• Structural Engineering and Mechanics
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• 제73권5호
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• pp.555-563
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• 2020

The objective of present paper is assessment of dynamic buckling behavior of an embedded sandwich microplates in thermal environment in which the layers are reinforced through functionally graded carbon nanotubes (FG-CNTs). Therefore, mixture rule is taken into consideration for obtaining effective material characteristics. In order to model this structure much more realistic, Kelvin-Voigt model is presumed and the sandwich structure is rested on visco-Pasternak medium. Exponential shear deformation theory (ESDT) in addition to Eringen's nonlocal theory are utilized to obtain motion equations. Further, differential cubature method (DCM) as well as Bolotin's procedure are used to solve governing equations and achieve dynamic instability region (DIR) related to sandwich structure. Different parameters focusing on volume percent of CNTs, dispersion kinds of CNTs, thermal environment, small scale effect and structural damping and their influences upon the dynamic behavior of sandwich structure are investigated. So as to indicate the accuracy of applied theories as well as methods, the results are collated with another paper. According to results, presence of CNTs and their dispersion kind can alter system's dynamic response as well.

• Structural Engineering and Mechanics
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• 제78권5호
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• pp.557-572
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• 2021

The current study considers free vibration of the spherical panel with magnetorheological (MR) fluids core and magneto-electro-elastic face sheets. The panel is subjected to electro-magnetic loads and also is located on an orthotropic visco-Pasternak elastic foundation. To describe the displacement components of the structure, the first-order shear deformation theory (FSDT) is used and the motion equations are extracted by employing Hamilton's principle. To solve the motion differential equations, Navier's method is selected as an exact analytical solution for simply supported boundary conditions. Effect of the most important parameters such as magnetic field intensity, loss factor, multi-physical loads, types of an elastic medium, geometrical properties of the panel, and also different material types for the face sheets on the results is considered and discussed in details. The outcomes of the present work may be used to design more efficient smart structures such as sensors and actuators.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.745-756
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• 2022

This study aims to determine the cause of the load resistance loss in storage racks that can be attributed to external forces such as earthquakes and to improve safety by developing reinforcement systems that can prevent load resistance loss. To this end, a static cyclic loading test was performed on pallet racks commonly used in logistics warehouses. The test results indicated that a pallet rack exposed to an external force loses more than 50% of its load resistance owing to the damage caused to column-beam joints. Three reinforcement systems were developed for preventing load resistance loss in storage racks exposed to an external force and for performing differentiated target functions: column reinforcement device, seismic damper, and viscoelastic damper. Shake table testing was performed to evaluate the earthquake response and verify the performance of these reinforcement systems. The results confirmed that, the maximum displacement, which causes the loss of load resistance and the permanent deformation of racks under external force, is reduced using the developed reinforcement devices. Thus, the appropriate selection of the developed reinforcement devices by users can help secure the safety of the storage racks.

• Geomechanics and Engineering
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• 제33권3호
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• pp.271-277
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• 2023

This article investigates the effect of viscoelastic foundations on the waves' dispersion in a beam made of ceramic-metal functionally graded material (FGM) with microstructural defects. The beam is considered to be shear deformable, and a simple three-unknown sinusoidal integral higher-order shear deformation beam theory is applied to represent the beam's displacement field. Novel to this study is the investigation of the impact of viscosity damping on imperfect FG beams, utilizing a few-unknowns theory. The stresses and strains are obtained using the two-dimensional elasticity relations of FGM, neglecting the normal strain in the beam's depth direction. The variational operation is employed to define the dispersion relations of the FGM beam. The influences of the material gradation exponent, the beam's thickness, the porosity, and visco-Pasternak foundation parameters are represented. Results showed that phase velocity was inversely proportional to the damping and porosity of the beams. Additionally, the foundation viscous damping had a stronger influence on wave velocity when porosity volume fractions were low.

