• 한국주조공학회지
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• 제14권6호
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• pp.566-575
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• 1994

The effects of varying the pouring temperature and the die preheating temperature in producing centrifugally cast HP alloy modified with Nb was evaluated on the basis of the resultant macrostructure, microstructure and hardness of these castings. Increased die preheating temperatures and pouring temperatures resulted in an increase in the thickness of the columnar dendritic zone, the primary and secondary dendrite arm spacing and the thickness of the zone of porosity at the casting I.D.(inner diameter). Lower die preheating temperature and pouring temperatures result in increased grain fineness and an increased zone of equiaxed grains. A higher hardness was achieved toward the casting O.D.(outer diameter) compared to the casting I.D., attributable to alloy segregation toward the casting I.D. and segregation differences resulting from reduced solidification cooling rates toward the casting I.D. Also, a higher hardness was realized at the cold end of the casting attributed to a more uniform distribution of carbides.

• 한국결정성장학회지
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• 제13권1호
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• pp.1-4
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• 2003

In the present work we consider morphological structure of the faces of BGO crystals grown by Czochralski technique under the conditions of low temperature gradient (0.1~1 deg/cm) and interconnection between the morphological features of faces at the crystallization front and the formation of defects within the crystal volume. It is demonstrated that the {112} faces retain stability while the growing surface deviates from the crystallographic (112) plane up to 1 degree. At larger deviation, the region of the stable facet growth passes either to the region of macrosteps or to the region of normal growth. depending on conditions.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.390-395
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• 2002

The experimental and numerical study has been conducted on the sleeve repair welding of API 5L X65 pipeline. SMA W and GTAW were applied to weld the sleeve. The macrostructure and hardness of repair welds have been examined. The [mite element analysis of the multi-pass sleeve-fillet welding has been conducted to validate the experiment and investigate the effects of in-service welding conditions. The effect of gas flow rate on the hydrogen cracking was investigated. The effect of internal pressure on residual stresses and plastic strain was investigated. The allowable heat input was predicted considering the maximum temperature of inner surface of pipe and cooling rate at CGHAZ.

• 한국세라믹학회지
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• 제34권11호
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• pp.1139-1150
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• 1997

A model for predicting the relative density and the compressive strength of open-cell ceramics with three-dimensional network structure was proposed through the interpretation of their macrostructure and fracture mechanics. The equation predicting the relative density was derived under the assumption that the open-cell structure was a periodic array of the tetrakaidecahedron unit cell consisting of cylindrical struts containing the internal hollow with the shape of a triangular prism. The model for compressive strength of open-cell ceramics with the hollow strut was also developed by modifying conventional model which based on fracture behavior of them subjected to the compressive stress. Both the relative density and the compressive strength were expressed in terms of the ratio of the strut diameter to the length together with the ratio of the hollow size to the strut diameter. The proposed model for the relative density and the compressive strength of the alumina-zirconia composite with open-cell structure were accorded well with the experimental values, whereas Gibson-Ashby and Zhang's model did not show such a good agreement.

• Journal of Welding and Joining
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• 제20권4호
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• pp.534-537
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• 2002

In the various industry such as shipbuilding and automobile, etc., Al-alloys are used to reduce weight and improve economical efficiency, and they are mainly utilized in the process of Friction Stir Welding (FSW). A number of studies have been carried out on the metallurgical characteristics of friction stir welding In Al-alloys. However, research on the thermal behavior of FSW by using numerical analysis is not sufficient in the domestic and abroad. In this paper, therefore, numerical simulation was used to find out thermal behaviour of FSW by finite element method. We considered heat source that occurred by friction between tool shoulder including pin and base metal. To confirm the result of simulation, macrostructure is examined and compared after welding. The result of numerical simulation shows that Al-alloy is welded under a melting point of Al around pin by FSW.

