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Research Papers

Optimal Damping in Circular Cylindrical Sandwich Shells With a Three-Layered Viscoelastic Composite Core

[+] Author and Article Information
Ambesh Kumar

Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati 781039, India

Satyajit Panda

Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati 781039, Assam, India
e-mail: spanda@iitg.ernet.in

1Corresponding author.

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received December 12, 2016; final manuscript received April 30, 2017; published online July 26, 2017. Assoc. Editor: Stefano Gonella.

J. Vib. Acoust 139(6), 061003 (Jul 26, 2017) (12 pages) Paper No: VIB-16-1589; doi: 10.1115/1.4036868 History: Received December 12, 2016; Revised April 30, 2017

In this work, the damping characteristics of circular cylindrical sandwich shell with a three-layered viscoelastic composite core are investigated. The new composite core is composed of the identical inclusions of graphite-strips which are axially embedded within a cylindrical viscoelastic core at its middle surface. The physical configuration of the composite core is attributed in the form of a cylindrical laminate of two identical monolithic viscoelastic layers over the inner and outer cylindrical surfaces of middle viscoelastic composite layer so that it is a three-layered viscoelastic composite core. A finite element (FE) model of the overall shell is developed based on the layerwise deformation theory and Sander's shell theory. Using this FE model, the damping characteristics of the shell are studied within an operating frequency range after configuring the size and circumferential distribution of graphite-strips in optimal manner. The numerical results reveal significantly improved damping in the sandwich shell for the use of present three-layered composite core instead of traditional single-layered viscoelastic core. It is also found that the three-layered core provides the advantage in achieving damping at different natural modes as per their assigned relative importance while it is impossible in the use of single-layered viscoelastic core.

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Figures

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Fig. 1

Schematic diagrams of (a) sandwich shell with single-layered viscoelastic core, (b) sandwich shell with three-layered viscoelastic composite core, and (c) layers of three-layered viscoelastic composite core

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Fig. 2

Verification of present FE formulation (m and n are the longitudinal and circumferential mode numbers, respectively)

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Fig. 3

Mode shape (m=1, n=4) over the circumference of the shell for (a) single-layered/(d) three-layered core; distributions of εy for (b) single-layered/(e) three-layered core; distributions of εyz for (c) single-layered/(f) three-layered core

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Fig. 4

Variations of modal loss factors (η/ηs/ηe) with the thickness (hc) of single-layered viscoelastic core of (a) unsymmetrical (hfb= 4 mm, hft= 0.2 mm) and (b) symmetrical (hfb=hft= 2 mm) sandwich shells

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Fig. 5

Variations of modal loss factors (η/ηs/ηe) with the thickness of VCM layer (αv=0.01  deg, nf=72) for (a) and (b) unsymmetrical and (c) and (d) symmetrical sandwich shells

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Fig. 6

Variations of modal loss factors (η/ηs/ηe) with the circumferential gap (αv in deg) in the VCM layer for (a) unsymmetrical (rc = 0.8, nf=72) and (b) symmetrical (rc = 0.7, nf = 72) sandwich shells

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Fig. 7

Variations of modal loss factors (η/ηs/ηe) with the number (nf) of graphite-strips within the VCM layer for (a) unsymmetrical (rc = 0.8, αv=0.01 deg) and (b) symmetrical (rc = 0.7, αv=0.01  deg) sandwich shells

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Fig. 8

Frequency responses of the (a) unsymmetrical and (b) symmetrical cylindrical sandwich shells composed of single-layered viscoelastic core

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Fig. 10

(a) Variation of η¯ for symmetrical sandwich shell at different grid points of 3D mesh with the axial directions of rc, αv, nf and (b) contour plot for variation of η¯ in 2D plane of rc and nf at αv=0.01  deg (M-point for maximum η¯)

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Fig. 9

(a) Variation of η¯ for unsymmetrical sandwich shell at different grid points of 3D mesh with the axial directions of rc, αv, nf and (b) contour plot for variation of η¯ in two-dimensional (2D) plane of αv and nf at rc= 0.85 (M-point for maximum η¯)

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Fig. 11

Frequency responses of the (a) unsymmetrical and (b) symmetrical sandwich shells either composed of single-layered core or composed of three-layered core (modes with m = 1)

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