• Journal of the Microelectronics and Packaging Society
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• v.27 no.2
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• pp.19-26
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• 2020

Flexible displays have been evolved into curved, foldable, and rollable as the degree of bending increases. Due to the presence of brittle electrodes (e.g. indium-tin oxide (ITO)) that easily cracked and delaminated under severe bending deformation, lowering mechanical stress of the electrodes has been critical issue. Because of this, mechanical stress of brittle electrode in flexible displays has been analyzed mostly in terms of bending radius. On the other hand, in order to make rollable display, various mechanical components such as roller and spring are needed to roll-up or extend the screen for the rollable display apparatus. By these mechanical components, brittle electrode in the rollable display is subjected to the excessive tensile stress due to the retracting force as well as the bending stress by the roller. In this study, mechanical deformation of rollable OLED display was modeled considering boundary conditions of the apparatus. An analytical modeling based on the classical beam theory was introduced in order to investigate the mechanical behavior of the rollable display. In addition, finite element analysis (FEA) was used to analyze the effect of mechanical components in the apparatus on the brittle electrode. Furthermore, a strategy for improving the mechanical reliability of the rollable display was suggested through controlling the stiffness of adhesives in the display panel.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.1
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• pp.39-46
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• 2013

Smart material such as SMA (Shape Memory Alloy) has been studied in various ways because it can perform continuous, flexible, and complex actuation in simple structure. Smart soft composite (SSC) was developed to achieve large deformation of smart material. In this paper, a shell actuator using woven type SSC was developed to enhance stiffness of the structure while keeping its deformation capacity. The fabricated actuator consisted of a flexible polymer and woven structure which contains SMA wires and glass fibers. The actuator showed various actuation motions by controlling a pattern of applied electricity because the SMA wires are embedded in the structure as fibers. To verify the actuation ability, we measured its maximum end-edge bending angle, twisting angle, and actuating force, which were $103^{\circ}$, $10^{\circ}$, and 0.15 N, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1146-1151
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• 2008

In this paper, the effects of torsional flexibility on a flapping airfoil are investigated. The aerodynamic forces of a torsional flexible flapping airfoil is computed using 2-D unsteady vortex panel method. A typical-section aeroelastic model is used for the aeroelsatic calculation of the flapping airfoil. Torsional flexibility and excitation frequency are considered as main effective parameters. Under heavy airfoil condition , the thrust peak is observed at the points where the frequency ratio is about 0.75. Based on this peak criterion, there exists two different motions. One is an inertia driven deformation motion and the other is an oscillation driven deformation motion. Also, in the thrust peak condition, the phase angle is kept 85 degrees, independent of the torsional flexibility and the excitation frequency.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.3
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• pp.77-81
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• 2020

Commercialization of flexible OLED displays, such as rollable and foldable displays, has attracted tremendous interest in next-generation display markets. However, during bending deformation, cracking and delamination of thin films in the flexible display panels are the critical bottleneck for the commercialization. Therefore, measuring mechanical properties of the fragile thin films in the flexible display panels is essential to prevent mechanical failures of the devices. In this study, tensile properties of the metal and ceramic nano-thin films were quantitatively measured by using a direct tensile testing method on the water surface. Elastic modulus, tensile strength, and elongation of the sputtered Mo, MoTi thin films, and PECVD deposited SiN_x thin films were successfully measured. As a result, the tensile properties were varied depending on the deposition conditions and the film thickness. The measured tensile property values can be applied to stress analysis modeling for mechanically robust flexible displays.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.11a
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• pp.99-106
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• 2001

The design for cold extrusion dies is very important, because the die insert is subjected to very high radial and hoop stresses. The design of cold extrusion dies has many constrained conditions. In this paper, the used assumptions are such that the yield strength of each ring is selected according to the allowable tensile or compressive hoop stress in each ring and the maximum allowable inner pressure, when yielding occurs in one ring of the dies, is obtained by the proposed equation. In order to obtain design variables, such as diameter ratios and interferences, using the maximum inner pressure, the flexible tolerance method was used for shrink-fitted thick-walled cylinders. ANSYS APDL was used to perform the repeated analysis of deformation of the dies due to the variation of the design variables. The response surface methodology is utilized to analyze the relationship between the design variables and the maximum radial displacement of the die insert during extrusion. From the results, it is found that outer diameter of the die Insert has the largest effect on the minimization of maximum radial displacement at the inner surface of the dies.

