• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.157-160
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• 2004

If concrete structure is exposed to high temperature such as long-term fire, damages affecting partial or whole structure system may occur. Therefore accurate diagnosis of deterioration is needed based on mechanism of fire deterioration in general concrete structures. Fundamental information and data on the properties of concrete exposed to high temperature are necessary. Especially, the amount of fire damage done to concrete depends on the materials, the standard design compressive strength of concrete, and heated temperature. So, the object of this study is to present data for supposed heated Temperature of deteriorated concrete by fire.

• 한국기계연구소 소보
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• s.20
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• pp.79-87
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• 1990

Advanced ceramics have some excellent properties as the material for the mechanical component. It is, however, very difficult to grind ceramics with high efficiency because of their high strength, hardness and brittleness. Thus it is required also by a strong boom of demands for development of Machinable ceramics with high machinability in the most of industries. In present research, experiments are carried out to compare the machinability of sample Machinable ceramics. A $\ell$N(Aluminum Nitride) with additives of BN(Boron Nitride), yttrium. CaO are turned with cut-off tool type tungsten carbide bite using conventional turning machine.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.535-539
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• 2004

Although magnesium has high potential for structural material due to the lightweight and high specific strength, the structural application has been limited by the low ductility at room temperature. The reason of the poor ductility is few activated slip systems of magnesium (HCP structure) during deformation. As temperature increases, however, additional non-basal slip systems are incorporated to exhibit higher ductility comparable to aluminum. In the present study, a series of tensile tests of Mg-Al alloy has been carried out to study deformation behavior with temperature variation. Analysis of load relaxation test results based on internal variable approach gave information about relationship between the micromechanical character and corresponding deformation behavior of magnesium. Especially, the material parameter, p representing dislocation permeability through barriers was altered from 0.1 to 0.15 as the non-basal slip systems were activated at high temperature.

• Journal of the Korean Society of Mechanical Technology
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• v.20 no.6
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• pp.941-946
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• 2018

Currently, due to the development of technology, the industry is proceeding with the development of advanced materials with high performance such as light weight, heat resistance and electric conductivity. Carbon Fiber Reinforced Plastics (CFRP) is an excellent material with high heat resistance, high strength and thermal shock resistance. In order to obtain excellent hole shape in CFRP drilling, we compared the modified drill shape and the conventional carbide drill. On the other hand, we determine the proper helix angle by observing the CFRP surface according to the helix angle at the trimming of the end mill proceeding after the hole machining.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.39-50
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• 1999

The physicochemical, mineralogical, hydraulic, swelling and mechanical properties of a domestic bentonite for use as the buffer material in a high-level waste repository have been measured. The bentonite is identified to be a Ca-bentonite, and the hydraulic conductivity of the compacted bentonite with the dry density higher than 1.4 Mg/㎥ is lower than 10$^{-11}$ m/s When the dry densities are 1.4 to 1.8 Mg/㎥, the swelling pressures are in the range of 6.6 to 143.5 kg/$\textrm{cm}^2$. The unconfined compressive strength is about 94 kg/$\textrm{cm}^2$, and the coefficient of volume change and the coefficient of consolidation are in the range of 0.O0249 to 0.02142 $m^2$/MN and 0.018 to 0.115$m^2$/year, respectively.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1028-1034
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• 2001

The 2.5 vol% TiNi/6061Al composites were fabricated by permanent mold casting. The microstructures and tensile test for the cold rolled composites with maximum 50% reduction ratio were investigated. In the case of TiNi fiber with 2mm interval in preform, the interface bonding of fabricated composites were good, interface diffusion layer of this composites was made by the mutual diffusion. Transverse section of TiNi fiber was decreased with increasing reduction ratio and longitudinal section of TiNi fiber showed multiple wave phenomenon. And the tensile strength of composites at 38% reduction ratio was the most high. In the case of over 38% reduction ratio, the decrease of the tensile strength was due to TiNi fiber rupture by excess working. The fracture mode was appeared brittle fracture with increasing reduction ratio.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.319-324
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• 2012

