• 대한치과기공학회지
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• 제30권1호
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• pp.65-71
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• 2008

The use of titanium in the field of dentistry has increased, due to their excellent biocompatibility, appropriate mechanical properties, corrosion-resistance and low price. However, many difficulties with the use of titanium for metal-ceramic crowns remain to be solved. The objective of this study was to evaluate the influence of surface modifications on the bonding characteristics of specific titanium porcelain bonded to cast titanium. The surfaces of Titanium were prepared with 4 test groups, i) sandblasted with particles of different size, ii) sandblasted after treated oxidization and oxidized after sandblast. We observed the bond strength and node aspect of titanium and ceramic, and respect to the methods of modifying surface of titanium by the test of mean roughness of surface, Scanning Electron Microscope, and 3-point flexural bend test. The results show that, 1. The specimens, which treated oxidization after process of sandblast with particles of 50um size, were the better for the bond strength in comparison with other specimen. 2. The specimen with process of sandblasting after oxidization treatment were the better for stability of the bond strength. 3. The wettability of titanium surface affect the bond strength.

• 대한기계학회논문집B
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• 제21권5호
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• pp.615-627
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• 1997

An experiment was performed to local heat transfer coefficient and Nusselt number in the circular duct of 180.deg. bend for Re=6*10$^{4}$, 8*10$^{4}$ and 1*10$^{5}$ at swirling flow and non-swirling flow conditions. The test tube with circular section was made by stainless which has curvature ratio 9.4. The wall of test tube was heated directly by electrical power to 3.51 kw and swirling motion of air was produced by a tangential inlet to the pipe axis at the 180 degree. Measurements of local wall temperatures and bulk mean temperature of air are made at four circumferential positions in the 16 stations. The wall temperatures show particularly reduced distribution curve at bend for non-swirling flow but this effect does not appear for swirling flow. Nusselt number distributions for swirling flow which was calculated from the measured wall and bulk temperatures were higher than that of non-swirling flow. Average Nusselt number of swirling flow increased about 90 ~ 100% than that of non-swirling flow whole through the test tube. The Nu/N $u_{DB}$ values at the station of 90.deg. for non-swirling flow and swirling flow are respectively about 2.5 and 4.8 at Re=6*10$^{4}$. Also that is good agreement with Said's result for non-swirling flow. flow.

• 한국세라믹학회지
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• 제43권7호
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• pp.439-444
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• 2006

Artificial graphite generally manufactured by carbonization sintering of shape-body of kneaded mixture using granular cokes as filler and pitch as binder, going through pitch impregnation process if necessary and finally applying graphitization heat treatment. Graphite materials are used for core internal structural components of the High-Temperature Gas-cooled Reactors (HTGR) because of their excellent heat resistibility and resistance of crack progress. The HTGR has a core consisting of an array of stacked graphite fuel blocks are machined from IG-110, a high-strength, fine-grained isotropic graphite. In this study, crack stabilization and micro-structures were measured by bend strength and fracture toughness of isotropic graphite grade IG-110. It is important to the reactor designer as they may govern the life of the graphite components and hence the life of the reactor. It was resulted crack propagation, bend strength, compressive strength and micro-structures of IG-110 graphite by scanning electron microscope and universal test machine.

• 한국공작기계학회논문집
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• 제16권1호
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• pp.1-8
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• 2007

The present study examined the mechanical properties of the friction welding zone of solid and hollow shafts made with SM20C according to the depth of the notch. Friction welding was conducted at welding conditions of 2,000 rpm, friction pressure of 60MPa, friction time of 1.4 seconds, upset pressure of 100MPa, and upset time of 2.0 seconds. In the tensile strength test, the tensile strength decreased as the depth of the notch increased. Tensile strength was moderately high when the depth of the notch was 2mm. The tensile strength of the welding zone increased as the friction revolution radius increased, because the latter led to the generation of adequate friction heat. According to the hardness test, hardness likewise increased as e friction revolution radius increased. In the bending test, the bend strength of the solid shaft decreased when the depth of the notch was 0-2mm but increased when the latter was 3-5mm. With regard to the hollow shaft, the bend strength drastically decreased when the depth of the notch was 3-4mm. Upon examination it was found that the microstructure became finer when the friction revolution radius increased.

