• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.762-769
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• 2017

The extensional stiffness in quasi-isotropic laminates is uniform in the radial direction, but the bending stiffness varies radially due to the stacking sequence. This paper addresses the directional dependency of the bending stiffness and its radial variation in three types of quasi-isotropic laminate reflectors consisting of unidirectional fiber composite materials (UDM) and randomly distributed composite materials (short fiber, RDM). The extensional stiffness and bending stiffness in optical reflectors using RDM are uniform, while the bending stiffness in those using UDM varies radially from 11% to 26%. Also, the stiffness sensitivity, such as the bend-twist or bend-torsion effect, due to the differences in the stiffness value in the composite, is large. These factors are problematic in the optical field requiring precision surfaces. Utilizing RDM might be one way to eliminate the presence of bending stiffness in composite mirror substrates.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.3
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• pp.282-288
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• 1982

크랙탄성평판의 굽힘문제가 경계적분방정식으로 구성되었다. 자연변수인 변위, 수직기울기, 굽힘 모우멘트, 등가전단적과 크랙끝에서 응력의 성장율로 정의되는 응력확대계수들이 주변수로 포함 된다. 이 적분방정식들은 가역에너지 적분이론(Green-Rayleigh)을 기초로 크랙응력분포특성에 맞 게 발전되었으며 해당되는 핵함수들이 유도되었다. 등분석 모우멘트를 받는 중앙크랙이 있는 정 4각형 모형에 대한 응력확대계수가 계산되어 기존의 유한요소법의 해와 비교되었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.938-941
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• 2011

This paper deals with the equivalent shear modulus of the egg-box core. There are three approaches to obtain the equivalent shear modulus of core: a finite element analysis, an analytical study, and an empirical method. In this study, an 3-point bending test is used to evaluate the equivalent shear modulus of the Egg-Box core. As a result of the present work, the equivalent shear modulus of egg-box core at room temperature can be obtained. And this result is compared with the result of finite element analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.259-261
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• 2012

The effect of high-temperature on the flexural modulus of epoxy resin were evaluated using universal testing machine with 3-point bending and dynamic mechanical analyzer. Temperatures of $30^{\circ}C$, $100^{\circ}C$, and $140^{\circ}C$ were considered for flexural test. The specimens having aspect ratio of 16, 32, and 40 were used. The results of storage modulus from DMA were similar to those from flexural test along with given temperatures. It is found that the flexural modulus increased with increasing aspect ratio and the specimen having aspect ratio of above 32 would be suitable for the evaluation of composite material properties under high temperature condition.

• Journal of Power System Engineering
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• v.16 no.6
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• pp.38-44
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• 2012

In this paper, the bending characteristics of the corrugated plates is analyzed. The trapezoidally, triangularlly and sinusoidally corrugated plates are considered. The corrugated plate is treated as an orthotropic plate that has different flexural properties in two perpendicular directions. The equivalent bending and twisting rigidities for the equivalent orthotropic plates are derived. The equivalent flexural rigidities are estimated under the following postulations: (1) The angle of continuously corrugated plate is not changed after the deformation. (2) When the pure bending moment is applied in corrugated direction of the plate, the its plane is in pure bending. Several numerical examples are analyzed with the proposed method and compared with published results.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.55-62
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• 2019

Stiffness-gradient stretchable electronic packages of the soft PDMS/hard PDMS/FPCB structure were processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff flexible printed circuit board (FPCB) as the island substrate. The elastic characteristics of the stretchable packages were estimated and their long-term reliabilities on stretching cycles and bending cycles were characterized. With 0.28 MPa, 1.74 MPa, and 1.85 GPa as the elastic moduli of the soft PDMS, hard PDMS, and FPCB, respectively, the effective elastic modulus of the soft PDMS/hard PDMS/FPCB package was estimated as 0.6 MPa. The resistance of the stretchable packages varied for 2.8~4.3% with stretching cycles ranging at 0~0.3 strain up to 15,000 cycles and for 0.9~1.5% with 15,000 bending cycles at a bending radius of 25 mm.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.207-215
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• 2014

In this paper the radial stiffness associated with stacking sequence effects, and the dimensional stability issue associated with thermally induced surface deformation in quasi-isotropic laminates due to the effect of stacking sequence and additional resin layer technique, are numerically investigated. Finally, the influence of surface resin layer techniques for fiber print-through mitigation in a composite mirror is tested for evaluation of surface accuracy across varying thermal conditions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.10
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• pp.928-934
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• 2013

In this paper, the vibration characteristics of the trapezoidally corrugated plate are investigated by the analytical method. The corrugated plate is widely used as the structural elements because of its high stiffness and light weight. Because the corrugated plate is flexible in the corrugation direction and stiff in the transverse direction, it is treated as an equivalent orthotropic plate to analyze the corrugated plate simply. This equivalent plate must include both extensional and flexural effect to obtain the precise solution. The effective extensional and flexural stiffness of the equivalent plate are derived to consider these effects in the analysis. To demonstrate the validity of the proposed approach, the comparison is made with the previously published results and ANSYS solutions. Some numerical results are presented to check the effect of the geometric properties.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.277-282
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• 2018

In this study, the accuracy and efficiency of a composite rotor blade cross-section analysis program, Ksec2d-AE, which is available at an educational web-based platform called EDISON-CSD, are assessed for possible use in undergraduate structural analysis projects. To this purpose, the convergence of cross-sectional constants by varying the number of finite elements in the cross-section of a wind turbine blade is investigated. The stiffness constants along with the cross-sectional engineering offsets obtained using Ksec2d-AE are validated against a 3D finite element analysis program MSC NASTRAN.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.137-142
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• 2017

Recently, the reduction of vehicle weight has been increasingly studied, in order to enhance the fuel efficiency of passenger cars. In particular, the seat frame is being studied actively, owing to considerations of driver safety from external impact damage. Therefore, this study focuses on high strength steel sheet (SPFC980)/polymer heterojunction hybrid materials, and their performance in regards to impact energy absorption. The ratio of impact energy absorption was observed to be relatively higher in the SPFC980/polymer hybrid materials under the impact load. This was found by calculating the equivalent flexural rigidity, which is the bending effect, according to the Castigliano theorem. An efficient wire-web structure was investigated through the simulation of different wire-web designs such as triangular, rectangular, octagonal, and hexagonal structures. The hexagonal wire-web structure was shown to have the least impact damage, according to the simulations. This study can be utilized for seat frame design for passengers' safety, owing to efficient impact absorption.