• 한국전기전자재료학회논문지
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• 제11권10호
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• pp.861-865
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• 1998

A plate-type linear ultrasonic motor using logitudinal and bending multi-vibration mode was designed and fabricated for the application to card-forwarding device. The stator consisted of PZ-PT-PMS piezoelectric ceramic plate and stainless steel. The performances of the motor were measured. As the experimental results, no-load speed of the motor was 0.6m/s when applied voltage was $80\textrm{V}_{rms}$ in resonance frequency. Starting torque was 1.4 mNm and maximum efficiency was 1.2%.

• 대한기계학회논문집A
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• 제40권1호
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• pp.53-63
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• 2016

자동차 주행 중 도로면으로부터 차량 바퀴에 전달되는 동하중을 측정하기 위해 휠 동력계가 사용된다. 본 논문에서는 전단 변형과 굽힘 변형을 이용한 두 가지 타입의 6축 휠 동력계를 설계하고 비교 평가하였다. 유한요소해석을 이용하여 휠 동력계 기본 구조에 대한 전단 변형 거동과 굽힘 변형 거동을 분석하였으며 이로부터 전단형 휠 동력계와 굽힘형 휠 동력계를 설계하였다. 변형률 해석을 반복 수행하여 각 하중에 대한 출력변형률이 미리 결정된 비슷한 값이 되도록 하고 상호간섭 변형률이 최소화 되도록 설계를 수정하고 브리지 회로를 구성하였다. 전단형 휠 동력계는 균일한 변형률 분포를 얻을 수 있어 제작시 안정된 특성치를 얻을 수 있는 반면에, 굽힘형 휠 동력계는 각 하중에 대한 출력 변형률 값이 더 일정하여 균일한 감도의 좋은 성능을 얻을 수 있을 것으로 예측된다.

• Structural Engineering and Mechanics
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• 제82권5호
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• pp.595-609
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• 2022

Prestressed composite steel-concrete beams are still a technology restricted to repair sites of large-scale structures and spans. One of the reasons for that is the absence of standard frameworks and publications regarding their design and implementation. In addition, the primary normative codes do not address this subject directly, which might be related to a scarcity of papers indicating methods of design that would align the two technics, composite beams and external prestressing. In this context, this paper proposes methods to analyze the sizing of prestressed composite beams submitted to pre-tension and post-tension with a straight or polynomial layout cable. This inquiry inspected a hundred and twenty models of prestressed composite beams according to its prestressing technology and the eccentricity and value of the prestressing force. The evaluation also included the ratio between span and height of the steel profile, thickness and typology of the concrete slab, and layout of the prestressing cables. As for the results, it was observed that the eccentricity of the prestressing force doesn't significantly influence the bending resistance. In prestressed composite beams subjected to a sagging moment, the ratio L/d can reach 35 and 30 for steel-concrete composite slabs and solid concrete slabs, respectively. Considering the negative bending moment resistance, the value of the L/d ratio must be less than or equal to 25, regardless of the type of slab. When it comes to the value of the prestressing force, a variation greater than 10% causes a 2.6% increase in the positive bending moment resistance and a 4% decrease in the negative bending moment resistance. The pre-tensioned composite beams showed a superior response to flexural-compression and excessive compression limit states than the post-tensioned ones.

• Structural Engineering and Mechanics
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• 제6권7호
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• pp.727-746
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• 1998

Finite element models and numerical results are presented for bending and natural vibration using the unified third-order plate theory developed in Part 1 of this paper. The unified third-order theory contains the classical, first-order, and other third-order plate theories as special cases. Analytical solutions are developed using the Navier and L$\acute{e}$vy solution procedures (see Part 1 of the paper). Displacement finite element models of the unified third-order theory are developed herein. The finite element models are based on $C^0$ interpolation of the inplane displacements and rotation functions and $C^1$ interpolation of the transverse deflection. Numerical results of bending and natural vibration are presented to evaluate the accuracy of various plate theories.

• 전자공학회논문지D
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• 제34D권1호
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• pp.41-48
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• 1997

Design rules of directional coupler optical switches are discussed in consideration of parasitic couplings in the bending section. The parasitic coupling phenomenon is analyzed based on the coupled-mode theory and the solutions are represented in the form of the transfer matrix. The modified switching conditions due to the parasitic coupling are derived and the resultant switching diagrams are illustrated. It is revealed that the parallel section's length needs to be adjustd less than the coupling length $l_c(=\pi/2\textsc{k}o)$ to obtain the desired crosstalk and that the adjustment depends on the strength of the parasitic coupling. However, it is discovered that, for weak parasitic coupling, the switching voltage does not need to be altered but may maintain the same value as if no parasitic coupling is taken into account.

