• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.520-523
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• 2002

The o]d technique of sandblasting which has been used for paint or scale removing, deburring, and glass decorating has recently been developed into a powder blasting technique for brittle materials, capable of producing micro structures larger than $100\mu\textrm{m}$. In this study, we investigated the effect of the size of abrasive and the stand-off distance on the machinability of SUS 304. The varying parameters were the impact angle $90^{\circ}$, scanning times of nozzle 10 and the different nozzle height between 70mm and 140mm. The diameter of dot pattern were 0.2mm. The powder were alumina sharp particles, WA #600, #800 and #2000. The blasting pressure of powder at 0.3 Mpa.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.7-20
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• 2016

A brief overview is given of the development of various structural steels and their welding application technology. Firstly, the general characteristics and welding performance of structural steels used in architecture and bridge are introduced. For safety against earthquakes or strong wind, and for highly efficient welding in high-rise building constructions, ultra high strength steel with tensile strength over 800 MPa or high HAZ toughness steel plates under high heat input welding have been developed. In particular, efficient welding technology ensuring high resistance to cold and hot cracking of ultra high strength steel is reviewed in the present paper. Secondly, various coated steels used mainly for outer part in construction are briefly discussed. Moreover, a major drawback of coated steel during welding operation, and several solutions to overcome such technical problem are proposed. It is hoped that this review paper can lead to significant academic contributions and provide readers interested in the structural steels with useful welding technology.

• Journal of Power Electronics
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• v.9 no.5
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• pp.800-808
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• 2009

This paper presents a practical method of pressure control for a hydraulic oil-pump system using an SR (Switched Reluctance) drive. For a 6Mpa grade hydraulic oil-pump, a 2.6kW SR drive is developed. In order to get high performance pressure dynamics in actual applications, a data based PID control scheme is proposed. The look-up table from a pre-measured data base produces an approximate current reference based on motor speed and oil-pressure. A PID controller can compensate for the pressure error. With the combination of the two references, the proposed control scheme can achieve fast dynamics and stable operation. Furthermore, a suitable current controller considering the nonlinear characteristics of an SRM (Switched Reluctance Motor) and practical test methods for data measuring are presented. The proposed control scheme is verified by experimental tests.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.170-173
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• 2006

The purpose of this study is to investigate the effect of post-fire-curing on the strength recovery of fire-damaged concrete The 170 specimens have been tested with variables of concrete strengths(20, 30, 40, 50, 60Mpa) exposed to elevated temperatures till $600^{\circ}C$ and $800^{\circ}C$. After natural cooling, the specimens were subjected to post-fire-curing in water and in a controlled chamber for a total duration of 56days. Unstressed compressive strength was conducted to examine the change in the concrete. The test results indicated that the post-fire-curing results in substantial strength recovery and its extent depend on the method and duration of recuring.

• Journal of the Korean Ceramic Society
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• v.27 no.3
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• pp.394-400
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• 1990

Mullite and cordierite were prepared by the sol-gel route. Boehmite, fumed silica and Mg(NO3)2$.$6H2O were their starting materials. Mullite and cordierite powder were mixed by various weight percent. These mixed sols were ball-milled for 48hrs, dried at 100$^{\circ}C$, pressed, cold isostatic pressed and sintered at 1490$^{\circ}C$ for 2hrs. Mullite-cordierite composites sintered at 1490$^{\circ}C$ for 2hrs had>98% of theoretical density. Bending strength of the sintered bodies were 329-249MPa, dielectric constant 7.1-6.7 at 1MHz and thermal expansion coefficient at 800$^{\circ}C$ was matched with Si in the range of 30-35wt% cordierite.

• Journal of the Korean Ceramic Society
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• v.56 no.2
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• pp.184-190
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• 2019

To improve resistance in thermal shock of zirconia setter which is frequently and repeatedly exposed to high temperature, high degree of porosity and control of thermal expansion are needed for which the fused CSZ (CaO stabilized zirconia) is used to produce the zirconia setter. In the present study, the effects of sintering temperature, cool down condition, addition of CaO stabilizer, and addition of other additives on phase transition and thermal expansion behavior of the fabrication process of zirconia setter, were examined. The zirconia setter, fabricated with fused CSZ at 1550℃, exhibited 20.4 MPa of flexural strength, 6.8% of absorbance, and 27.9% of apparent porosity. The rapid change in thermal expansion of zirconia setter is observed at temperature around 800℃, and it was reduced by low firing temperature, slowed cooled down, and addition of CaO.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.25-28
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• 2006

This paper dealt with the LPS process for the development of high performance SiC materials, based on the detailed analysis of their microstructure and mechanical properties. The submicron SiC powder was used for the fabrication of LPS-SiC materials. A mixture of $Al_2O_3$ and $Y_2O_3$ particles was also used as a sintering additive in the LPS process. LPS-SiC materials were fabricated at different temperatures, using various additive composition ratio ($Al_2O_3/Y_2O_3$). The total amount of additive materials ($Al_2O_3+Y_2O_3$) was fixed as 10 wt%. The characterization Of LPS-SiC materials was investigated by means of SEM, XRD and three point bending test. The LPS-SiC material represented a relative density of about 98 % and a flexural strength of about 800MPa, when it was fabricated at the temperature of $1820^{\circ}C$ and the additive compositional ratio of 1.5.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.471-477
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• 2003

The floating ring seal is often used in the turbopump (TP) unit of liquid rocket engine (LRE) owing to its inherent ability of minimizing the leakage flow and superior dynamic characteristics as well. This paper describes the test results concerned with the lock-up and dynamic characteristics of the floating ring seals in the turbopump. The characteristics of the floating ring seals were extracted from the frequency response function (FRF) by instrumental variable method. The experiment was tested at 7.0MPa and 0-24,800 rpm. And the test results were introduced about the dynamic characteristics of floating ring seal related with the eccentricity and attitude angle.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1167-1168
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• 2006

In this study, the pure iron powder was treated with aqueous phosphoric acid to produce phosphate insulating layer on the surface. After drying the powder, it was compacted in a mold with a diameter of 20mm at 800MPa. The powder compacts were then heat treated at $500^{\circ}C$ for 1 hour. The results showed that insulated iron powder was obtained with uniform phosphate layer by chemical reaction. With increased amount of phosphate layer, the core loss and density of compacts were decreased. It was also found that the addition of ethyl alcohol during insulating reaction resulted in improved core loss value.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.84.1-84.1
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• 2010

국내에서는 플레이트거더의 휨 강도 및 전단 강도를 허용응력설계법에 기반한 도로교설계기준(2005)에 근거하여 규정하고 있으며, 국외의 경우 하중저항계수설계법에 근간을 둔 AISC(2005) 등의 규정을 통해 산정하고 있다. 최근에는 인장강도 800MPa 급의 강재가 생산되고 있으나 국내 설계기준에서는 아직까지 상기 인장강도를 갖는 고강도강에 대한 설계기준은 마련되지 않고 있다. 본 연구에서는 휨과 전단이 동시에 작용하는 고강도강 적용 플레이트거더의 극한거동 해석을 통해 국내기준의 적용성을 판단하고, 국외기준인 AISC(2005)와 비교하여 나타내어 허용응력설계법에 근거한 국내기준의 강도산정법의 한계점에 대해 고찰하였다.