• 연구논문집
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• s.23
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• pp.165-171
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• 1993

$Si_3N_4/Sic$. nano-composites were fabricated by hot-pressing, gas pressure sintering. The composites contained up to 50 wt. % of SiC. The mechanical properties such as strength, toughness, and hardness of the composite are compared each other. The flexural strength of the composites was improved significantly by introducing fine SiC particles into $Si_3N_4$ matrix, while the fracture toughness was not improved. The increase in flexural strength is attributed to the formation of uniformly elongated $\beta -Si_3N_4$ grains as well as the reduction of grain size.

• Journal of Technologic Dentistry
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• v.37 no.3
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• pp.107-113
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• 2015

Purpose: This study provided the basic data for selecting the zirconia blocks by comparing the mechanical properties of the all ceramic crown between the domestic, import, translucent and shade blocks that were used in clinically. Methods: Currently, the most commercial block of five types(one import and two domestic block which is the translucent and shade) were used. It were elucidated by means of three point bending test, hardness test, FE-SEM observations and EDX analysis. The results were analyzed using a one-way ANOVA and Scheffe post hoc test for significant findings. Results: For flexural strength, LT specimen was the highest as 733.1 MPa, followed by JT specimen(712.0 MPa), ZT specimen(646.0 MPa), LS specimen(553.1 MPa), JS specimen(429.0 MPa). One-way ANOVA showed statistically significant difference between groups for flexural strength(p<0.05). For hardness, ZT specimen was the highest as 1556.5 Hv, followed by JT specimen(1540.3 Hv), LT specimen(1512.3 Hv), JS specimen(1472.0 Hv), LS specimen(1353.3 Hv). One-way ANOVA showed statistically significant difference between groups for hardness(p<0.05). Conclusion: Domestic block was higher than import block for flexural strength, and translucent block was higher than shade block for flexural strength. However, all blocks showed clinically acceptable range. There was no significant difference in hardness between domestic and import blocks. And significant difference was observed in translucent and shade blocks.

• Restorative Dentistry and Endodontics
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• v.43 no.2
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• pp.26.1-26.12
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• 2018

Objective: The purpose of this study was to investigate the degree of conversion (DC) and mechanical properties of a microhybrid Filtek Z250 (3M ESPE) resin composite after aging. Method: The specimens were fabricated using circular molds to investigate Vickers microhardness (Vickers hardness number [VHN]) and DC, and were prepared according to ISO 4049 for flexural strength testing. The initial DC (%) of discs was recorded using attenuated total reflectance-Fourier transforming infrared spectroscopy. The initial VHN of the specimens was measured using a microhardness tester under a load of 300 g for 15 seconds and the flexural strength test was carried out with a universal testing machine (crosshead speed, 0.5 mm/min). The specimens were then subjected to thermocycling in $5^{\circ}C$ and $55^{\circ}C$ water baths. Properties were assessed after 1,000-10,000 cycles of thermocycling. The surfaces were evaluated using scanning electron microscopy (SEM). Data were analyzed using 1-way analysis of variance followed by the Tukey honest significant difference post hoc test. Results: Statistical analysis showed that DC tended to increase up to 4,000 cycles, with no significant changes. VHN and flexural strength values significantly decreased upon thermal cycling when compared to baseline (p < 0.05). However, there was no significant difference between initial and post-thermocycling VHN results at 1,000 cycles. SEM images after aging showed deteriorative changes in the resin composite surfaces. Conclusions: The Z250 microhybrid resin composite showed reduced surface microhardness and flexural strength and increased DC after thermocycling.

• Journal of the Korean Ceramic Society
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• v.30 no.7
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• pp.549-556
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• 1993

Interfacial shear strength plays an important role in determining the mechanical properties of a fiber-reinforced ceramic composites. In this study, the effect ofinterlayer thickness on mechanical properties of Nicalon-fiber-reinforced SiC composites fabricated via polymer solution infiltration/chemical vapor infiltration (PSI/CVI) was studied. It was found that the flexural strength and fracture toughness of the composites were increased with the interlayer thickness and showed maximum value at the interlayer thickness of 0.66${\mu}{\textrm}{m}$. Typical flexural strength and fracture toughness of Nicalon-fiber-reinforced SiC composites with interlayer thickness of 0.66${\mu}{\textrm}{m}$ were 391.7$\pm$34.6MPa and 15.1$\pm$1.8MPa.m1/2, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.31-31
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• 2010

Nano particles (10nm $SiO_2$) were silane-treated in order to modify the surface characteristics in a epoxy nanocomposite. Then, micro particles ($3{\mu}m$ SiO2) were poured into the epoxy nanocomposite using various mixing process and epoxy/micro-and-nanomixed composites (EMNC) were prepared. The thermal (Tg) and mechanical (tensile and flexural strength) properties were measured by DSC, DMA and UTM and the data was estimated by Weibull plot.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.127-132
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• 2012

