• Proceedings of the KWS Conference
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• 2009.11a
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• pp.57-57
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• 2009

산업의 고도화에 따른 구조물의 사용 환경이 열악해지고 최근 에너지저감과 환경문제 개선을 위한 경화의 요구에 따라 뛰어난 내식성 및 우수한 고비강도 특성을 갖고 있는 타이타늄 및 타이타늄합금의 활용에 대한 연구가 많은 주목을 받고 있다. 이에 따라 타이타늄 신합금의 개발뿐만 아니라 기존에 개발되어 비교적 보편적으로 적용되고 있는 타이타늄 부품의 제조 및 성형기술에 대한 수요도 급증하고 있다. 특히, 기기 및 부품 제조를 위한 용접/접합기술도 매우 중요한 요소기술로 자리메김하고 있다. 타이타늄은 산소, 수소 등의 침입형 원소와의 친화력이 강한 활성이 큰 금속으로 용접시 고온에 노출되면 급격히 산화 및 취화 등의 문제를 발생한다. 따라서 타이타늄의 용접시에는 $426^{\circ}C$이상의 온도에서는 대기로부터 용접부가 차단되도록 하는 쉴딩기술이 매우 중요하다. 타이타늄의 용접은 일반적으로 아크용접, 전자빔 용접, 레이저 용접 및 확산접합 등이 적용되고 있으나 용접입열 조정이 용이하고 아크 안정성이 높고 용접부의 기계적 특성이 우수한 GTA 용접이 작업성을 고려하여 가장 많이 적용되고 있다. 본 연구에서는 미국용접학회(AWS)의 타이타늄 용접가이드를 분석 및 소개하였고, 1t 이하의 박판 CP Ti를 대상으로 GTAW 용접부 미세조직 및 기계적 특성을 분석하였다. 이때, 용접 비드폭 제어 및 펄스 용접기술을 통하여 박판 타이타늄의 최적 GTAW 공정변수 제어기술을 분석하였다.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.23 no.2
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• pp.323-332
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• 1993

저자는 1988년 6월 1일부터 1993년 6월 30일까지 서울대학교병원 치과진료부에 내원하여, 병리조직학적으로 확인된 구강악안면부 악성종양환자 35명의 방사선사진 소견과 자기공명영상 소견을 비교하여 다음과 같은 결론을 얻었다. 1. 일반적인 방사선사진소견으로는 미만성의 골파괴가 15례 (42.9%), 연조직종괴의 음영이 7례 (20,0%), 부유치를 보인 경우가 3례 (8.6%), 골경화가 2례 (51.7%)로 나타났다. 2. 자기공명영상 소견은 연조직종괴가 23례 (65.7%), 골수침범이 12례(34.5%), 피질골 파괴가 14례(40.0%), 정상피질골에 골수침범이 1례 (2.9%), 지방층소실이 19례(54.3%), 림파절전이가 8례 (22.9%), 조영증강이 15례 (42.9%), 골증식이 1례 (2.9%)였다. 3. 구강악안면부의 악성종양환자에 있어서, 방사선사진에서 관찰하기 힘들었던, 종양의 구강저, 저작근, 부인두강, 사골동, 측두하와, 악하선, 비강 등 인접조직으로의 침범여부 및 골파괴 정도와 림파절전이를 평가하는 데 자기공명영상은 도움을 주었다. 4. 정진율은, 방사선사진에서 35례중 16례로 45.7%였고, 자기공명영상에서는 35례중 27례로 77.1%로 자기공명영상의 정진율이 더 높았으나, 일반적인 방사선사진이 자기공명영상보다 더 우세한 경우도 2례 있었다.