• Geomechanics and Engineering
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• v.15 no.2
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• pp.755-767
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• 2018

This paper uses a finite element based approach to provide a comprehensive understanding to the behaviour and the design performance of buried uPVC pipes with different diameters. It also investigates pipes with good and poor haunch support and proposes minimum safe wall thicknesses for these pipes. The results for pipes with good haunch support showed that the maximum pipe wall stress and deformation increase as the diameter increased. The results for pipes with poor haunch support showed an increase in the dependency of the developed vertical displacement on the haunch support as the diameter or the backfill height increased. Additionally, poor haunch support was found to increase the soil pressure, with the effect increasing as the diameter increased. The design of uPVC pipes for both poor and good haunch support was found to be governed by critical buckling. A key outcome is a new design chart for the minimum wall thickness, which enables the robust and economic design of buried uPVC pipes. Importantly, the methodology adopted in this study can also be applied to the design of flexible pipes manufactured from other materials, buried under different conditions and subjected to different loading arrangements.

• Journal of the Korean GEO-environmental Society
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• v.7 no.5
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• pp.57-66
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• 2006

In this study, the centrifuge model tests were carried out to evaluate the stress concentration ratio, the deformation modes of piles and the ground movement in clay deposit improved by SCP and GCP piles with changing the replacement ratio(20%, 40%, 60%) under flexible loading. Based on the results obtained, it was shown that the stresses acting on GCP was larger than those acting on SCP with the same replacement ratio. It was evaluated that the average stress concentration ratio of soft clay ground improved by GCP was slightly larger than that of SCP when the replacement ratio is 40%. Only expansion failure occurred in GCP, whereas SCP showed the expansion and shear failure simultaneously.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.285-288
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• 2007

박막형 태양전지 및 플렉서블 태양전지 기판으로 사용되는 금속기판의 우수성은 잘 알려져 있다. 그러나 상용 금속기판이 직면하고 있는 문제점을 보완하기 위해서 전주법으로 제조된 2원합금 금속포일을 개발하였으며, 박막형 및 플렉서블 태양전지의 기판재로 적용가능성을 확인하였다. 일반적으로 태양전지를 제조할 때 열 공정이 수행되며, 이때 기판재와 cell을 구성하는 반도체의 열팽창 계수 차이에 의한 열변형으로 결함이 발생될 수 있고, 태양전지 효율 및 수명을 저하시키는 원인이 될 수 있다. 이러한 원인이 될 수 있는 구성 재료간의 열팽창계수 차이에 의한 cell 의 변형량을 추정하기 위해 유한요소해석 방법을 사용하였다. 유한요소해석을 수행하기 위해 ALGOR 라는 해석 tool 을 사용하였다. 유한요소해석 수행에 사용된 상용 금속인 Mo, Ti, Al, SUS 포일과 전주법으로 제조된 2원합금 금속포일의 열팽창 계수는 실험을 통한 측정치이며, cell을 구성하는 반도체의 열팽창 계수와 열특성은 참고 문헌에 있는 자료들이다. 이 값들을 기반으로 cell 의 구성을 단순화시킨 가상의 태양전지가 제조 공정 온도에서 상온으로 냉각될 때의 열변형량을 계산하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.318-322
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• 1996

This paper presents a technique to control a robot which has a flexible manipulator moving in a vertical plane. The flexible manipulator is modeled as an Euler-Bernoulli beam. Elastic deformation is represented using the assumed modes method. A comparison function which satisfies all geometric and natural boundary conditions of a cantilever beam with an end mass is used as an assumed mode shape. Lagrange's equation is utilized for the development of a discretized model. A control algorithm is developed using a simple PID control technique. The proportional, integral and derivative control gains are determined based on the dominant pole placement method and tuned to show no overshoot and having a short settling time. The effectiveness of the developed control scheme is showed experimentally. In the position control experiment, three different end masses are used. The experimental results shows little overshoot, no steady state error, and less than 2.5 second settling time in case of having an end mass which is equivalent to 45% of the total system weight. Also the residual vibration of the end point is effectively controlled.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.22-32
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• 2001

The numerical investigation of obliquely incident wave interactions with fully submerged dual buoy/porous-membrane floating breakwaters placed in parallel with spacing is studied based on linear potential theory and Darcy's law. The numerical solutions are obtained by using a discrete-membrane dynamic model and second-kind modified Bessel function distribution over the entire boundaries of fluid regions. First, numerical solutions for an idealized dual submerged system without buoys are obtained. Second, a more practical dual submerged system with membrane tension provided by buoys at its tops is investigated by the multi-domain boundary element method particularly devised for dual buoy/porous-membrane problems with gaps. The velocity potentials of wave motion are coupled with porous-membrane deformation, and solved simultaneously since the boundary condition on porous-membrane is not known in advance. The effects of varying permeability on membranes and wave characteristics are discussed for the optimum design parameters of systems previously studied. The inclusion of permeability on membrane eliminates the resonances that aggravate the breakwater performance. The system is highly efficient when waves generated by the buoys and membranes were mutually canceled and its energy at resonance frequency dissipates through fine pores on membranes.