• 한국주조공학회지
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• 제5권3호
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• pp.19-26
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• 1985

This study has been carried out to examine into wettability of Cu-5%Sn alloy in $Al_2O_3$, MgO, $SiO_2$ and graphite, respectively and investigated into the change in macrostructure of Cu-5%Sn alloy according to kind and mixing rate of mold-coating. The results obtained from the experiment are summerized as follows; 1. Cu Cu-5%Sn alloy, wettabilities of $Al_2O_3$ and MgO were good, on the other hand, wettabilities of $SiO_2$ and graphite were bad. 2. The fine equiaxed zone was created because of the role of $Al_2O_3$ and MgO as preferential nucleation sites. 3. Notwithstanding change of mixing rate of $SiO_2$ in mold coating the equixed zone was not created. 4. The area of equiaxed zone was varied according to mixing rate in the case of using $Al_2O_3$ and MgO in mold-coating.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(B)
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• pp.172-174
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• 2012

요구사항은 소프트웨어 아키텍처 설계의 핵심 요소로서, 아키텍처의 구축과 생성의 근거를 제시해준다. 이러한 요구사항 분석을 위해 다양한 요구사항 분석 방법이 제안되고 있는데 그 중 대표적인 기법은 시나리오 기반의 분석, 목표 기반의 분석, 시나리오를 이용한 목표기반의 분석이다. 그러나 이러한 요구사항 분석 방법들은 정형화되어 있지 않아 요구사항을 분석하는 아키텍트에 의존할 수밖에 없다. 따라서 본 논문에서는 텍스트학을 기반으로 정형화된 기법인 거시구조를 이용한 요구사항 분석 방법을 기반으로 요구사항 분석 프로세스를 개선하여 제안하였다. 기존 연구에서 제안한 거시구조 요구사항 분석 방법을 재해석하여 요구사항을 분석하는 단계를 나누고 각 단계의 시스템 요소 설계와 구조를 정의하여 요구사항 분석 프로세스의 설계를 수행하였다.

• International Journal of Korean Welding Society
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• 제2권2호
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• pp.36-41
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• 2002

The experimental and numerical study has been conducted on the sleeve repair welding of API 5L X65 pipeline. SMAW and GTAW were applied to weld the sleeve. The macrostructure and hardness of repair welds have been examined. The finite element analysis of the multi-pass sleeve-fillet welding has been conducted to validate the experiment and investigate the effects of in-service welding conditions. The effect of gas flow rate on the hydrogen cracking was investigated. The effect of internal pressure on residual stresses and plastic strain was investigated. The allowable heat input was predicted considering the maximum temperature of inner surface of pipe and cooling rate at CGHAZ.

• Journal of Welding and Joining
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• 제14권5호
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• pp.49-58
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• 1996

In Korea Gas Corporation, as one of the pipeline repairing methods, damaged pipelines are sometimes treated with a temporally employment of split sleeve. On conducting the repair process, circumferential fillet and longitudinal groove welding usually must be included. For the case of groove welding, a considerable amount of R&D have been carried out related to property changes, while few study on the property change in fillet welding has been conducted. In this paper, so as to confirm the specification of fillet welding in terms of safety and reliability, properties changed by fillet welding were investigated for two welding processes. Qualifying tests such as reviewing macrostructure and nick-break tests were performed according to API 1104 and ASME section IX. In addition, tensile properties and hardness were evaluated according to KS B0841 and BS 4515. The fillet weld prepared by the qualified procedure showed melting depth of 0.8∼1.3mm and heat affected zone of 2.8∼3.4mm length. No crack and lack of penetration were observed. And the results of hardness and nick-break tests satisfied code requirements. The area crossed by fillet and groove welding line was found to have minimal tensile strength.

• 열처리공학회지
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• 제20권5호
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• pp.231-236
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• 2007

High velocity oxy-fuel (HVOF) spraying was used to coat Ti(Al,O)/$Al_2O_3$ powder onto the SS41 steel plate. Macrostructure of the coated specimen has been investigated by scanning electron micrograph (SEM). High temperature oxidation behavior of the coated specimen and SS41 steel have been studied. From the results of SEM observation, Ti(Al,O)/$Al_2O_3$ powder was coated well onto the substrate SS41 steel. Porosity onto the coated layer was only 0.38%. The oxidation results showed that Ti(Al,O)/$Al_2O_3$ powder coated SS41 steel have improved little oxidation resistance at $900^{\circ}C$ in air, but improved remarkably oxidation resistance at $800^{\circ}C $ in air compare to the substrate SS41 steel.