• Smart Structures and Systems
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• 제21권1호
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• pp.99-111
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• 2018

Wind induced large bending oscillation amplitudes in tall and slender telecommunication steel towers may lead to precocious fatigue cracks and consequent risk of collapse of these structures, many of them installed in rural areas alongside highways and in highly populated urban areas. Varying stress amplitudes at hot spots may be attenuated by means of passive control mechanical devices installed in the tower. This paper gives an account of both mathematical-numerical model and the technique applied to design and evaluate the performance of a double controller installed in existing towers which is composed by a nonlinear pendulum and a novel type of passive controller described herein as a planar motion disk mounted on shear springs. Results of experimental measurements carried out on two slender tubular steel towers under wind action demonstrate the efficiency of the double controllers in attenuating the towers bending oscillation amplitudes and consequent stress amplitudes extending the towers fatigue life.

• Coupled systems mechanics
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• 제4권1호
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• pp.99-114
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• 2015

In this paper, a refined exponential shear deformation beam theory is developed for bending analysis of functionally graded beams. The theory account for parabolic variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Contrary to the others refined theories elaborated, where the stretching effect is neglected, in the current investigation this so-called "stretching effect" is taken into consideration. The material properties of the functionally graded beam are assumed to vary according to power law distribution of the volume fraction of the constituents. Based on the present shear deformation beam theory, the equations of motion are derived from Hamilton's principle. Analytical solutions for static are obtained. Numerical examples are presented to verify the accuracy of the present theory.

• 한국안전학회지
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• 제25권3호
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• pp.34-39
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• 2010

Unidirectional Carbon Fiber Reinforced Plastics (CFRP) are advanced materials which combine the characteristics of the light weight, high stiffness and strength. For those reasons, the use of the unidirectional CFRP has increased in jet fighters, aerospace structures. However, unidirectional CFRP composites have a lot of problems, especially delamination, compared with traditional materials such as steels and aluminums, and so forth. Therefore, the interlaminar fracture toughness for a laminate CFRP composite is very important. In this study, The mode II interlaminar fracture toughness was measured by using center notched flexure(CNF) test specimen. The CNF specimens using unidirectional carbon prepreg were fabricated by a hot-press with the gage pressure and temperature controller. And three kinds of a/L ratio was applied to these specimens. Here, we discuss the relations of the crack growth and the mode II interlaminar fracture under the four point bending CNF test. From the results, we shows that mode II interlaminar was occurred when the more $a_0$/L ratio, the less load. And $G_{IIC}$ also were obtained as 5.33, 2.9 and $0.58kJ/m^2$ according to $a_0$/L ratio=0.2, 0.3 and 0.4.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권9호
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• pp.427-433
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• 2001

A linear ultrasonic motor was designed by a combination of the first longitudinal and fourth bending mode, and the motor consisted of a straight aluminum alloys bar bonded with a piezoelectric ceramic element as a driving element. That is,$L_1-B_4$ linear ultrasonic motor can be constructed by a multi-mode vibrator of longitudinal and bending modes. Linear ultrasonic motors are based on an elliptical motion on the surface elastic body, such as bar or plates. In general, the natural resonance frequency of the stator is used as a driving frequency of the motor which provides a large elliptical motion. The corresponding eigenmode of one resonance frequency can be excited twice at the same time with a Phase shift of 90 degrees in space and time. And the rotation can be reversed by changing the phase between the two signals from sin$\omega$t to cos$\omega$t. Moreover, the tangential force pushes the slider(rotor) and, therefore, determines the thrust and speed of the motor. The experimental results of fabrication motors, bimorph-tyPe motor showed more excellent than unimorph-type. The maximum speed of TBL-200, TBL-300, TBL-400, TBL -220, TBL-310 and TBL-420 motors were 0.12, 0.37, 0.39, 0.14, 0.55 and $0.60ms6{-1}$, respectively. And the efficiency were reported 1.15, 7.9, 6.6, 2.36, 10.1 and 16.5%, respectively. That time, output thrust of the motor was a strong(1~2N) and the weight of stator was a lightness(5~7g).

• 한국공작기계학회논문집
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• 제16권3호
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• pp.109-116
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• 2007

The present study examined mechanical properties according to the change of outer circumference in the friction welding of A2024-T4 stock, which is used much as aircraft structure, truck wheel, stainless materials and A2024-T4 stock with 10 hollow at the center. Welding conditions were fixed at RPM 2,000rpm, friction pressure of 50MPa, friction time of 1.5sec, upset pressure of 120MPa and upset time of 2.0 seconds. From the result of this study were drawn conclusions as follows : According to the result of a tensile strength test, the solid shaft showed linear increase of tensile strength with the change of outer circumference, the hollow shaft showed maximum tensile stength when the length (L) was 2mm and decrease of tensile strength with the change of outer circumference, hardness appeared to increase and then decrease for welding interface, and it showed maximum hardness 155Hv at L=5mm of the solid shaft. Bending strength increased linearly far change of the distance (L) of outer circumference in the solid shaft and then decreased linearly in the hollow shaft. the result of examining tissue, the tissue grew finer around the welding interface and divided the basic material and the welding surface.