• Advances in aircraft and spacecraft science
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• 제9권4호
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• pp.301-318
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• 2022

This paper presents the free vibration analysis of 3D printed sandwich beams by using high-order theories based on the Carrera Unified Formulation (CUF). In particular, the component-wise (CW) approach is adopted to achieve a high fidelity model of the printed part. The present model has been used to build an accurate database for collecting first natural frequency of the beams, then predicting Young's modulus based on an inverse problem formulation. The database is built from a set of randomly generated material properties of various values of modulus of elasticity. The inverse problem then allows finding the elastic modulus of the input parameters starting from the information on the required set of the output achieved experimentally. The natural frequencies evaluated during the experimental test acquired using a Digital Image Correlation method have been compared with the results obtained by the means of CUF-CW model. The results obtained from the free-vibration analysis of the FDM beams, performed by higher-order one-dimensional models contained in CUF, are compared with ABAQUS results both first five natural frequency and degree of freedoms. The results have shown that the proposed 1D approach can provide 3D accuracy, in terms of free vibration analysis of FDM printed sandwich beams with a significant reduction in the computational costs.

• Steel and Composite Structures
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• 제50권1호
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• pp.63-75
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• 2024

In this paper, the modified couple stress theory (MCST) and first order shear deformation theory (FSDT) are employed to investigate the free vibration and bending analyses of a three-layered micro-shell sandwiched by piezoelectric layers subjected to an applied voltage and reinforced graphene nanoplatelets (GPLs) under external and internal pressure. The micro-shell is resting on an elastic foundation modeled as Pasternak model. The mixture's rule and Halpin-Tsai model are utilized to compute the effective mechanical properties. By applying Hamilton's principle, the motion equations and associated boundary conditions are derived. Static/ dynamic results are obtained using Navier's method. The results are validated with the previously published works. The numerical results are presented to study and discuss the influences of various parameters on the natural frequencies and deflection of the micro-shell, such as applied voltage, thickness of the piezoelectric layer to radius, length to radius ratio, volume fraction and various distribution pattern of the GPLs, thickness-to-length scale parameter, and foundation coefficients for the both external and internal pressure. The main novelty of this work is simultaneous effect of graphene nanoplatelets as reinforcement and piezoelectric layers on the bending and vibration characteristics of the sandwich micro shell.

• Structural Engineering and Mechanics
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• 제91권1호
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• pp.87-102
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• 2024

In recent years, the focus on vibration analysis of multilayer smart structures has attracted considerable attention in many engineering applications. In this work, vibration analysis of a three-layer microporous beam with a core amplified by a composite material reinforced with graphene platelets and two piezoelectric thin films is discussed. It is assumed that piezoelectric layers with a thickness of 0.01 core are very thin and the properties of the matrix and reinforcement vary in the thickness directions. The governing equations of motion are obtained using an energy approach and the method of numerical differential quadrature to solve them. The results of this work are compared to other research and there is good agreement between them. The influences of the volumetric weight fraction of graphene wafers, different graphene platelets distributions, porosity distribution, mass scale parameters and thin ratio of graphene platelets take into account the natural dimensionless frequencies of the micro-beam. The results of this study show that the symmetric distribution of graphene platelets based on the symmetric porosity distribution has a great influence on the natural frequencies without basic dimension of the micro-beam, while the shape ratios of graphene platelets do not have a significant influence on natural frequency changes.

