• Structural Engineering and Mechanics
• /
• 제36권6호
• /
• pp.679-695
• /
• 2010

In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Bruel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending, extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 A
• /
• pp.147-149
• /
• 1995

The stabilization of the conductor in superconducting power cable is very important from the view point of protection. In this study, critical thicknesses of superconducting layer of $Nb_{3}Sn$ conductor and stabilizer Cu have been estimated under the adiabatic condition. The bending stress of $Nb_{3}Sn$/SUS composite superconducting tape on the curvature radius was also evaluated.

• Advances in materials Research
• /
• 제8권2호
• /
• pp.75-81
• /
• 2019

Through experimental and numerical studies of metal forming processes by plastic deformation, this paper represents a numerical simulation by finite element of the mechanical behavior of the material during a permanent deformation phenomenon. The main interest of this study is to optimize the shaping processes such as folding. In this context the elastic return for the folding process has been further reduced by using the design of experiments approach. In this analysis, it is proposed to consider the following factors: bending radius, metal-sheet thickness, gap and length of the fold.

• Advances in nano research
• /
• 제13권1호
• /
• pp.47-61
• /
• 2022

The present research investigates the dynamic behavior of a rotating functionally graded (FG) nonlocal cylindrical beam. The cylindrical beam is mathematically modeled via third-order beam theory linked with nonlocal strain gradient theory. The tube structure is made of functionally graded materials composed of Aluminum oxide coated on the Nickel, which the mechanical properties vary in the tube radius direction according to the power law. The bending harmonic force is applied in the tube length middle. The nonlocal spinning equations of the tube are derived via the energy method of the Hamilton principle, and they are solved via a robust numerical procedure for different boundary conditions. The main application of the rotating nanostructures is for the production of small-scale motors and devices and the drug-delivery application, the presented results can help the researcher have a better view regarding the different conditions.

• 한국진공학회지
• /
• 제10권4호
• /
• pp.431-439
• /
• 2001

비정질 다이아몬드 박막(amorphous-Diamond a-B)을 증착하기 위하여 제작된 Filtered Vacuum Arc Source (FVAS)는 60도의 굽힘 각도를 가지는 토러스형 구조로 토러스 반경 266 mm, 플라즈마 덕트 반경 80 % 전체 길이 600 mm이며, 1 개의 영구자석 및 5 개의 전자석으로 되어있다. 플라즈마 덕트는 임의의 전압을 인가할 수 있도록 전기적으로 절연 시켰으며, 덕트 내부는 배플을 설치하여 macro-particle의 되튐 현상을 방지하였다. 사용된 음극은 직경 80 mm의 graphite이다. 각 전자석이 플라즈마 인출에 미치는 영향은 taguchi 실험계획법을 이용, 수치 모사와 실험을 행하였다. 소스 전자석과 인출 전자석은 아크의 안정성에 영향을 주었고, 빔 인출 전류는 낮은 소스 전자석 전류와 특정한 필터 전자석 전류에서 최대값을 나타내었다. 이때 소스, 인출, 굽힘, 반사, 출구 전자석의 전류값은 1 A, 3 A, 5 A, 5 A, 5 A였으며, 아크 전류 30 A일 때, 빔 전류 밀도 3.2 mA/$\textrm{cm}^2$, 평균 증착률 5 $\AA$/sec를 얻었다. 또한 플라즈마 덕트의 바이어스 전압 증가에 따라, 빔 전류 밀도는 증가하였으며, 더 효율적인 빔을 인출할 수 있었다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 추계학술대회 논문집
• /
• pp.322-325
• /
• 2005

In order to make a doubly-cowed sheet metal effectively, the sheet metal forming process has been developed by adopting the flexibility of the incremental forming process and the principle of bending deformation which causes slight deformation in thickness. The developed process is an unconstrained forming process without holder. The experimental equipment has been set up with the roll set which consists of two pairs of support rolls and one center roll. In order to analyze process parameters in the incremental roll forming process for the application to doubly curved ship hull plate, the orthogonal array is adopted. From the FEM results, among the process parameters, the distance between supporting rolls in pairs along the direction of one principal radius of curvature as well as the forming depth is shown to influence the generation of curvature in the same direction significantly. That is, the other distance between supporting rolls in pairs which are not located in the same direction of one principal radius of curvature, does not have an significant effect on the generation of the curvature in that direction. Also, the forming load and torque from the FEM simulation are acceptable to the system development of the incremental roll forming process for the forming of ship hull plate.

