• Title, Summary, Keyword: Viscoelastic Layer

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Nonlinear vibration analysis of an electrostatically excited micro cantilever beam coated by viscoelastic layer with the aim of finding the modified configuration

  • Poloei, E.;Zamanian, M.;Hosseini, S.A.A.
    • Structural Engineering and Mechanics
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    • v.61 no.2
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    • pp.193-207
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    • 2017
  • In this study, the vibration of an electrostatically actuated micro cantilever beam is analyzed in which a viscoelastic layer covers a portion of the micro beam length. This proposed model is considered as the main element of mass and pollutant micro sensors. The nonlinear motion equation is extracted by means of Hamilton principle, considering nonlinear shortening effect for Euler-Bernoulli beam. The non-linear effects of electrostatic excitation, geometry and inertia have been taken into account. The viscoelastic model is assumed as Kelvin-Voigt model. The motion equation is discretized by Galerkin approach. The linear free vibration mode shapes of non-uniform micro beam i.e. the linear mode shape of the system by considering the geometric and inertia effects of viscoelastic layer, have been employed as comparison function in the process of the motion equation discretization. The discretized equation of motion is solved by the use of multiple scale method of perturbation theory and the results are compared with the results of numerical Runge-Kutta approach. The frequency response variations for different lengths and thicknesses of the viscoelastic layer have been founded. The results indicate that if a constant volume of viscoelastic layer is to be deposited on the micro beam for mass or gas sensor applications, then a modified configuration may be found by using the analysis of this paper.

An Experimental Study on Vibration Characteristics of Automotive Roof with Passive Constrained Layer Damping (수동구속감쇠층을 갖는 자동차루프의 진동특성에 대향 실험적 연구)

  • 이정균;김찬묵;강영규;사종성;홍성규
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.613-617
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    • 2004
  • This paper presents an experimental study on vibration characteristics of an automotive roof with viscoelastic material. The goal of the study is to extract modal parameters (natural frequency, loss factor, and mode shape) of automotive roof with unconstrained and constrained layer damping treatment. To determine the effective position of the viscoelastic patch on a roof, vibration tests have been carried out for two cases; Aluminum plate with viscoelastic patch on maximum strain energy, and aluminum plate with viscoelastic patch on nodal line. From the result of aluminum plate, it is found that the viscoelastic patch should be attached on the Place with maximum strain energy Part. For the automotive root five Patches of unconstrained or constrained viscoelastic material have been attached on the position of maximum strain energy. This paper addresses that the proper position of viscoelastic patch is very important and the concept of maximum strain energy may be a good criterion f3r the placement of viscoelastic patch.

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Optimal Layout Design of Frequency- and Temperature-Dependent Viscoelastic Materials for Maximum Loss Factor of Constrained-Layer Damping Beam (점탄성 물질의 온도와 주파수 의존성을 고려한 구속형 제진보의 최대 손실계수 설계)

  • Lee, Doo-Ho
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.1023-1026
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    • 2007
  • Optimal damping layout of the constrained viscoelastic damping layer on beam is identified with temperatures by using a gradient-based numerical search algorithm. An optimal design problem is defined in order to determine the constrained damping layer configuration. A finite element formulation is introduced to model the constrained damping layer beam. The four-parameter fractional derivative model and the Arrhenius shift factor are used to describe dynamic characteristics of viscoelastic material with respect to frequency and temperature. Frequency-dependent complex-valued eigenvalue problems are solved by using a simple resubstitution algorithm in order to obtain the loss factor of each mode and responses of the structure. The results of the numerical example show that the proposed method can reduce frequency responses of beam at peaks only by reconfiguring the layout of constrained damping layer within a limited weight constraint.

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A Study on Dynamic Characteristics of Single Lap Joints with Different Joining Methods (체결방법에 따른 랩조인트의 동특성 해석)

  • Jung, Y.D.;Park, M.K.;Bahk, S.M.;Choi, Y.S.
    • Proceedings of the KSME Conference
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    • pp.624-629
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    • 2001
  • Two types of bolted lap joints, one with a viscoelastic layer and the other without the viscoelastic layer were chosen to analyze the dynamic characteristics of the joints with the mechanical properties of the bolts of the joints being taken as computational variables. The finite element method was used along with the impact hammer technique to verify the FEM model. The results in the bolted lap joints reveal that the higher the Young's Modulus for the bolts are the higher the natural frequencies results for the joints. However, the natural frequency differences in the first and second mode are not substantial but become noticeable in the higher modes. Lower natural frequencies were obtained for the bolted lap joints with the viscoelastic layer when compared with those of the bolted lap joints without the viscoelastic layer. And the differences in the natural frequencies for the two types of joints are relatively small in the first and second mode whereas in the higher mode the differences become significant. The loss factors were observed to be significant especially in the second mode for the bolted lap joints with the viscoelastic layer.

