• 한국표면공학회지
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• 제48권2호
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• pp.33-37
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• 2015

High efficiency LED device is being concerned due to its high heat loss, and such heat loss will cause a shorter lifespan and lower efficiency. Since there is a demand for the materials that can release heat quickly into the external air, the organic insulating layer was required to be replaced with high thermal conductive materials such as metal or ceramics. Through anodizing the upper layer of Al, the Breakdown Voltage of 3kV was obtained by using an uniform thickness of $60{\mu}M$ aluminum oxide($Al_2O_3$) and was carried out to determine the optimum process conditions when thermal cracking does not occur. Two Ni layers were formed above the layer of $Al_2O_3$ by sputtering deposition and electroplating process, and saccharin was added for the purpose of minimizing the remain stress in electroplating process. The results presented that the 3-layer film including the Ni layer has an adhesive force of 10N and the thermal conductivity for heat dissipation is achieved by 150W/mK level, and leads to improvement about 7 times or above in thermal conductivity, as opposed to the organic insulation layer.

• Coupled systems mechanics
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• 제9권3호
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• pp.237-264
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• 2020

This article investigates the static behaviour of functionally graded (FG) plates sometimes declared as advanced composite plates by using a simple and accurate quasi-3D and 2D hyperbolic higher-order shear deformation theories. The properties of functionally graded materials (FGMs) are assumed to vary continuously through the thickness direction according to exponential law distribution (E-FGM). The kinematics of the present theories is modeled with an undetermined integral component and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate; therefore, it does not require the shear correction factor. The fundamental governing differential equations and boundary conditions of exponentially graded plates are derived by employing the static version of principle of virtual work. Analytical solutions for bending of EG plates subjected to sinusoidal distributed load are obtained for simply supported boundary conditions using Navier'is solution procedure developed in the double Fourier trigonometric series. The results for the displacements and stresses of geometrically different EG plates are presented and compared with 3D exact solution and with other quasi-3D and 2D higher-order shear deformation theories to verify the accuracy of the present theory.

• 한국융합학회논문지
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• 제10권11호
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• pp.297-302
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• 2019

A필러는 주행 중 차량 전복시로 인하여 발생할 수 있는 충격을 완화시켜 탑승자의 신체 보호를 목적으로 안전성에 밀접한 관계가 있다. 그러므로 A필러는 다양한 동적 하중으로부터 이들 부품을 보호해야 한다. 이 제품을 만들기 전에 두 종류의 부품들을 설계하고 차량경량화를 위하여 두께가 조절된 제품을 분석함으로서 본 연구결과는 A필러의 강도 및 내구성에 기여할 수 있다고 사료된다. 본 연구결과를 자동차의 A 필러의 부품에 실제적으로 응용한다면 설계의 내구성 검증에 의하여 그 파손을 방지할 수 있다고 사료된다. 본 연구에서의 자동차의 A필러의 강도 및 내구성 해석에 관한 해석 및 설계 데이터를 이용함으로서 실제적인 자동차에서의 부품에 융합하여 그 미적 감각을 줄 수 있다.

• 마이크로전자및패키징학회지
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• 제19권3호
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• pp.49-56
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• 2012

최근 전자 제품의 소형화, 박형화 및 집적화에 따라 칩과 기판을 연결하는 범프의 미세화가 요구되고 있다. 그러나 범프의 미세화는 직경 감소와 UBM의 단면적 감소로 인하여 전류 밀도를 증가시켜 전기적 단락을 야기할 수 있다. 특히 범프에서 형성되는 금속간화합물과 KV의 형성은 전기적 및 기계적 특성에 큰 영향을 줄 수 있다. 따라서 본 논문에서는 유한요소해석을 이용하여 플립칩 범프의 열변형을 분석하였다. 우선 TCT의 온도조건을 통하여 플립칩 패키지의 열변형 특성을 분석한 결과, 범프의 열 변형이 시스템의 구동에 큰 영향을 미칠 수 있음을 확인하였다. 그리고 범프의 열변형 특성에 큰 영향을 미칠 것을 생각되는 IMC층의 두께와 범프의 직경을 변수로 선정하여 온도변화, 열응력 및 열변형에 대한 해석을 수행하였으며, 이를 통하여 IMC층이 범프에 영향을 미치는 원인에 대한 분석을 수행하였다.