• Advances in concrete construction
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• 제1권4호
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• pp.319-340
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• 2013

This paper presents a comparative study on the double-K fracture parameters of concrete obtained using four existing analytical methods such as Gauss-Chebyshev integral method, simplified Green's function method, weight function method and simplified equivalent cohesive force method. Two specimen geometries: three point bend test and compact tension specimen for sizes 100-500 mm at initial notch length to depth ratios 0.25 and 0.4 are used for the comparative study. The required input parameters for determining the double-K fracture parameters are derived from the developed fictitious crack model. It is found that the cohesive toughness and initial cracking toughness determined using weight function method and simplified equivalent cohesive force method agree well with those obtained using Gauss-Chebyshev integral method whereas these fracture parameters determined using simplified Green's function method deviates more than by 11% and 20% respectively as compared with those obtained using Gauss-Chebyshev integral method. It is also shown that all the fracture parameters related with double-K model are size dependent.

• 한국방재학회 논문집
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• 제10권5호
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• pp.125-133
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• 2010

일반적으로 사행하천의 만곡부에서는 홍수시 월류의 위험성이 높을 뿐만 아니라, 국부적으로 집중되는 흐름분포는 제방의 안정성을 위협한다. 따라서 본 연구는 두 개의 다른 실험수로에 대한 CCHE2D모형의 적용성 검토와 급변만곡의 형태를 갖는 자연하천의 흐름특성분석을 수행하는데 그 목적이 있다. 모의결과 실험에 대한 수위의 백분율 오차는 4.9%이내였으며, 실측치와 근사한 유속분포를 보였다. 실험수로를 통하여 보정된 모형을 이용하여 용담댐 하류 대유리에 위치한 만곡부를 대상으로 흐름특성 분석을 수행하였다. 모의결과는 만곡부의 지형에 의한 영향을 고려하지 못하는 HEC-RAS모형에 비하여 상류부에서 수위가 1.5 m 정도 높게 나타났다. 그러나 모의결과를 기존의 경험식과 비교한 결과 CCHE2D모형이 편수위 모의에 적합함을 알 수 있었으며, 자연하천의 홍수위와 유속산정에도 적합함을 확인할 수 있었다.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.11-19
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• 2010

The performance of the crossover system of a centrifugal compressor stage consisting of static components of $180^{\circ}$ U-bend, return channel vanes and exit ducting with a $90^{\circ}$ bend is investigated. This study is confined to the assessment of performance of the crossover system by varying the shape of the return channel vanes. For this purpose two different types of Return Channel Vanes (RCV1 and RCV2) were experimentally investigated. The performance of the crossover system is discussed in terms of total pressure loss coefficient, static pressure recovery coefficient and vane surface pressure distribution. The experimentation was carried out on a test setup in which static swirl vanes were used to simulate the flow at the exit of an actual centrifugal compressor impeller with a design flow coefficient of 0.053. The swirl vanes are connected to a mechanism with which the flow angle at the inlet of U-bend could be altered. The measurements were taken at five different operating conditions varying from 70% to 120% of design flow rate. On an overall assessment RCV1 is found to give better performance in comparison to RCV2 for different U-bend inlet flow angles. The performance of RCV2 was verified using numerical studies with the help of a CFD Code. Three dimensional sector models were used for simulating the flow through the crossover system. The turbulence was predicted with standard k-$\varepsilon$, 2-equation model. The iso-Mach contour plots on different planes and development of secondary flows were visualized through this study.