• 한국자동차공학회논문집
• /
• 제14권1호
• /
• pp.79-85
• /
• 2006

CFRP(Carbon Fiber Reinforced Plastics) of the advanced composite materials as structural materials for vehicle, has a wide application in light-weigh structural materials of airplanes, ships and automobiles because of high strength and stiffness, However, there is a design variable to be considered in practical application of the laminate composite materials, these materials are vulnerable to transverse impact. This paper is to study the effects of stacking sequence and curvature on the penetration characteristics of composite laminate shell. They are stacked to $[0_3/90_3]S,\;[90_3/0_3]s\;and\;[0_2/90_3/0]s,\;[90_2/0_3/90]s$ and their interlaminar number two and four. They are manufactured to various curvature radius (R=100, 150, 200mm and $\infty$), When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determing the time for it to pass two ballistics-screen sensors located a known distance apart. The critical penetration energy of specimen A and B with less interfaces were a little higher than those of C and D. As the curvature increases, the critical penetration energy increases linearly because the resistance to the in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. The specimen A and C have higher critical penetration energy than B and D because of different stacking sequences. We examined crack length through a penetration test. For the specimen A with 2interfaces, the longest circumferential direction crack length were observed on the first interface from the impact point. For the specimen B 4-interface, the longest circumferential direction crack length were observed on the second interface from the impact point.

• 한국구조물진단유지관리공학회 논문집
• /
• 제18권4호
• /
• pp.77-83
• /
• 2014

PSC거더교는 탁월한 안정성, 사용성 등의 특징으로 전세계적으로 가장 많이 사용되는 교량의 한 형식이다. 그러나, 긴장재 (강연선)의 시공오차나 곡률반경 등에 의하여 절곡되는 상황이 발생하는 경우가 생기며, 이는 국부적인 긴장력의 손실울 유발한다. 그러나, 일반적으로 설계와 시공과정에서는 긴장재의 국부적인 절곡으로 발생하는 긴장력의 손실에 대하여는 간과하고 있다. 이 연구에서는 PSC 거더 연속화 지점부에서 시공오차와 선형반경으로 인하여 발생하는 긴장력 손실량을 실험적으로 규명하였다. 또한, 국부적 긴장력 손실을 감소시킬수 있는 공법을 제안하고 이에 대한 효용을 실험으로 검증하였다. 실험결과에 따르면 국부적 절곡에 의해 최대 10%의 긴장손실이 나타났고, 블록아웃 공법을 통해 손실률을 최대 약 5% 감소시킬 수 있는 것으로 나타났으며, 이는 블록아웃 공법으로 연속화 교량의 긴장효율을 향상시킬 수 있음을 의미한다.

• 한국인터넷방송통신학회논문지
• /
• 제16권2호
• /
• pp.165-170
• /
• 2016

곡면형 플라즈마 도파로에 기초한 나노 크기의 전력분배기가 다중모드 간섭 결합기의 특성을 이용하여 설계되었다. 플라즈마 곡면형 다중모드 간섭 결합기(PC-MMIC)의 적응 특성을 쉽게 분석하기 위하여 등각변환 해석법을 이용하여 곡면형 구조를 평면형 구조로 등가 변환하였다. 또한, 3D 전송구조의 전파특성과 최적의 설계변수를 선택하기 위하여 유효 유전체 방법과 종방향 모드 전송 선로 해석법을 적용하였다. 설계된 $2{\times}2$ PC-MMIC는 휘어진 구조에 기인하여 quasi-TM 모드에서는 PC-MMIC의 특성이 나타내지 않았으며, quasi-TE 모드의 경우 50%:50%의 비율로 출력되는 3dB 결합특성이 나타나지 않았다. 더욱이, 곡률 반경이 작은 부분 보다 큰 부분에서 입사된 신호가 더욱 좋은 결합특성을 나타내었다.

• Restorative Dentistry and Endodontics
• /
• 제47권2호
• /
• pp.16.1-16.9
• /
• 2022

Objectives: This study compared the cyclic fatigue resistance of One Curve (C wire) and F6 Skytaper (conventional austenite nickel-titanium [NiTi]), and 2 instruments with thermos-mechanically treated NiTi: Protaper Next X2 (M wire) and Hyflex CM (CM wire). Materials and Methods: Ten new instruments of each group (size: 0.25 mm, 6% taper in the 3 mm tip region) were tested using a rotary bending machine with a 60° curvature angle and a 5 mm curvature radius, at room temperature. The number of cycles until fracture was recorded. The length of the fractured instruments was measured. The fracture surface of each fragment was examined with a scanning electron microscope (SEM). The data were analyzed using one-way analysis of variance and the post hoc Tukey test. The significance level was set at 0.05. Results: At 60°, One Curve, F6 Skytaper and Hyflex CM had significantly longer fatigue lives than Protaper Next X2 (p < 0.05). No statistically significant differences were found in the cyclic fatigue lives of One Curve, F6 Skytaper, and Hyflex CM (p > 0.05). SEM images of the fracture surfaces of the different instruments showed typical features of fatigue failure. Conclusions: Within the conditions of this study, at 60° and with a 5 mm curvature radius, the cyclic fatigue life of One Curve was not significantly different from those of F6 Skytaper and Hyflex CM. The cyclic fatigue lives of these 3 instruments were statistically significantly longer than that of Protaper Next.