• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1169-1175
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• 1994

Five Al2O3/SiC/metal composites with four different particle sizes of green SiC abrasive grains are grown by the directed oxidation of an commercially available Al-alloy. Oxidation was conducted in air at 100$0^{\circ}C$, 96 hours long. Slip casted SiC-fillers were placed on the alloy or SiC powder deposited up to the required layer thickness. Their microstructures are described and measurements of density, elastic constants, frexural strength, fracture toughness and work of fracture are reported. The results are compared with those of commercial dense sintered Al2O3. The properties of produced materials have a strong relationship to not only the properties of Al2O3, SiC, Al and Si but also to the phase share and phase distribution. The composite materials are dense (0.5% porosity), tough (KIC = 3.4~6.4 MPa{{{{ SQRT { m} }}), strong ({{{{ sigma }}B = 170~345 MPa) and reasonably shrinkage free producible. The reinforcements is attained mainly through the plastic deformation of ductile metal phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.425-431
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• 2005

The efficiency of complex slurry preparation route for developing the high performance SiC matrix of $RS-SiC_{f}/SiC$ composites has been investigated. The green bodies for RS-SiC materials prior to the infiltration of molten silicon were prepared with various C/SiC complex slurries, which associated with both the sizes of starting SiC particles and the blending conditions of starting SiC and C particles. The characterization of Rs-SiC materials was examined by means of SEM, EDS and three point bending test. Based on the mechanical property-microstructure correlation, the process optimization is also discussed. The flexural strength of Rs-SiC materials greatly depended on the content of residual Si. The decrease of starting SiC particle size in the C/SiC complex slurry was effective for improving the flexural strength of RS-SiC materials.

• Advanced Composite Materials
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• v.18 no.2
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• pp.167-185
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• 2009

Environmental problems caused by extensive use of polymeric materials arise mainly due to lack of landfill space and depletion of finite natural resources of fossil raw materials like petroleum or natural gas. The substitution of synthetic petroleum-based resins with natural biodegradable resins appears to be one appropriate measure to remedy the above-mentioned situation. This study presents the development of a composite that uses environmentally degradable starch-based resin as matrix and natural mineral basalt fibres as reinforcement, and investigates the fibre's and the composite's mechanical properties. The tensile strength of single basalt fibres was verified by means of single fibre tensile tests and statistically investigated by means of a Weibull analysis. Prepreg sheets were manufactured by means of a modified doctor blade system and hot power press. The sheets were used to manufacture specimens with fibre volume contents ranging from 33% to 61%. Specimens were tested for tensile strength, flexural strength and interlaminar shear strength. Composites manufactured during this study exhibited tensile and flexural strength of up to 517 MPa and 157 MPa, respectively.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.250-257
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• 2000

The feasibility of synthesizing SiC-AlN solid solution by field-activated combustion synthesis was demonstrated. At lower fields of 8-16.5V/cm, composites of AlN-rich and SiC-rich phases were synthesized, but at fields of 25-30 V/cm, the product was a 2H structure solid solution. Combustion synthesis of the solid solution by nitridation of aluminum with silicon carbide under a nitrogen gas pressure of 4-8 MPa was also investigated. The maximum combustion temperature and wave propagation velocity were found to be influenced by the electric field in the field-activated combustion synthesis, and by the green density and nitrogen pressure in the combustion nitridation. In both cases the formation of solid solutions is complete within seconds, considerably faster than in conventional methods which require hours.

• International Journal of Safety
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• v.10 no.1
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• pp.1-4
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• 2011

The fuel cell is one of the green energy receiving a lot of attention. Among the fuel cells, it is generally referred to SOFC(solid oxide fuel cell) which is made up composites of a solid. SOFC has excellent merits in the side of environment and energy. However because of the high operating temperature, it has economic loss by the using of expensive materials and problems of structural instability by thermal stresses. Therefore, this study aims to the effect of analysis by the FEMLAB. The results have deformations and the maximum stresses from the variation of the thickness of vulnerability spots. The deformation shows expansion as 0.82% and the stress ${\sigma}_{xx}$ is 392MPa in electrolyte and -56.31MPa in anode. When increasing or decreasing the thickness to 50% of the reference thickness about the electrolyte which is vulnerable spots.