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An Analysis of Dynamic Characteristics of Bolted Lap Joints with Viscoelastic Layers (점탄성재 삽입시 볼트랩 죠인트의 동특성 해석)

  • 박명균;박세만;최영식;박상규
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.1
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    • pp.172-178
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    • 2003
  • Two types of bolted lap joints, one with a viscoelastic layer and the other without the viscoelastic layer were chosen to analyze the dynamic characteristics of the joints with the mechanical properties of the bolts in the joints are considered as computational variables. The finite element method was used along with the modal testing to verify the PEM model. The results in the bolted lap joints reveal that the higher the Young's modulus for the bolts we use the higher the natural frequencies we obtain fur the joints. However, the natural frequency differences in the first and second mode are not substantial but become noticeable in the higher modes. Lower natural frequencies were obtained for the bolted lap joints with the viscoelastic layer when compared with those of the bolted lap joints without the viscoelastic layer. And the differences in the natural frequencies for the two types of joints are relatively small in the first and second mode whereas in the higher mode the differences become significant. The loss factors were observed to be significant especially in the second mode for the bolted lap joints with the viscoelastic layer.

Behavior of the Flexural Vibration of a Sandwich Beam with Partially Inserted Viscoelastic Layer (점탄성층이 부분적으로 삽입된 샌드위치보의 횡진동 특성)

  • 박진택;최낙삼
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.167-170
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    • 2000
  • The flexural vibration of a sandwich beam with partially inserted viscoelastic layer has been studied using the finite element analysis in combination with an experiment. Effects of length and thickness of partial viscoelastic layers on system loss factor(${\eta}_s$) and resonant frequency(${\omega}_r$) were considerably large. The thicker the viscoelastic layer in a sandwich beam, the larger the system loss factor in Mode 1 as compared with that in Mode 2. The loss factor increased almost linearly with increasing the length of partial viscoelastic layer. Effects of thickness of beams were also considered.

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Length Optimization for Unconstrained Visco-elastic Damping Layer of Beams (비구속형 점탄성 제진층을 갖는 보의 제진층 길이 최적화)

  • 이두호;황우석
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.665-671
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    • 2003
  • Length of an unconstrained viscoelastic damping layer on beams is determined to maximize loss factor using a numerical search method. The fractional derivative model can describe damping characteristics of the viscoelastic damping material, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kerwin(RUK) equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are obtained with respect to ambient temperatures and thickness ratios of beam and damping layer.

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Vibration and Damping Characteristics of Viscoelastically Damped Sandwich Plates (점탄성층이 샌드위치된 복합적층판의 진동감쇠 특성)

  • 김재호;박태학;신현정
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.9
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    • pp.2252-2263
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    • 1993
  • The purpose of this study is to verify the vibration and damping characteristics of elastic-viscoelastic-elastic structures, theoretically and experimentally. The forth-order differential equations of motion are derived for the transverse vibration of three-layered plates with viscoelastic core layer. The equations consider both transverse displacements of the constraining layer and the bare base plate as variable and account for the effect of the transverse normal strain and the shear strain of viscoelastic core layer on the vibration of the plates. Finite difference analysis of the equations and experimental measurements are performed on the three-layered plates of completely free boundary condition. Comparative investigations on the theory and the results of direct frequency analysis of NASTRAN are carried out on the same structures.

Length Optimization for Unconstrained Visco-elastic Damping Layer of Beams (비구속형 점탄성 제진층을 갖는 보의 제진층 길이 최적화)

  • Lee, Doo-Ho;Hwang, Woo-Seok
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.13 no.12
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    • pp.938-946
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    • 2003
  • Length of an unconstrained viscoelastic damping layer on beams is determined to maximizeloss factor using a numerical search method. The fractional derivative model can describe damping characteristics of viscoelastic damping materials accurately, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kelvin[RUK] equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are identified with ambient temperatures and thickness ratios of beam and damping layer by using a finite-difference-based steepest descent method.

Torsional surface waves in a non-homogeneous isotropic layer over viscoelastic half-space

  • Kakar, Rajneesh;Gupta, Kishan Chand
    • Interaction and multiscale mechanics
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    • v.6 no.1
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    • pp.1-14
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    • 2013
  • The aim of this paper is to study the propagation of torsional surface waves in non-homogeneous isotropic layer of finite thickness placed over a homogeneous viscoelastic half-space, when both density and rigidity of the non-homogeneous medium are assumed to vary exponentially with depth. The frequency equations are obtained by using simple method of separation of variables. Further, it is seen that when viscoelastic parameter and non-homogeneity parameter is neglected, the dispersion equation gives the dispersion equations of Love waves in homogeneous, elastic and isotropic layer placed over homogeneous viscoelastic medium. The problem has been solved numerically and the effects of various inhomogeneities of the medium on torsional waves have been illustrated graphically.