• Earthquakes and Structures
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• 제24권2호
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• pp.127-140
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• 2023

The vibration of microtubule in human cells is the source of electrical field around it and inside cell structure. The induction of electrical field is a direct result of the existence of dipoles on the surface of the microtubules. Measuring the electrical fields could be performed using nano-scale sensors and the data could be transformed to other computers using internet of things (IoT) technology. Processing these data is feasible by artificial intelligence-based methods. However, the first step in analyzing the vibrational behavior is to study the mechanics of microtubules. In this regard, the vibrational behavior of the microtubules is investigated in the present study. A shell model is utilized to represent the microtubules' structure. The displacement field is assumed to obey first order shear deformation theory and classical theory of elasticity for anisotropic homogenous materials is utilized. The governing equations obtained by Hamilton's principle are further solved using analytical method engaging Navier's solution procedure. The results of the analytical solution are used to train, validate and test of the deep neural network. The results of the present study are validated by comparing to other results in the literature. The results indicate that several geometrical and material factors affect the vibrational behavior of microtubules.

• 마이크로전자및패키징학회지
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• 제26권2호
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• pp.31-43
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• 2019

본 연구에서는 유연한 접속부를 갖는 유연전자 패키지 플립칩 접속을 위해 폴리머 탄성범프를 제작하였으며, 범프의 온도 및 하중에 따른 폴리머 탄성 범프의 점탄성 및 점소성 거동을 해석 및 실험적으로 분석하고 비교 평가하였다. 폴리머 탄성 범프는 하중에 의한 변형이 용이하여 범프 높이 평탄도 오차의 보정이 용이할 뿐만 아니라 소자가 형성된 칩에 가해지는 응력 집중이 감소하는 것을 확인하였다. 폴리머 탄성 범프의 과도한 변형에 따른 Au Metal Cap Crack 현상을 보완하여 $200{\mu}m$ 직경의 Spiral Cap Type, Spoke Cap type 폴리머 탄성 범프 형성 기술을 개발하였다. 제안된 Spoke Cap, Spiral Cap 폴리머 탄성 범프는 폴리머 범프 전체를 금속 배선이 덮고 있는 Metal Cap 범프에 비해 범프 변형에 의한 응력 발생이 적음을 확인할 수 있으며 이는 폴리머 범프 위의 금속 배선이 부분적으로 패터닝되어 있어 쉽게 변형될 수 있는 구조이므로 응력이 완화되는데 기인하는 것으로 판단된다. Spoke cap type 범프는 패드 접촉부와 전기적 접속을 하는 금속 배선 면적이 Spiral Cap type 범프에 비해 넓어 접촉 저항을 유지하면서 동시에 금속 배선에 응력 집중이 가장 낮은 결과를 확인하였다.

• Korea-Australia Rheology Journal
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• 제21권1호
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• pp.59-69
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• 2009

The prediction of pressure drop for a droplet flow in a confined micro channel is presented using FE-FTM (Finite Element - Front Tracking Method). A single droplet is passing through 5:1:5 contraction - straight narrow channel - expansion flow domain. The pressure drop is investigated especially when the droplet flows in the straight narrow channel. We explore the effects of droplet size, capillary number (Ca), viscosity ratio ($\chi$) between droplet and medium, and fluid elasticity represented by the Oldroyd-B constitutive model on the excess pressure drop (${\Delta}p^+$) against single phase flow. The tightly fitted droplets in the narrow channel are mainly considered in the range of $0.001{\leq}Ca{\leq}1$ and $0.01{\leq}{\chi}{\leq}100$. In Newtonian droplet/Newtonian medium, two characteristic features are observed. First, an approximate relation ${\Delta}p^+{\sim}{\chi}$ observed for ${\chi}{\geq}1$. The excess pressure drop necessary for droplet flow is roughly proportional to $\chi$. Second, ${\Delta}p^+$ seems inversely proportional to Ca, which is represented as ${\Delta}p^+{\sim}Ca^m$ with negative m irrespective of $\chi$. In addition, we observe that the film thickness (${\delta}_f$) between droplet interface and channel wall decreases with decreasing Ca, showing ${\delta}_f{\sim}Ca^n$ Can with positive n independent of $\chi$. Consequently, the excess pressure drop (${\Delta}p^+$) is strongly dependent on the film thickness (${\delta}_f$). The droplets larger than the channel width show enhancement of ${\Delta}p^+$, whereas the smaller droplets show no significant change in ${\Delta}p^+$. Also, the droplet deformation in the narrow channel is affected by the flow history of the contraction flow at the entrance region, but rather surprisingly ${\Delta}p^+$ is not affected by this flow history. Instead, ${\Delta}p^+$ is more dependent on ${\delta}_f$ irrespective of the droplet shape. As for the effect of fluid elasticity, an increase in ${\delta}_f$ induced by the normal stress difference in viscoelastic medium results in a drastic reduction of ${\Delta}p^+$.