• Composites Research
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• v.36 no.1
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• pp.25-31
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• 2023

Composite structures have been designed by stacking the laminae with different stacking angles to meet the required mechanical performance. Although the induced stresses on the composite structures under the external loads usually differ depending on the location, we determined the stacking sequence based on the maximum stress, which leads to low efficiency and generally is not the optimum design. Recently, piecewise integrated composites (PICs) were suggested for solving this inefficiency. PICs assume the perfect bonding between adjacent pieces, but this is ideal and hard to accomplish. Therefore, the overlap at the boundary is essential to prevent separation from each other. In this study, we investigated the effect of the overlap design on the impact failure mode of PIC plates. We fabricated the sample composite plates with different overlap designs using the fast curing carbon prepreg and conducted the impact tests according to ASTM D 7136. We found that PICs had different failure modes according to the overlap design, which lead the changes of absorbed impact energies as well as impact load curves.

• The Korea Journal of Herbology
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• v.24 no.4
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• pp.49-53
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• 2009

Objectives : The protective effect of Vasopurus, a mixture of three medicinal plants, on atherosclerosis induced by dietary cholesterol in low density lipid (LDL) receptor deficient mice was studied. Methods : Experimental groups were divided into three groups of six animals each; a normal group (N); a high cholesterol group (HC), a high cholesterol plus Vasopurus group (HCVA). The experimental groups were fed for 6 months. Results : Vasopurus supplementation significantly lowered plasma total cholesterol and LDL cholesterol conc entrations compared with the high.cholesterol (HC) diet group. In addition, supplementation with Vasopurus significantly increased fecal cholesterol contents compared to mice fed a HC diet. Mice whose diet was supplemented by Vasopurus showed considerably fewer atherosclerotic plagues in the aortic values of heart and aortas compared to mice receiving the HC diet. Conclusions : These results indicate that Vasopurus has efficacy in anti.atherosclerosis medication.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.327-335
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• 2009

In the seismic region, non-ductile structures often form soft story and exhibit brittle collapse. However, structure demolition and new structure construction strategies have serious problems, as construction waste, environmental pollution and popular complain. And these methods can be uneconomical. Therefore, to satisfy seismic performance, so many seismic retrofit methods have been investigated. There are some retrofit methods as infill walls, steel brace, continuous walls, buttress, wing walls, jacketing of column or beam. Among them, the infilled frames exhibit complex behavior as follows: flexible frames experiment large deflection and rotations at the joints, and infilled shear walls fail mainly in shear at relatively small displacements. Therefore, the combined action of the composite system differs significantly from that of the frame or wall alone. Purpose of research is evaluation on the seismic performance of infill walls, and improvement concept of this paper is use of SHCCs (strain-hardening cementitious composites) to absorb damage energy effectively. The experimental investigation consisted of cyclic loading tests on 1/3-scale models of infill walls. The experimental results, as expected, show that the multiple crack pattern, strength, and energy dissipation capacity are superior for SHCC infill wall due to bridging of fibers and stress redistribution in cement matrix.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.53-62
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• 1987

High power lasers provide a controllable and precise energy source in surface transformation hardening. A careful control of the process is needed in order that the surface layer of the material reaches the austenizing temperature, but that it does not melt. In order to achieve this the results of theoretical and experimental studies on the laser surface hardening of a medium carbon steel are described. A two-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and heat treatment, was established on the basis of the finite element method. For the confirmation of the accuracy of the numerical analysis, a medium carbon steel (SM 45C) of 5mm thickness was heat-treated with a 1kW CW CO$_{2}$ laser machine, while the traverse speed and the distance from the focal point (defocused distance) were varied. Experimental and numerical results showed a similar tendency in correlations between the hardened zone shape and the process parameters. With increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. Too small beam spot diameters are to be avoided, since the surface melting would lower the surface hardness and produce an uneven surface which may be unacceptable because of the possible requirement for subsequent machining. It could be observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produce a large width of the hardened zone but no melting on the surface.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.3-14
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• 2012