• 한국항공우주학회지
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• 제45권1호
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• pp.30-35
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• 2017

본 연구에서는 디지털 영상 상관 기법을 이용하여 알루미늄 하니콤 샌드위치 보의 고유 진동수를 계측하였다. 고속 디지털 카메라를 이용하여 보의 진동 영상을 획득하고 디지털영상 상관 기법을 이용하여 변위를 계산하였다. 시간 영역에서의 변위 데이터를 고속 퓨리에 변환하여 주파수 영역의 응답으로 변환하였다. 랜덤 가진에 따른 주파수 영역에서의 잡음을 줄이기 위하여 스펙트럼 평균화 기법과 Savitsky-Golay 디지털 필터를 사용하였다. 가속도계를 이용한 기존의 방법 및 유한요소 해석 결과와의 비교를 통하여 방법의 정확성을 확인하였다. 결론적으로 고속 디지털 카메라와 디지털 영상 상관 기법을 이용하는 새로운 방법은 구조물의 진동을 잘 측정할 수 있음을 보였고, 센서를 부착하기 어려운 바이오 구조 등의 진동 계측에 적용할 수 있을 것이다.

• 비파괴검사학회지
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• 제37권2호
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• pp.91-98
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• 2017

Recently, composite materials have been mainly used in the main wings, ailerons, and fuselages of aircraft and rotor blades of helicopters. Composite materials used in rapid moving structures are subject to impact by hail, lightning, and bird strike. Such an impact can destroy fiber tissues in the composite materials as well as deform the composite materials, resulting in various problems such as weakened rigidity of the composite structure and penetration of water into tiny cracks. In this study, experiments were conducted using a 2 kW halogen lamp which is most frequently used as a light source, a 2 kW near-infrared lamp, which is used for heating to a high temperature, and a 6 kW xenon flash lamp which emits a large amount of energy for a moment. CFRP composite sandwich panels using Nomex honeycomb core were used as the specimens. Experiments were carried out under impact damages of 1, 4 and 8 J. It was found that the detection of defects was fast when the xenon flash lamp was used. The detection of damaged regions was excellent when the halogen lamp was used. Furthermore, the near-infrared lamp is an effective technology for showing the surface of a test object.

• 한국농공학회논문집
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• 제46권4호
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• pp.39-46
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• 2004

This experiment was carried out to study on the effect of surface coating on thermal insulation of farm structures to improve thermal resistance and reflective effect of solar radiation. Nine different types of experimental specimen were compared in the temperature variations of inside and outside; A, B, C, D. E and F types are box container and G, H and I types are drum container. The size of these containers is $1,500{\times}2,000{\times}2,500$ mm and ${\varphi}$ $280{\times}330$ mm, respectively. Specimen of 3-type box(A, B, C) is galvanized steel sheet of thickness 0.45 mm. D, E and F types are sandwich panel of the thickness 50 mm inserted with urethane, glass wool and polystyrene form, respectively. G, H and I types are paint pot using in general. The surface of A. D, E, F and I types didn't any treatment, B, C and G types were treated with thermal insulation coating on the outside surface(B, G) or the inside and outside surface(C). And H type was treated with water paint coating on the only outside surface. In general, the experimental results showed the following tendencies; In case of A, B and C types. it was found that the thermal insulation effect of types coated with thermal insulation coating was improved remarkably than that of no treatment. And the thermal insulation effect between steel sheet and sandwich panel type was nearly similar There was not a significant difference of thermal insulation effect between thermal insulation coating and water paint coating. In time of drum container filled with rough rice, The difference of heat transfer tendency and temperature variation among surface treatments was nearly similar that of box types of galvanized steel sheet. And there was time lag about 6 hours between the temperature of middle part of rice and that of inside or outside surface.

• Bulletin of the Korean Chemical Society
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• 제34권3호
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• pp.725-730
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• 2013