• Tribology and Lubricants
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• 제36권1호
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• pp.1-10
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• 2020

Large-area two-dimensional (2D) materials synthesized by chemical vapor deposition on donor substrates are promising functional materials for conductors, semiconductors, and insulators in flexible and transparent devices. In most cases, 2D materials should be transferred from a donor substrate to a target substrate; however, 2D materials are prone to damage during the transfer process. The damages to 2D materials during transfer are caused by contamination, tearing, and chemical doping. For the commercialization of 2D materials, a damage-free, large-area, and productive transfer process is needed. However, a transfer process that meets all three requirements has yet to be developed. In this paper, we review the recent progress in the development of transfer processes for 2D materials, and discuss the principles, advantages, and limitations of each process. The future prospects of transfer processes are also discussed. To simplify the discussion, the transfer processes are classified into four categories: wet transfer, dry transfer, mechanical transfer, and electro-chemical transfer. Finally, the "roll-to-roll" and "roll-to-plate" dry transfer process is proposed as the most promising method for the commercialization of 2D materials. Moreover, for successful dry transfer of 2D materials, it is necessary to clearly understand the adhesion properties, viscoelastic behaviors, and mechanical deformation of the transfer film used as a medium in the transfer process.

• 지질공학
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• 제27권3호
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• pp.191-205
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• 2017

본 연구에서는 불투과형 사방댐과 링네트에 가해지는 충격하중을 평가하기 위해 토석류 모형축소실험을 수행하였다. 실험 결과, 토석류는 유체와 유사한 거동을 함에 따라 불투과형 사방댐 배면에 가해지는 토석류 충격하중은 하부구간이 4.14 kN로 가장 높게 작용하며 중간, 상부구간이 3.66 kN, 1.66 kN 가해지는 것으로 측정되었다. 링네트 실험결과 또한 불투과형 사방댐 결과와 같이 충격하중은 하부구간이 크며 상부로 갈수록 감소하는 경향을 보인다(2.28 kN, 1.95 kN, 1.49 kN). 수치해석 결과를 이용하여 토석류 흐름에 의한 토석류 방지시설 충격하중 흡수메커니즘을 분석한 결과, 불투과형 사방댐은 콘크리트 옹벽과 같이 구조물 자체의 강성을 이용하여 수평력에 저항하므로 실제 구조물에 작용한 수평력은 이론식과 유사한 결과가 제시되는 반면, 링네트는 강연선 탄성늘음과 네트 전면으로의 입자 투과를 이용하므로 충격하중은 사방댐 결과보다 최대 45% 감소하는 결과가 제시되었다.

• Steel and Composite Structures
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• 제34권5호
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• pp.643-655
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• 2020

In the present work, the buckling behavior of a single-layered graphene sheet (SLGS) embedded in visco-Pasternak's medium is studied using nonlocal four-unknown integral model. This model has a displacement field with integral terms which includes the effect of transverse shear deformation without using shear correction factors. The visco-Pasternak's medium is introduced by considering the damping effect to the classical foundation model which modeled by the linear Winkler's coefficient and Pasternak's (shear) foundation coefficient. The SLGS under consideration is subjected to compressive in- plane edge loads per unit length. The influences of many parameters such as nonlocal parameter, geometric ratio, the visco-Pasternak's coefficients, damping parameter, and mode numbers on the buckling response of the SLGSs are studied and discussed.