• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.143-153
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• 1988

In order to synthesize the partially stabilized $\alpha$-Sialon, A1N and Y2O3 were added to synthesized $\alpha$-Si3N4. The phase composition, mechanical properties, micro structure, etc, of the synthesized $\alpha$-Sialon were investigated. Partially stabilized $\alpha$-Sialon ceramics could be synthesized from the composition which was a little deviated from x=0.4, x=0.6 composition along the Si3N4.0.1Y2O3:0.9AlN tie line at 1750-180$0^{\circ}C$ for 2 hrs in N2 atmosphere. It is assumed that A1N is more closely related than Y2O3 to the formation of $\alpha$-Sialon, and that A1N is more easily dissolved into $\alpha$-structure than into $\beta$-structure. In Ya2O3-rich phase mechanical properties were observed to be poor because of formation of mellilite, grain growth, and thermal decomposition of $\alpha$-Sialon. The maximum values of M.O.R, KIC and hardness are 723 MPa, 4.5MN/㎥/2 and 19.3 GPa, respectively, and they were observed for the $\alpha$-Sialon ceramics sintered at 178$0^{\circ}C$.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.381-384
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• 2008

This study investigated spalling prevention and fire resistance properties of the high strength concrete using pre-mixed cement containing fiber to prepare the method for the effective throwing of hybrid fiber. For result of a fire test, almost specimens were protected from fire except 15% of W/C. Totally, the pre-mixed cement containing fiber was favorable compared with passive mixing method for the spalling prevention. It is more effective to prevent spalling caused by fine diversion of fiber even in high strength concrete because it contained many corporate materials. Moreover, the temperature history of the side steel bar on the column test with pre-mixed cement containing fiber did not over 538$^{\circ}C$ which is the average for the standard of fire resistance performance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.291-294
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• 1999

The effect of AI$_2$O$_3$+Y$_2$O$_3$additives on fracture toughness of $\beta$-SiC-ZrB$_2$composites by hot-pressed sintering were Investigated. The $\beta$-SiC-ZrB$_2$ ceramic composites were hot-presse sintered and annealed by adding 1, 2, 3wt% AI$_2$O$_3$+Y$_2$O$_3$(6:4wt%) powder as a liquid forming additives at 195$0^{\circ}C$ for 4h. In this microstructures, no reactions were observed between $\beta$-SiC and ZrB$_2$, and the relative density Is over 90.79% of the theoretical density and the porosity decreased with increasing AI$_2$O$_3$+Y$_2$O$_3$ contents. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed the highest of 5.5328MPa . m$^{1}$2/ for composites added with 2wt% AI$_2$O$_3$+Y$_2$O$_3$ additives at room temperature. But the standard deviation of fracture toughness of specimens decreased with increasing AI$_2$O$_3$+Y$_2$O$_3$ contents and showed the highest of 0.8624 for composite tilth 1wt%, AI$_2$O$_3$+Y$_2$O$_3$additives.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1545-1547
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-Sic-$TiB_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_3$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and YAG($Al_{5}Y_{3}O_{12}$). The relative density and the mechanical properties of composites were increased with increasing $Al_{2}O_{3}+Y_{2}O_3$ contents because YAG of reaction between $Al_{2}O_3$ and $Y_{2}O_3$ was increased. The Flexural strength showed the highest value of 432.5MPa for composites added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature. Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism. the fracture toughness showed 7.1MPa${\cdot}m^{1/2}$. For composites added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature The electrical resistivity and the resistance temperature coefficient respectively showed the lowest of 6.0${\sim}10^{-4}{\Omega}{\cdot}$ cm and 3.1${\times}10^{-3}/^{\circ}C$ for composite added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of 25$^{\circ}C$ to 700$^{\circ}C$.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.515-524
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• 2008

The ultimate behavior of high-tension bolted joints with various plate thickness and bolt size is investigated using nonlinear F.E. analysis and experimental study. The relation with sliding load, bolt deformation, and failure modes are presented based on plate thickness and bolt size. Three kinds of the bolt diameter(M20, M22, M24) and five types of the steel plates (l2mm, 16mm, 20mm, 30mm, 40mm) are considered for the ultimate behavior of the bolted joints. The numerical model, constructed by commercial F.E. program, ABAQUS, of ultimate behavior of bolted joints is introduced and verified by experimental results. The force-displacement and force-axial strain relations are measured and compared with the results by 3D finite element analysis.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1-6
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• 2004

In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective distance can be used to evaluate the failure criterion of structure with notch.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.653-659
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• 1989

Elastic-plastic fracture toughness J$_{IC}$ can be used as an effective design criterion in elastic plastic fracture mechanics. In the J$_{IC}$ test methods approved by ASTM and JSME, there are discrepancies such as the definition of J$_{IC}$, the slope of the blunting line, curve fitting method and the measurement of crack extension etc. The objective of this paper is to evaluate the effect of these discrepancies on the determination of J$_{IC}$ values. Fracture toughness tests were performed on A516, SA508 and SCM415 steels, and test results were analyzed according to ASTM E 813-81, ASTM E 813-87 and JSME S 001-1981. Results showed significant differences depending on the analysis methods. Therefore, a conversion equation between two ASTM methods was proposed, and the conversion error was within acceptable range(less then 8.5%)en 8.5%)

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.2
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• pp.143-152
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• 2006

High performance concrete(HPC) has been widely used in high-rise building. The HPC has several benefits including high strength, high fluidity and high durability. However, spalling is susceptible to occur in HPC and HPC also tends to be deteriorated in the side of fire resistance performance at fire. This paper investigated the spalling prevention of high performance RC column. Control concrete showed severe failure and a case of concrete with fire enduring spraying material exhibited more severe spalling failure than even control concrete. In addition, concrete with fire enduring paint reported the most favorable spalling resistance effect for preventing spall, compared with other concrete covered with finishing materials, such as fire enduring spraying material, gypsum board, marble board and fire enduring PC board. Meanwhile, concrete adding 0.1% of PP fiber demonstrated spalling resistance performance after 3hours load bearing test.

• Journal of the Korea Institute of Building Construction
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• v.11 no.5
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• pp.419-425
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• 2011

Topping concrete that is not reinforced with rebar to prevent poor tensile performance is vulnerable to cracking. In this study, jute, which is known to be an excellent natural fiber material for strengthening concrete performance, was compared with other cellulose fibers in terms of its capacity to reduce the cracking of concrete. As a result, it was found that compared with concrete using other fibers, concrete using jute fiber showed more than a 50 % reduction of plastic shrinkage crack resistance with the contents of 0.9 kg/$m^3$ and 1.2 kg/$m^3$ for. For impact strength tests, the final destruction of WF and PULP fibers took up to 5 times the number of falls, while jute has 10-18 circuitry, showing excellent ductility properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.839-842
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC-ZrB$_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_2$O$_3$+Y$_2$O$_3$. Phase analysis of composites by XRD revelled $\alpha$ -SiC(6H), ZrB$_2$, and YAG(Al$_{5}$ Y$_3$O$_{12}$ ). Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism, the fracture toughness showed the highest value of 6.3MPa.m$^{1}$2/ for composites added with 24wt% $Al_2$O$_3$+Y$_2$O$_3$additives at room temperature. The resistance temperature coefficient respectively showed the value of 2.46$\times$10$^{-3}$ , 2.47$\times$10$^{-3}$ , 2.52$\times$ 10$^{-3}$ $^{\circ}C$ for composite added with 16, 20, 24wt% A1$_2$O$_3$+Y$_2$O$_3$additives. The electircal resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to 90$0^{\circ}C$.