• Title/Summary/Keyword: viscoelastic properties

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Dynamic load concentration caused by a break in a Lamina with viscoelastic matrix

  • Reza, Arash;Sedighi, Hamid M.;Soleimani, Mahdi
    • Steel and Composite Structures
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    • v.18 no.6
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    • pp.1465-1478
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    • 2015
  • The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower.

Hybrid Modelling of Soil-Structure System on Viscoelastic Soil Medium (복합모형을 이용한 점탄성지반의 지반-구조물 상관관계)

  • Hong, Kyu Seon;Yun, Chung Bang
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.6 no.1
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    • pp.35-41
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    • 1986
  • A hybrid modelling technique of a soil-structure system on viscoelastic soil medium is studied in this paper. The hybrid model consists of a near-field and a far-field with their common interface passing through the soil region at some distance from the base of the structure. It makes use of frequency-dependent impedances so as to represent the semi-infinite far-field. The far-field impedances are formulate including the radiation damping characteristics as well as the viscoelastic properties of the soil medium. The verification of the method has been carried out using a rigid circular plate on a viscoelastic half-space. The impedances obtained by the method are compared with the theoretical values. Example analyses have been performed for a tall chimney and the results have been compared with those obtained by other methods which are frequently used.

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Vibration Test of a Full-Scale Five-Story Structure with Viscoelastic Dampers: Damper Design and Test for Response (점탄성 감쇠기가 설치된 실물크기 5층 건물의 진동실험: 감쇠기의 설계 및 응답실험)

  • 민경원;이상현;김진구;이영철;이승준;김두훈
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.3
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    • pp.9-15
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    • 2003
  • This paper presents a design procedure for viscoelastic dampers to be installed in a full-scale steel structure and observes their vibration control effect, based on the excitation method and the dynamic characteristics of the structure investigated in the companion paper, Additional damping ratios required to reduce the maximum displacement to a given level were obtained by convex model. The size of dampers was determined by observing the change in modal damping ratio due to the change in damper stiffness using the modal strain energy method, The effect of the supporting braces was also considered in the determination of the modal properties. Two viscoelastic dampers were installed at the first and second inter-stories, respectively and their response reduction is verified.

Dynamic Response Analysis of Rotating Composite-VEM Thin-Walled Beams Incorporating Viscoelastic Materials in the Time Domain

  • Na Sung-Soo;Park Jae-Yong;Park Chul-H.;Kwak Moon-K.;Shim Jae-Hong
    • Journal of Mechanical Science and Technology
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    • v.20 no.8
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    • pp.1139-1148
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    • 2006
  • This paper addresses the analytical modeling and dynamic response of the advanced composite rotating blade modeled as thin-walled beams and incorporating viscoelastic material. The blade model incorporates non-classical features such as anisotropy, transverse shear, rotary inertia and includes the centrifugal and coriolis force fields. The dual technology including structural tailoring and passive damping technology is implemented in order to enhance the vibrational characteristics of the blade. Whereas structural tailoring methodology uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The case of VEM spread over the entire span of the structure is considered. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on the dynamic response of a rotating thin-walled b ε am exposed to external time-dependent excitations.

Predictive Study of Rubber Friction Considering Large Deformation Contact (대변형 접촉을 고려한 고무 마찰 예측 연구)

  • Nam, Seungkuk
    • Tribology and Lubricants
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    • v.34 no.1
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    • pp.1-8
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    • 2018
  • This paper presents the analysis of friction master curves for a sliding elastomer on rough granite. The hysteresis friction is calculated using an analytical model that considers the energy spent during the local deformation of the rubber due to surface asperities. The adhesion friction is also considered for dry friction prediction. The viscoelastic modulus of the rubber compound and the large-strain effective modulus are obtained from dynamic mechanical analysis (DMA). We accurately demonstrate the large strain of rubber that contacts with road substrate using the GW theory. We found that the rubber block deforms approximately to 40% strain. In addition, the viscoelastic master curve considering nonlinearity (at 40% strain) is derived based on the above finding. As viscoelasticity strongly depends on temperature, it can be assumed that the influence of velocity on friction is connected to the viscoelastic shift factors gained from DMA using the time-temperature superposition. In this study, we apply these shift factors to measure friction on dry granite over a velocity range for various temperatures. The measurements are compared to simulated hysteresis and adhesion friction using the Kluppel friction theory. Although friction results in the low-speed band match well with the simulation results, there are differences in the predicted and experimental results as the velocity increases. Thus, additional research is required for a more precise explanation of the viscoelastic material properties for better prediction of rubber friction characteristics.

