• Korean Journal of Materials Research
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• v.13 no.4
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• pp.213-218
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• 2003

Fibrous monolithic control of$ Al_2$$O_3$ -$ZrO_2$composite was investigated by multi-pass extrusion process. To obtain sound $Al_2$$O_3$-X $O_2$sintered bodies, burning out and sintering process were carefully carried out. The sintered bodies showed continuous, fibrous monolithic microstructure without any swelling. Many microcracks were observed at the $Al_2$$O_3$-$ZrO_2$interfaces due to the mismatching of thermal expansion coefficient between $Al_2$$O_3$ and $ZrO_2$phase. Most of m- $ZrO_2$grains included twin defects such as (001), (010) and (011) type to accommodate the phase transformation induced stress.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1435-1450
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• 2004

The investigation, which includes the material homogenization and the calculation of local stress concentration of long-fibrous composites in a microscopic level, has been performed to analyze the behavior of fiber-reinforced composites by using finite element method. In order to carry out this study, the finite element models of composites have been generated by the idealized arrays as square and hexagonal-packed type. In the FE analysis, the boundary conditions of micromechanical finite element method(MFEM) have been defined and verified by comparing with the results from multi-cells, and the effective material properties of composites composed of graphite/epoxy have been also evaluated by rules of mixture. For acquiring the relation between the global and local behaviors of composites, the magnifications of strain, stress, and interfacial stress of composites subjected to a longitudinal and transverse loading respectively have been calculated. And the magnifications have been proposed as the stress concentration in the microscopic level at composite material.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.60.2-60
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• 2003

• Proceedings of the Materials Research Society of Korea Conference
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• 2004.05a
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• pp.47-47
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• 2004

• Journal of Periodontal and Implant Science
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• v.26 no.1
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• pp.68-79
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• 1996

To investigate the efficiency of a fibrous collagen membrane(FCM) composed of bovine skin type I atelocollagen as a carrier for BMP, partially purified bovine BMP/FCM($0.3mg/10{\times}5{\times}1mm$) composites were implanted into the dorsal subcutaneous tissue of rats. FCM alone was also implanted as a control. The implants were harvested at 1, 2, 3, and 10 weeks after implantation, then prepared for routine light microscopic observation. The FCM alone did not induce osteogenesis and revealed no specific foreign body reaction nor was there any definite resorptive evidence for 10 weeks after implantation, while the BMP/FCM composites induced favorable bone formation in a process that resembled an endochondral and direct ossification mode. At 10 weeks, the well formed bone confined to embedded collagen fibers revealed hematopoietic marrow between bony trabeculae without evidence of resorptive or degenerative changes . These findings support the suggestion that BMP may induce undifferentiated mesenchymal cells into either chondroblasts or osteoblasts or both independantly according to the chemico- physical characteristics of the carrier, which develops the endochondral and/or direct bone formation process, and suggest that the FCM may be a favorable carrier for BMP.

• Composites Research
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• v.32 no.6
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• pp.368-374
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• 2019

Basalt fiber reinforced epoxy composites with inorganic filler (BFRP-F) such as Mg(OH)₂ (magnesium hydroxide), Al(OH)₃ (aluminum hydroxide), Al₂O₃ (aluminum oxide) and AlOOH (boehmite) were prepared by hand lay-up and hot pressing. The combustive properties of BFRP-F were improved comparing with basalt fiber reinforced epoxy composite (BFRP) without inorganic filler. At a 30 wt% resin content, the limited oxygen index (LOI) of BFRP is 28.9, which is higher than that of epoxy (21.4), and the LOI of BFRP-F is higher than that of BFRP. The BFRP-F showed the lower peak heat release rate (PHRR), total heat release (THR) and total smoke release rate (TSR) than those of BFRP. We confirmed that the flame retardant properties of the composite were improved by the addition of inorganic filler through the dehydration reaction and oxide film formation.

• Korean Journal of Materials Research
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• v.23 no.9
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• pp.531-536
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• 2013

This paper investigates the effect of prolonged high temperature exposure on concentric laminated $Al_2O_3-ZrO_2$ composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was $2-3{\mu}m$ thick. An alternate lamina was composed of 75%$Al_2O_3$-(25%m-$ZrO_2$) and t-$ZrO_2$ ceramics. The composite was sintered at $1500^{\circ}C$ and subjected to $1450^{\circ}C$ temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-$ZrO_2$ layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.

• Korean Journal of Materials Research
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• v.15 no.12
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• pp.751-755
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• 2005

Fibrous $Al_2O_3-(m-ZrO_2)/t-ZrO_2$ composites having core/shell structure were fabricated by multi-extrusion process. The effect o volume fraction between core ($Al_2O_3-(m-ZrO_2)$) and shell ($t-ZrO_2$ was investigated to understand the relationship between microstructure and material properites, in which the volume fractions of core and shell were varied as 40:60, 50:50 and 60:40. The material properties o hardness and bending strength were increased as the volume fraction of core was increased, and their maximum values were about 1320 Hv and 750MPa, respectively. However, as the volume fraction of core increased, the values of relative density and fracture toughness were decreased from 97.1 to $96.5\%$ and from $6.5MPa{\cdot}m^{1/2}$ to $5.7MPa{\cdot}m^{1/2}$, respectively.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.215-222
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• 1995

Anisotropic pitch-based C-type and hollow carbon fibers can obtain wider shear stresses during the spinning and induce higher molecular orientation than that of round along the fiber axis. These fibers reinforced unidirectional epoxy composites were prepared by hot-press moulding method and perpendicular and parallel thermal conductivities of the composites were measured by a steady-state meth od. In the case of round carbon fibers reinforced epoxy composites(H-CF/EP), thermal anisotropic factor showed nearly 50, while those of H-CF/EP and C-CF/EP showed about 130 and 118, respectively. As a result, both H-CF/EP and C-CF/EP had an excellent directional thermal conductivity to distribute heat, above 200 %.

• 연구논문집
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• s.29
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• pp.151-162
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• 1999

In general, manufacturing processes of thermosetting composites consist of mold filling and resin cure. The important parameters used in modeling and designing mold filling are the permeability of the fibrous preform and the viscosity of the resin. To consolidate a composite, resin cure or chemical reaction plays an essential role. Cure kinetics. Therefore, is necessary to quantify the extent of chemical reaction or degree of cure. It is also important to predict resin viscosity which can change due to chemical reaction during mold filling. There exists a heat transfer between the mold and the composite during mold filling and resin cure. Cure kinetics is also used to predict a temperature profile inside composite. In this study, a new scheme which can determine cure kinetics from dynamic temperature scaning was proposed. The method was applied to epoxy resin system and was verified by comparing measurements and predictions.