• 대한치과교정학회지
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• 제34권1호
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• pp.33-45
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• 2004

제 1소구치가 발치된 증례에서 bull loop를 견치 직후방에 제작한 후 gable bend를 어느 정도 부여할 때 전치부의 효과적인 치축조절과 후방 이동량을 극대화 할 수 있는지를 입체적으로 확인하는 것이 본 연구의 목적이다. 제 1소구치가 제거된 상악우측 인공 치조골부에 중절치부터 제 2대구치까지 실험용 치아들을 식립하였다. 그 후 bull-loop가 형성된 반쪽 호선에 $10^{\circ},\;20^{\circ},\;30^{\circ}$의 gable bend를 부여한 후 3전치를 후방 견인하여 발치공간을 폐쇄시켰고 이러한 실험과정을 각 군마다 3회씩 반복 실험하였다. 발치공간이 폐쇄된 후 실험전, 후의 교합방사선 사진상에 촬영된 전치부와 구치부의 시상면과 교합면 상에서의 각 군별 치아이동 양상을 일요인 분산분석(ANOVA)과 Scheffe 검정으로 평가한 결과 아래와 같은 결론을 얻었다. 1. Gable bend의 양이 증가할수록 전치부의 치축은 치체이동 양상을 보였으며 후방 이동량도 증가하였다. 2. Gablebend의 양이 증가할수록 구치부의 전방 이동량은 감소하였으나 수직적 압하량 및 협측 이동량은 증가하였다(p<0.001). 3. 발치공간에 인접한 견치의 원심회전과 제 2소구치의 근심회전에 의해 악궁의 조화가 이루어졌다(p<0.001).

• 대한기계학회논문집A
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• 제40권3호
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• pp.245-252
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• 2016

본 논문은 벤드(bend)부의 노후 문제를 경감시키기 위한 대안으로 폼패드를 없앤 이중보온관의 형상 설계를 제안하였다. 전 관경에 대해 유한요소해석을 수행하였으며, 이를 토대로 전단제어링 형상을 결정하였다. 제안된 전단제어링 사양 강화이형관에 대한 현장 시공 시험은 진행하였으며, 온도와 응력 데이터를 취득 및 분석하였다. 강화이형관의 제작과 현장 시범시공을 통하여 강화이형관이 폼패드를 시공하지 않으면서도 강관의 열응력이 허용치 기준내에 있음을 확인하였다. 특히 보온재의 전단강도가 강화되어 폼패드를 적용한 기존 벤드보다 낮은 최대 전단응력이 발생함을 확인함으로써, 강화이형관 적용에 따른 구조 안전성 향상 효과를 확인하였다.

• 설비공학논문집
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• 제11권1호
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• pp.61-72
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• 1999

The present study experimentally investigated the effect of refrigeration lubricant on the heat transfer performance in the straight sections and U-bend of a microfin tube evaporator by using R-22/mineral oil and R-407C/POE oil. The apparatus consisted of test section with U-bend, preheater, condenser, oil injection and sampling devices, magnetic pump, mass flow meter etc. The experimental parameters were oil concentration of 0 to 5 wt%, inlet quality of 0.1 to 0.5, mass flux of 219 and $400kg/m^2s$ and heat flux of 10 and $20kW/m^2$. The effects of parameters on the heat transfer coefficients were large in the order of inlet quality, mass flux and heat flux as oil concentration got increased. As oil concentration was increased, heat transfer coefficients were continuously decreased for R-22 and increased by 3% up to the concentration of 1% and then decreased for R-407C under the condition of large inlet quality, and small mass flux and heat flux. But, the heat transfer coefficients were increased up to the concentration of 3% and then decreased for both R-22 and R-407C refrigerants under the opposite conditions. The variation of enhancement factors for R-407C was under 50% of that for R-22 and the variation with respect to the positions in the test section was small. The pressure drops were increased for both R-22 and R-407C refrigerants as oil concentration was increased. The pressure drops for R-407C were smaller by the maximum of 18% than those for R-22.