In this study, ambient temperature curing artificial aggregate were developed by using crushed-stone sludge. In order to evaluate the mechanical properties, the artificial aggregate was tested on 7 items. Test results showed that the artificial aggregate mostly satisfied the basic requirements of normal aggregate. The concrete with the artificial aggregate made by weathered rock and granite sludge was tested on the compressive test and flexural test. From the test results, It is confirmed that the concrete with the granite artificial aggregate develope the higher compressive strength than the crushed rock aggregate and the concrete with artificial aggregate concrete have the lower elastic modulus and flexural strength than the concrete with crushed rock aggregate.

• Composites Research
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• v.28 no.3
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• pp.136-141
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• 2015

The stitching process has been widely utilized for the improvement of through-thickness property of the conventional laminated composites. This paper reports the effects of stitching on the flexural and interlaminar shear properties of multi-axial warp knitted (MWK) composites in order to identify the mechanical property improvements. In order to minimize the geometric uncertainties associated with the stacking pattern of fabrics, the regular lay-up was considered in the examination of the stitching effect. The key parameters are as follows: the stitch spacings, the stitching types, the stitching location, and the location of compression fixture nose. These parameters have little effect on the flexural and interlaminar shear properties, except for the case of stitching location. However, the geometry variations caused by the stitching resulted in minor changes to the mechanical properties consistently. Stitching on the $0^{\circ}$ fibers showed the lowest flexural strength and modulus (12% reduction for both properties). The stitch spacing of 5 mm resulted in 8% reduction for the case of interlaminar strength compared with that of 10 mm spacing.

• Computers and Concrete
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• v.18 no.2
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• pp.279-295
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• 2016

A new innovative composite material is textile reinforced cementitious composite (TRCC). To achieve high flexural performance researchers suggest polymer modification of TRCC matrices. In this study, nine ready mix repair mortars commonly used in construction industry and the production of TRCC elements were examined. Mechanical properties such as compressive and flexural strength, drying shrinkage were studied. Being a significant durability concern, alkali silica reaction tests were performed according to related standards. Results showed that, some ready repair mortar mixes are potentially reactive due to the alkali silica reaction. Two of the ready mortar mixes labelled as non-shrinkage in their technical data sheets showed the highest shrinkage. In this experiment, researchers designed new matrices. These matrices were fine grained concretes modified with polymer additives; latexes and redispersible powders. Two latexes and six redispersible powder polymers were used in the study. Mechanical properties of fine grained concretes such as compressive and flexural strengths were determined. Results showed that some of the fine grained concretes cast with redispersible powders had higher flexural strength than ready mix repair mortars at 28 days. Matrix composition has to be designed for a suitable consistency for planned production processes of TRCC and mechanical properties for load-carrying capacity.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.269-272
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• 2002

UV curing technology becomes important in various sectors of applications due to the high efficiency, environmental protection, and saving of energy. The effect of different proportion of vinylester (VE) and unsaturated polyester (UP) for VE/UP blend system was investigated in context of mechanical properties. The compositions of VE/UP blend were varied within 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0 by weight percent. 1 wt% 1-hydroxy-cyclohexyl-phenyl-ketone was used as photoinitiator. The used intensity of UV light was in the range of $40~70 mW/\textrm{cm}^2$. The flexural strength of vinylester was not sensitive to the intensity of UV light. But the unsaturated polyester was very sensitive to the intensity of UV light. The flexural strength of vinylester was always superior to that of unsaturated polyester. The addition of the vinylester increased the flexural strength of blend system.

• Advances in concrete construction
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• v.6 no.6
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• pp.631-643
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• 2018

The focus of this paper is given to the investigation of mechanical properties of steel fibre reinforced self-compacting concrete after being exposed to fire. The research programme covered tests of two sets of beams: specimens subjected to fire and specimens not subjected to fire. The fire test was conducted in an environment mirroring one of possible real fire situations where concrete surface for an extended period of time is directly exposed to flames. Micro-cracking of concrete surface after tests was digitally catalogued. Compressive strength was tested on cube specimens. Flexural strength and equivalent flexural strength were tested according to RILEM specifications. Damages of specimens caused by spalling were assessed on a volumetric basis. A comparison of results of both sets of specimens was performed. Significant differences of all tested properties between two sets of specimens were noted and analysed. It was proved that the limit of proportionality method should not be used for testing fire damaged beams. Flexural characteristics of steel fibre reinforced self-compacting concrete were significantly influenced by fire. The influence of fire on properties of steel fibre reinforced self-compacting concrete was discussed.