Three dimensional dynamic response of functionally graded nanoplates under a moving load

  • Hosseini-Hashemi, Shahrokh;Khaniki, Hossein Bakhshi
    • Structural Engineering and Mechanics
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    • v.66 no.2
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    • pp.249-262
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    • 2018
  • In this paper, reaction of functionally graded (FG) thick nanoplates resting on a viscoelastic foundation to a moving nanoparticle/load is investigated. Nanoplate is assumed to be thick by using second order shear deformation theory and small-scale effects are taken into account in the framework of Eringen's nonlocal theory. Material properties are varied through the thickness using FG models by having power-law, sigmoid and exponential functions for material changes. FG nanoplate is assumed to be on a viscoelastic medium which is modeled using Kelvin-Voight viscoelastic model. Galerkin, state space and fourth-order Runge-Kutta methods are employed to solve the governing equations. A comprehensive parametric study is presetned to show the influence of different parameters on mechanical behavior of the system. It is shown that material variation in conjunction with nonlocal term have a significant effect on the dynamic deformation of nanoplate which could be used in comprehending and designing more efficient nanostructures. Moreover, it is shown that having a viscoelastic medium could play an important role in decreasing these dynamic deformations. With respect to the fresh studies on moving atoms, molecules, cells, nanocars, nanotrims and point loads on different nanosctructures using scanning tunneling microscopes (STM) and atomic force microscopes (AFM), this study could be a step forward in understanding, predicting and controlling such kind of behaviors by showing the influence of the moving path, velocity etc. on dynamic reaction of the plate.

Dynamic stability analysis of a rotary GPLRC disk surrounded by viscoelastic foundation

  • Liang, Xiujuan;Ji, Haixu
    • Geomechanics and Engineering
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    • v.24 no.3
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    • pp.267-280
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    • 2021
  • The research presented in this paper deals with dynamic stability analysis of the graphene nanoplatelets (GPLs) reinforced composite spinning disk. The presented small-scaled structure is simulated as a disk covered by viscoelastic substrate which is two-parametric. The centrifugal and Coriolis impacts due to the spinning are taken into account. The stresses and strains would be obtained using the first-order-shear-deformable-theory (FSDT). For Poisson ratio, as well as various amounts of mass densities, the mixture rule is employed, while a modified Halpin-Tsai model is inserted for achieving the elasticity module. The structure's boundary conditions (BCs) are obtained employing GPLs reinforced composite (GPLRC) spinning disk's governing equations applying principle of Hamilton which is based on minimum energy and ultimately have been solved employing numerical approach called generalized-differential quadrature-method (GDQM). Spinning disk's dynamic properties with different boundary conditions (BCs) are explained due to the curves drawn by Matlab software. Also, the simply-supported boundary conditions is applied to edges 𝜃=𝜋/2, and 𝜃=3𝜋/2, while, cantilever, respectively, is analyzed in R=Ri, and R0. The final results reveal that the GPLs' weight fraction, viscoelastic substrate, various GPLs' pattern, and rotational velocity have a dramatic influence on the amplitude, and vibration behavior of a GPLRC rotating cantilevered disk. As an applicable result in related industries, the spinning velocity impact on the frequency is more effective in the higher radius ratio's amounts.

Electric Properties of LB Films using Impedance Analysis of Quartz Crystal (수정진동자의 임피던스 해석에 의한 LB막의 전기적 특성)

  • Jin, Cheol-Nam;Kim, Gyeong-Hwan;Yu, Seung-Yeop;Gwon, Yeong-Su
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.48 no.7
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    • pp.503-507
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    • 1999
  • Quartz crystal in contact with viscoelastic medium was described directly in terms of the electrical equivalent circuit of the system. Stearic acid was used as viscoelastic medium and deposited on the surface of quartz crystal using the Langmuir-Blodgett(LB) method. Impedance properties of quartz crystal coated with LB films which were investigated by using admittance diagram and $Ζ-\theta$ plot a method of impedance analysis. When stearic acid LB film was deposited on the surface of quartz crystal, resonant frequency of quartz crystal was changed about 100 Hz/layer. This result illustrates the ability of the sensor system to detect small amounts of special gas in air.

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Studies on Rheological Properties of High Solids Coating Colors (I) - Effect of Rheology Modifiers on Viscoelastic Properties -

  • Yoo, Sung-Jong;Cho, Byoung-Uk;Lee, Yong-Kyu
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.44 no.5
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    • pp.39-45
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    • 2012
  • For a fundamental study for high concentration pigment coating, the effects of alkali swellable emulsion (ASE) type rheology modifier and surface adsorption emulsion (SAE) type rheology modifier on both the stability and the viscoelastic behavior of a coating color were elucidated. The coating color prepared with SAE type rheology modifier showed superior thermal and mechanical stability than that with ASE type. In the high concentration and high speed coating process, the mechanical stability of a coating color was a key parameter since both impact force and shear force were increased with the increase of coating color concentration and coating speed, respectively.

The Impedance Properties of Quartz Crystal Microbalance Coated with LB films (LB막을 누적한 수정진동자의 임피던스 특성)

  • 진철남;김경환;유승엽;박재철;권영수
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1998.11a
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    • pp.171-174
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    • 1998
  • Quartz crystal in contact with viscoelastic medium is described directly in terms of the electrical equivalent circuit of the system. Stearic acid is used as viscoelastic medium and deposited on the surface of quartz crystal using the Langmuir-Blodgett(LB) method. Impedance properties of quartz crystal coated with LB films which were investigated and the possibility of applying the technique to chemical sensing introduced.

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