHBV mats after electron beam irradiation determined by ESCA. The amounts of PIPAAm-grafted onto PHBV films were $6.49{\mu}g/cm^2$ determined by ATR-FTIR. The PIPAAm-grafted surfaces exhibited decreasing contact angles by lowering the temperature from 37 to $20^{\circ}C$, while ungrafted PHBV surfaces had negligible contact angle change. This result indicates that PIPAAm surfaces, which are hydrophobic at the higher temperature, became markedly more hydrophilic in response to a temperature reduction due to spontaneous hydration of the surface-grafted PIPAAm. Thermo-responsive nanofibers showed good tissue compatibility. Cultured cells were well detached and recovered from the surfaces by changing culture temperature from 37 to $20^{\circ}C$.

• Journal of the Korean Wood Science and Technology
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• v.41 no.1
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• pp.51-57
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• 2013

In order to know the shear performances of a bolted connection in reinforced glulam depending upon the combination of textile glass fiber, a tensile-type shear test was conducted. Textile glass fiber was used as a reinforcement, whose glass fiber arrangement was a plain weaving type or a diagonal cloth type. Reinforced glulam was made up of 5 plies and it was produced by inserting and laminating the plies between laminas depending upon a changed insert position and combination form of textile glass fiber. Tensile-type shear test specimens were a steel plate insert-type and joined at end-distance 7D with bolts whose diameter 12 or 16 mm. In textile glass fiber reinforced glulam, whose volume ratio was 1%, the yield shear strength of a 12 mm bolted connection increased by 10% when a test specimen had reinforced internal layers than when external layers were reinforced. As for textile glass fiber reinforced glulam, whose volume ratio was 2%, the yield shear strength of a 12 mm bolted connection increased significantly by about 22% compared to the bolted connection of non-reinforced glulam, and the yield shear strength of a 16 mm bolted connection was improved by about 20% compared to the bolted connection of non-reinforced glulam.

• Composites Research
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• v.26 no.1
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• pp.14-20
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• 2013

The electrospun PVDF containing CNT was made for fabricating materials of the actuator. The electrochemical and their actuating movement were evaluated for the actuator performance in the electrochemical environment. The actuator (which was fabricated by electrospinning) had some advantages, i.e., good dispersion and flexible properties. In the electrospinning process, the final product would have different forms based on different essential factors. In this work, electrospun nanofibers were aligned by using the drum-type collector, and the morphology was identified via the field emission-scanning electron microscope (FE-SEM). The uniform dispersion of CNT in PVDF nanofiber was observed by electron probe X-ray micro-analysis (EPMA) test. The results of tensile strength and electrical resistivity provided the aligned state. The electrospun CNT/PVDF nanofiber sheet on the aligned direction showed better mechanical and electrical properties than the case of the vertically-aligned direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheets were compared with the cast PVDF sheet for actuator application. Electrospun CNT/PVDF nanofiber sheet exhibited much better the case of actuator performance than cast neat PVDF actuator, due to the excellent electrical connecting areas.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.349-356
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• 2018

In this study, material properties of steel fiber reinforced high strength concrete (FRHSC) with the compressive strength of about 120MPa were modeled. Steel fiber content of 1.0%, 1.5%, and 2.0% was considered as experimental variable. First of all, compressive strength tests were carried out to determine compressive characteristics of concrete, and compressive stress-strain curves were modeled. For conventional concrete with moderate compressive strength, the stress-strain curves are in the form of parabolic curves, but in the case of high strength concrete reinforced with steel fiber, the curves increase linearly in the form of the straight line. In addition, to understand the tensile properties of FRHSC, the crack mouth opening displacement (CMOD) test was performed, and the tensile stress-CMOD curve was calculated through inverse analysis. When the steel fiber content increased from 1.0% to 1.5%, there was a significant difference of tensile strength. However, when the amount of steel fiber was increased from 1.5% to 2.0%, there was no significant difference of tensile strength, which might result from the poor dispersion and arrangement of steel fiber in concrete.