An investigation of the coordination behavior of sulfur-containing mixed-donor tribenzo-macrocycles $L^1-L^3$ ($L^1$: 20-membered $O_3S_2$, $L^2$: 20-membered $O_2S_3$, and $L^3$: 23-membered $O_4S_2$) with $d^{10}$-metal ($Ag^+$, $Hg^{2+}$, and $Pb^{2+}$) salts is reported. The X-ray structures of five complexes (1-5) with different structural types and stoichiometries, including mono- to dinuclear species have been determined. Reactions of $L^2$ and $L^3$ with the silver(I) salts ($PF_6{^-}$ and $SCN^-$) afforded two dinuclear 2:2 (metal-to-ligand) complexes with different arrangements: a sandwich-type cyclic dinuclear complex $[Ag_2(L^2)_2](PF_6)_2{\cdot}3CH_2Cl_2$ (1) and a linear dinuclear complex $[Ag_2(L^3)_2(SCN)_2]$ (2), in which two monosilver(I) complex units are linked by an Ag-Ag contact. Reactions of $L^1$ and $L^2$ with mercury(II) salts ($SCN^-$ and $Cl^-$) gave a mononuclear 1:1 complexes $[Hg(L^1)(SCN)_2]$ (3) and $[Hg(L^2)Cl_2]$ (4) with anion coordination in both cases. $L^2$ reacts with lead(II) perchlorate to yield a mononuclear sandwich-type complex $[Pb(L^2)_2(ClO_4)_2]$ (5), giving an overall metal coordination geometry of eight with a square antiprism arrangement. From these results, the effects of the donor variation and the anioncoordination ability on the resulting topologies of the soft metal complexes are discussed.

• 한국정밀공학회지
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• 제26권11호
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• pp.116-123
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• 2009

The elastic properties of core affect mechanical properties and deformation behaviours of the lightweight sandwich panel. The objective of the present paper is to estimate experimentally Young's and shear moduli of a core in internally structured boned (ISB) panel with woven metal as inner structures using the deflection theory of sandwich beam considered core stiffness. Three points bending experiments were performed to obtain force-deflection curves of the designed ISB panel in each material direction. The elastic and shear moduli of the core in each material direction were estimated from slopes and intercepts of relationships between compliance per the span length and square of the span length, respectively. The results of the estimation showed that the fabric technology of the woven metal affects the variation of the elastic properties in the core. Through the comparison of shear moduli and force-deflection curves of the proposed method and those without considering the core stiffness, it was shown that the core stiffness should be considered to estimate properly the Young's and shear moduli of ISB panels. Finally, the contribution ratio of bending and shear deflections of ISB panels to the total deflection was quantitatively examined.

• 한국가스학회지
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• 제7권1호
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• pp.28-32
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• 2003

대체 facing material 소재로 유력시되는 FRP를 사용하여 facing material이 갖추어야할 압축, 인장 등 기계적 물성과, vapor barrier도, 화학적 안전성 등을 조사한 결과 모든 면에서 기존의 plywood보다 우수한 성질을 나타냄을 밝혔다. 본 연구의 결과로서 대체 facing material로 FRP를 사용할 경우 LNG 저장 탱크의 안전성이 향상되고 높은 vapor barrier기능으로 인해 탱크의 성능이 향상되는 등 다양한 장점을 나타냄을 알 수 있게 되었다. 따라서 본 연구의 결과는 LNG 저장 탱크의 성능을 개선하는데 기여하며, LNG 저장 탱크용 합판의 대체연구에 적극적으로 활용될 수 있을 것으로 사료된다.

• Composites Research
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• 제22권5호
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• pp.1-7
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• 2009

WR580/NF4000 유리섬유 에폭시 면재를 갖는 알루미늄 하니컴 샌드위치 복합재가 적용된 자동무인경전철 차체 구조물은 구조 시험과 유한요소 해석에 의해 평가되었다. 구조 시험은 JIS E 7105 규정에 따라 수행되었다. 차체 구조물의 추조 안전성은 다이얼 게이지와 가속도 센서를 통해 얻어진 처짐 및 고유진동수 결과에 의해 평가되었다. 그리고 제안된 유한요소 모델은 구조 시험 결과와 비교 되었으며, 유한요소 해석은 구조 시험과 잘 일치함을 보였다. 또한, 차제 구조물의 강성을 높이기 위해 언더프레임에 보강재가 적용된 모델은 설계단계에서 제안되었다. 보강된 언더프레임 모델을 갖는 복합재 차체 구조물은 구조 강성이 약 44%가 향상되었다.