The hot-stamping technique is a forming method for manufacturing high-strength parts, in which the part is cooled rapidly after press forming above the austenite transformation temperature. Boron steel, which contains a very small amount of boron, is one of the materials used for hot stamping. The purpose of this study is to investigate the microstructure and mechanical properties according to the heat-treatment conditions. Die-quenching from various temperatures was conducted for different elapsed heat-treatment times. Laser-welded boron steel after quenching has a tensile strength of 1454 MPa and an elongation of 6 %. It has 94 % of the tensile strength of the base metal (1522 MPa). These properties can provide practical information for the use of boron steels for hot stamping.

• Journal of Technologic Dentistry
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• v.34 no.2
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• pp.75-81
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• 2012

Purpose: All ceramic crown, made from zirconia instead of metal for core material, is recognized the best esthetical prosthesis. Recently, high-priced zirconia blocks and expensive CAD/CAM machines come into use for making zirconia core. In this study, slip casting process is adapted to evaluate the possibility of the recycling the remained parts of zirconia block after machining. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Passed powders were ball milled under various conditions to obtain the optimum zirconia slip for casting. Solid casting method was used for casting the specimens with plaster mold. Formed specimens were dried and biscuit fired at $1,000^{\circ}C$ for 1 hour. Biscuit fired specimens were finished with exact shape of square pillar. Finished specimens were fired from $1,200^{\circ}C$ to $1,550^{\circ}C$ at $50^{\circ}C$ intervals for 1 hour. Linear shrinkage, apparent porosity, water absorption, bulk density, and flexural strength were tested. Microstructures were observed by SEM. Results: Above examinations indicated that the optimum firing temperture was $1,500^{\circ}C$, and when fired at this temperature for 1 hour, apparent porosity was 0% and flexural strength was 680MPa. SEM photomicrographs showed uniform 200~300nm grain size, which is equal with microcture of sintered commercial zirconia block. when compare 24% linear shrinkage of cast specimen with 20% linear shrinkage of CAD/CAM machined block, it was estimated that the size controlling of cast core was not so difficult. Conclusion: According to the all of this experimental results, the cast zirconia core produced from the remained parts of zirconia block was possible to use for all ceramic denture.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.5
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• pp.1-7
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• 2008

A study of new materials that are light-weight, high in strength has become vital to the machinery of auto industries. But then, there are a lot of problems with developing such materials that require expensive tools, and a great deal of time and effort. Therefore, the improvement of fatigue strength and fatigue life are mainly focused on by adopting residual stress. And Influence of corrosive condition for corrosion fatigue crack was investigated, after immersing in 3.5%NaCl, $10%HNO_3$+3.5%HF, $6%FeCl_3$. The immersion period was performed for 365days. The compressive residual stress was imposed on the surface according to each shot velocity based on shot peening, which is the method of improving fatigue life and strength. Fatigue life shows more improvement in the shot peened material than in the un peened material in corrosion conditions. The threshold stress intensity factor range was decreased in corrosion environments over ambient. Compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation. The fatigue crack growth rate of the Shot-peened material was lower than that of the un peened material. Also m, fatigue crack growth exponent and number of cycle of the shot peened material was higher than that of the un peened material. That is concluded from effect of da/dN.

• Journal of the Korean Ceramic Society
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• v.39 no.12
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• pp.1133-1137
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• 2002

The cement for solidification of the toxic waste was fabricated using a mixture of the waste concrete powder and blast furnace slag in the ratio of 1:1 and its hydrate morphology and compressive strength of the sample were evaluated in order to apply to the solidification of the COREX sludge. The X-ray diffraction analysis of the sample which prepared by the addition of 10% Portland cement and hemihydrate showed the presence of $Ca(OH)_2$, ettringite, gel-phase and C-S-H hydrate. Compressive strength of the sample exhibited enough high to use as a solidification cement. The strength of the sample was over 140 kgf/$m^2$ in 7 days in case of solidification of the COREX sludge and the sample possess sufficient morphology for the solidification and stabilization of the waste sludge.