• 한국산학기술학회논문지
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• 제13권7호
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• pp.3207-3215
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• 2012

본 논문에서는 3차 전단변형이론이 고려된 비국소 탄성 이론을 이용한 나노 판의 휨 및 진동에 대하여 연구하였다. 비국소 탄성 이론은 미소 규모 효과를 고려할 수 있고 3차원 전단변형이론은 나노 판의 두께방향으로의 전단 변형률과 전단응력의 곡선변화 효과를 고려할 수 있다. 이러한 두 가지 이론을 이용하여 나노 판의 처짐과 고유진동수에 미치는 비국소 이론의 효과를 제시하였다. 국소 탄성이론과의 관계를 수치해석 결과를 통하여 고찰하였다. 또한 (i) 비국소 계수, (ii) 나노 판의 적층형태, (iii) 나노 판의 보강 방향 그리고 (iv) 나노 판의 적층 수 등이 나노 판의 무차원 처짐에 미치는 효과에 대하여 관찰하였다. 본 연구의 결과를 검증하기 위해 참고문헌의 결과들과 비교 분석하였으며 해석결과는 참고문헌의 결과들과 잘 일치함을 알 수 있었다. 비국소 이론에 의한 나노 판의 처짐에 관한 연구는 향후 관련연구에 비교자료로 활용될 수 있을 것이다.

• 한국항해항만학회지
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• 제26권3호
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• pp.317-322
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• 2002

본 논문은 마그네트 천장크레인 거더에 대한 경량화를 위한 구조최적설계를 수행하였다. 최적화는 ANSYS 소프트웨어를 사용하여 거더의 중량에 대하여 수행되어졌으며, 특히 거더의 상판, 하판, 옆판 그리고 보강판의 두께인 치수에 초점을 맞추었다. 마그네트 크레인의 중량은 처짐, 응력, 고유진동수와 좌굴강도의 제한을 만족하며 약 15%까지 감량되었으며 또한, 구조적인 안전성이 거더의 판넬구조물의 좌굴해석에 의해 입증되었다. 구조최적화로 중량감소에 대해 예로부터 경험적으로 설계된 구조물을 설계하는 것에 매우 유용할 것으로 생각된다. 또한, 본 논문에서는 설계변수들이 목적함수와 상태변수에 미치는 민감도를 평가하였다.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1236-1249
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• 2021

Although there are still controversial opinions and uncertainty on application of SiC_f/SiC composite cladding as next-generation cladding material for its great oxidation resistance in high temperature steam environment and other outstanding advantages, it cannot deny that SiC_f/SiC cladding is a potential accident tolerant fuel (ATF) cladding with high research priority and still in the engineering design stage for now. However, considering its disadvantages, such as low irradiated thermal conductivity, ductility that barely not exist, further evaluations of its in-pile behaviors are still necessary. Based on the self-developed code we recently updated, relevant thermohydraulic and mechanical models in FROBA-ATF were applied to simulate the cladding behaviors under normal and accident conditions in this paper. Even through steady-state performance analysis revealed that this kind of cladding material could greatly reduce the oxidation thickness, the thermal performance of UO₂-SiC was poor due to its low inpile thermal conductivity and creep rate. Besides, the risk of failure exists when reactor power decreased. With geometry optimization and dopant addition in pellets, the steady-state performance of UO₂-SiC was enhanced and the failure risk was reduced. The thermal and mechanical performance of the improved UO₂-SiC was further evaluated under Loss of coolant accident (LOCA) and Reactivity Initiated Accident (RIA) conditions. Transient results showed that the optimized ATF had better thermal performance, lower cladding hoop stress, and could provide more coping time under accident conditions.