This paper describes experimental results on the seismic performance of SHCC (strain-hardening cement composite) infill wall for improving damage tolerance capacity of non-ductile frame. To investigate the effect of tensile strain capacity and cracking behavior of SHCC materials on the shear behavior of SHCC infill wall, three infill walls were fabricated and tested under cyclic loading. The test parameter in this study is a type of cement composites; concrete and SHCCs. The two types of SHCC materials were prepared for infill walls. In order to induce crack damages into the mid-span of the infill wall, each infill wall had two 100-mm-deep-notches on both sides. Test results indicated that SHCC infill walls showed superior crack control capacities and much larger drift ratios at the peak loads than RC (reinforced concrete) infill wall, as expected. In particular, due to the bridging actions of the reinforcing fibers, SHCC matrix used in this study would delay the stiffness degradation of infill wall after the first inclined cracking. Moreover, from the damage classes based on the cracks' maximum width in the infill walls, it was observed that PIW-SHD specimen possessed nearly threefold seismic capacities compared to PIW-SLD specimen. Also, from the results on the strain of diagonal reinforcements, it can be concluded that the SHCC matrix would resist a part of tensile stresses transferred along steel rebar in the infill wall.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.310-315
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• 2017

Automotive waterproof connectors are highly functional parts that must be air-tight in a complex environment. In the LSR multi-cavity injection molding process for manufacturing waterproof connectors, it is important to maintain a uniform curing temperature between the cavities in order to obtain a quality product. For this purpose, we designed the capacity of the cartridge heater differently for each position, and then linked the heat transfer analysis and optimization module to obtain the optimal cartridge heater capacity. As a result of the optimization analysis, the temperature deviation between cavities was decreased from $13.1^{\circ}C$ to $8.1^{\circ}C$ compared with the case in which constant heater capacity was applied, so that the design criterion could be satisfied within a temperature deviation of $10^{\circ}C$ for uniform curing. This study suggests that this method can be applied efficiently to the design of a large area multi-cavity LSR mold heater.

• Korean Journal of Agricultural Science
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• v.6 no.2
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• pp.185-191
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• 1979

Compressive and tensile strengths of commonly being used mortar and mortar specially hardened by adding 1%, 2% and 3% of $CaCl_2$ were compared under the different mixing ratio of mortar and ages to investigate the effect of $CaCl_2$ which is being used as a promotor for coagulation and hardness, on the strength of mortar. The results obtained were as follows: 1. The compressive strength of mortar hardened by addition of $CaCl_2$ was higher than that of commonly being used mortar. The highest compressive strength of mortar was obtained when 2% of $CaCl_2$ were added. 2. The tensile strength of mortar, which was made by adding $CaCl_2$ and aged for seven days, was higher than that of commonly being used mortar. The highest tensile strength of mortar was obtained when 1% of $CaCl_2$ was added and aged for 28 days. And the tensile strength of mortar with 2% of $CaCl_2$ was lower than that of commonly being used mortar. 3. When the amount of $CaCl_2$ added was higher than 3%, the mortar was abruptly hardened and thereby occurred crack was considered lowering strength of mortar. 4. The rich mix was effective for the increasing the compressive and tensile strength before seven days of age and less effective after seven days of age. Therefore, the addition of one to two per cent of $CaCl_2$ would be effective for promoting initial strength of mortar during winter season.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.405-413
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• 2020

The normal stress of cement paste measured under squeeze flow is divided into an elastic solid region at strains between 0.0003 and 0.003 and a strain-hardening region at strains of 0.003 and 0.8. A modeling equation at the strain-hardening region was proposed. First, from the viewpoint of fluid behavior, the power-law non-Newtonian fluid model, with a power-law consistency (m) of 700 and a power index (n) of 0.2, was applied. The results showed good agreement with the experimental results except for an elastic solid region. Second, from the viewpoint of ductile yielding solid behavior, the force balance model was applied, and the friction coefficient between the sensor part measuring the load and the surface of the cement paste was derived as a polynomial of the normal strain by applying the half-interval search method to the experimental data. The results showed good agreement with the experimental results only in the middle normal strain region at strains between 0.003 and 0.3. The rheological behavior of the cement paste under squeeze flow was more consistent with the experimental results from the viewpoint of power-law non-Newtonian fluid behavior than from the viewpoint of ductile yielding solid behavior in the strain-hardening region.