• Polymer(Korea)
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• v.24 no.1
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• pp.97-104
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• 2000

PAN-based activated carbon fibers/phenolic resin matrix composites (ACFCs) were manufactured via molding process with oxidized carbon fabrics (plain-type) and phenolic resin (resole-type) compounded by 70 : 30 wt%. The green body (as molded) was submitted to carbonization (at 100$0^{\circ}C$) in an inert environment and activation (at 700, 800, 900 and 100$0^{\circ}C$) in a $CO_2$ environment. In this work, the influence of activation temperatures was investigated in surface properties, such as pH, acid- and base-values by titration method, and in adsorption properties, i.e., specific surface area and pore structures by BET-method of the composites. Also, the pressure drops of the specimens were calibrated by ASTM. As a result, the activation temperature influenced the surface property of ACFCs. When the activation temperature was higher than 90$0^{\circ}C$, the surface was gradually developed in basic nature. And, the evolutions of specific surface area, total pore volume and pore size distribution of ACFCs could be easily confirmed the dependence on the activation temperature. Among them, well-developed pore structure from adsorption characteristics was changed of the ACFCs activated at 90$0^{\circ}C$. Also, the pressure drop was slightly decreased with increasing the temperature due to increasing the burn-off with heat treatment temperature of ACFCs.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.43-49
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• 1999

Gas pressure sintered silicon nitride based composites with 0~5wt% $\beta$-Si3N4 whiskers were prepared. The whiskers were unidirectionally oriented by a modified tape casting technqiue and green bodies with various microstructure were formed by changing stacking sequences of sheets cut from the tape. Orientations of the large elongated grains of the sample after gas pressure sintering were the same as the those of the whiskers of green body, and the sintering shrinkage and mechanical properties of sintered sample were consistent with the microstructural characteristics. In case of unidirectional samples, the sintering shrinkage normal to whisker alignment direction was larger than that parallel to the direction. The shrinkage difference inceaed as the whiskercontent increaed. As whisker content increaed, the crack length normal to and parallel to tape casting direction became shorter and larger, respectively. Although the grain size increased by th whisker addition, the flexural strength of unidirectional samples was not lower than that of smaple without the whisker. In case of crossplied and 45$^{\circ}$rotated samples, the anisotropy of mechanical preoperties disappeared.

• Journal of Adhesion and Interface
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• v.23 no.3
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• pp.87-93
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• 2022

To analyze the interfacial property between the fiber and the matrix, work of adhesion was used generally that was calculated by surface energies. In this paper, it was determined what types of contact angle measurement methods were more accurate between static and dynamic contact angle measurements. 4 types of glass fiber and epoxy resin were used each other to measure the contact angle. The contact angle was measured using two types, static and dynamic contact angle methods, and work of adhesion, W_a was calculated to compare interfacial properties. The interfacial property was evaluated using microdroplet pull-out test. Generally, the interfacial property was proportional to work of adhesion. In the case of static contact angle, however, work of adhesion was not consistent with interfacial property. It is because that dynamic contact angle measurement comparing to static contact angle could delete the error due to microdroplet size to minimize the surface area as well as the meniscus measuring error.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 2000.06a
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• pp.195-214
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• 2000

The high-speed steel (shorten as HSS) consists of Fe and several kinds of transition metal carbides. The cutting tools or wear-resistant materials made from HSS experience relatively high thermal shock because a coolant such as water or oil is flowed over the surface of heated HSS. The purpose of this research is to increase the hardness, strength, fracture toughness and thermal shock resistance of HSS. A possible strategy is to incorporate a hard ceramic material with high strength in HSS matrix. This paper describes the processing, microstructure and mechanical properties of the oriented unidirectional mullite fiber/HSS composite. The unidirectional mullite fibers of 10${\mu}{\textrm}{m}$ diameter were dispersed by the ultrasonic irradiation of 38 kHz in an ethylenglycol suspension containing HSS powder of 11${\mu}{\textrm}{m}$ median size. The dried green composites with 4-68 vol% fibers were hot-pressed for 2h at 100$0^{\circ}C$ in Ar atmosphere under a pressure of 39 MPa. The higher density was achieved in the composite with a lower content of fibers. The oriented unidirectional fibers were well dispersed in the HSS matrix. The average distance between the center of fibers in the cross section was close to the value calculated from the fiber fraction. No reaction occurred at the interfaces between HSS and mullite fibers in the composites. The composite with 13.6 vol% fibers showed 100 MPa of four point flexural strength at room temperature. The thermal expansion of composite with heating was influenced by the orientation of mullite fibers.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.148-156
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• 2007

The fiber dispersion in fiber-reinferced cementitious composites is a crucial factor with respect to achieving desired mechanical performance. However, evaluation of the fiber dispersion in the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) is extremely challenging because of the low contrast of PVA fibers with the cement-based matrix. In the present work, a new evaluation method is developed and demonstrated. Using a fluorescence technique on the PVA-ECC, PVA fibers are observed as green dots in the cross-section of the composite. After capturing the fluorescence image with a charged couple device (CCD) camera through a microscope, the fiber dispersion is evaluated using an image processing technique and statistical tools. In this image processing technique, the fibers are more accurately detected by employing an enhanced algorithm developed based on a discriminant method and watershed segmentation. The influence of fiber orientation on the fiber dispersion evaluation was also investigated via shape analyses of fiber images.