• Structural Engineering and Mechanics
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• 제91권1호
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• pp.1-23
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• 2024

This paper formulates a new integral shear deformation shell theory to investigate the free vibration response of carbon nanotube (CNT) reinforced structures with only four independent variables, unlike existing shell theories, which invariably and implicitly induce a host of unknowns. This approach guarantees traction-free boundary conditions without shear correction factors, using a non-polynomial hyperbolic warping function for transverse shear deformation and stress. By introducing undetermined integral terms, it will be possible to derive the motion equations with a low order of differentiation, which can facilitate a closed-form solution in conjunction with Navier's procedure. The mechanical properties of the CNT reinforcements are modeled to vary smoothly and gradually through the thickness coordinate, exhibiting different distribution patterns. A comparison study is performed to prove the efficacy of the formulated shell theory via obtained results from existing literature. Further numerical investigations are current and comprehensive in detailing the effects of CNT distribution patterns, volume fractions, and geometrical configurations on the fundamental frequencies of CNT-reinforced nanocomposite shells present here. The current shell theory is assumed to serve as a potent conceptual framework for designing reinforced structures and assessing their mechanical behavior.

• 한국강구조학회 논문집
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• 제14권4호
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• pp.481-487
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• 2002

콘크리트충전 강관기둥의 외다이아프램 접합부형식에서, 철골보의 하중이 내부의 콘크리트로 전달되는 하중전달 메카니즘이 아직 명확하게 규명되지 않았다. 여기서 각 층에서 철골보의 전단력은 외부의 강관과 내부의 콘크리트 사이의 부착응력에 의해 전달된다고 본다. 따라서 본 연구는 콘크리트충전 강관기둥의 부착응력을 파악하기 위해, 콘크리트면에만 하중을 가하는 단순가력실험을 실시하였다. 콘크리트 종류, 강관의 형상/길이, 이음부의 유무/뒷댐재의 두께 등을 변수로 총 30개의 실험체를 제작하여 실험을 실시했으며, 각 변수에 따른 실험결과를 비교/분석하고자 했다.

• Restorative Dentistry and Endodontics
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• 제21권1호
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• pp.321-338
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• 1996

The purpose of this study was to evaluate the effect of moistening and air-drying of acid conditioned dentin and enamel on the marginal microleakage. In this study, Class V cavity were prepared on both buccal and lingual surface of sixty extracted human premolars with cementum margin. These specimens were randomly devided into three groups and three dentin adhesives(Scotchbond Multi-Purpose, All bond 2, Prisma Universal Bond 3) were applied to each group. The specimens in each group were subdevided into four groups (Wet/primed, Dry/primed, Wet/not primed, Dry/not primed) and the etched dentin and enamel surface were treated these four surface treatments prior to the placement of a bonding agent or adhesive. Wet/primed group was simply blot-dried with a damp facial tissue before primer placement ; Dry/primed group was air dried for 30 seconds before the placement of a primer ; Wet/not primed group and Dry/not primed group were not primed after blot dried and air dried for 30 seconds each group. The bonding agent and composite resin were applied for each group. All specimens were exposed to 500 cycle of thermal stress. Specimens were placed in a silver nitrate solution and then sectioned buccolingually through the center of the restoration. The dye penetrations of the specimens were observed with a stereo microscope. The statistical test were applied to the results using a one way analysis variance (ANOVA) and Duncan's multiple range test. The aspects of silver ion penetration into the resin/dentin interface were examined under scanning electron microscopy. The results were as follows. 1. In all groups, the enamel margin showed significantly lower leakage value than the cementum margin (p<0.05). 2. Regardless of various surface treatment and dentin adhesives, there was no significant difference at the enamel margins (p>0.05). 3. At the dentin margins, the leakage values of Dry/not primed group showed significantly higher than that of the other groups (p<0.05). The leakage values of Wet/primed group showed significantly lower than that of the other groups, but, there was no significant difference between Wet group and Dry group. 4. There was no significantly difference between the dentin adhesives regarding the surface treatments in all groups(p>0.05). 5. On the backscatterd scanning electron microscopy observation, the penetration of the silver ion occured at the bonding resin/dentin interface. In the Wet/primed group, resindentin hybrid zone and resin penetration into the dentin was observed. The resin tags were compactively formed to a thickness of $3\sim4{\mu}m$ at the upper part of dentinal tubules. In the Dry/primed group, the thickness of the hybrid zone and the diameter, depth of the resin tags diminished. In the Non-primed groups, the hybrid zone was not identified and few resin tag was observed. There was the gap formation in the resin/dentin interface.