The forced vibration of a three-layer, damped sandwich beam with arbitrary boundary conditions

http://research.me.mtu.edu/abstracts/Rao-%20Recent%20Applications%20of%20Viscoelastic%20Damping%20for%20Noise%20Control%20in%20Automobiles%20and%20Commercial%20Airplanes.pdf

Recent applications of viscoelastic damping for noise control in automobiles and commercial airplanes

The present review aims at gathering the available literature on damping in composite materials. A chronological review of test methods for damping estimation is presented in order to describe the time-line of the theoretical knowledge development in this field. In the last years many new material configurations have emerged that deserve investigation, such as nano-composites, hybrid laminates and sandwich materials. Damping models specifically meant for non-homogeneous materials are reported to provide a background for understanding this problem. Although not widely exploited yet, fibre reinforced polymers has the potential to be tailored for damping by acting on constituents, geometry and boundary conditions. Nano-composites, for instance, are shown to possess a high potential for damping purposes. New hybrid and sandwich-type structures are emerging as noise and vibration control solutions in lightweight applications. The effort devoted to mathematical and numerical model in view of Finite Element integration of damping properties is also addressed. Finally, the conclusions summarise the ideas of the authors on needed steps to advance the state-of-the-art in each of the described topic.

Damping in composite materials: Properties and models

Analytical modeling of viscoelastic dampers for structural and vibration control

Review and assessment of various theories for modeling sandwich composites

For a number of years it has been known that flexural vibrations in a plate can be damped by the application of a layer of damping (viscoelastic) material that is in turn constrained by a backing layer or foil. A common example is the damping tape currently used in aircraft.This paper presents a quantitative analysis of the damping effectiveness of such a constrained layer. As in the work of H. Oberst the damping is characterized by the loss factor η, which is the normalized imaginary part of the complex bending stiffness of the damped plate.The calculated damping factor depends on the wavelength of bending waves in the damped plate, and on the thicknesses and elastic moduli of the plate, the damping layer, and the constraining layer. A complex shear modulus is assigned to the damping layer, where all of the energy dissipation is assumed to take place.Damping factors have been determined experimentally on laboratory test bars for a number of constrained‐damping‐layer applications for frequencies from abou...

Damping of Flexural Waves by a Constrained Viscoelastic Layer

Two important treatments for the damping of flexural waves in plates are the free viscoelastic layer [H. Oberst, Acustica 2, Suppl. 4 (1952)] and the constrained viscoelastic layer, sometimes called “damping tape” [E. M. Kerwin, Jr., J. Acoust. Soc. Am. 31, 952 (1959)]. In this paper we compare these two treatments in order to determine which is more useful in a given situation. For good, contemporary damping materials at lower treatment weights, and therefore lower values of damping, the constrained layer is the more effective. The free layer becomes more effective than the constrained layer for higher treatment weights. At a given fraction of the plate weight, the performance of a given free layer depends on the plate material (e.g., steel vs aluminum). On the other hand, if the constraining layer has the same modulus‐to‐density ratio as the plate material, the maximum effectiveness of a constrained layer at a given fraction of the plate weight is practically independent of the plate material. (This wor...

Comparison of the Vibration Damping Effectiveness of Free and Constrained Viscoelastic Layers

Layers of viscoelastic material are useful in the damping of flexural waves in plates. Two basic damping treatments using such layers are the homogeneous damping layer analyzed by Oberst [Akust. Beih. 4 (1952)] and the constrained damping layer analyzed by the author [J. Acoust. Soc. Am. 30, 698 (1958)]. In these treatments the viscoelastic layer is distorted in extension and shear, respectively. In the present paper we show that with both basic treatments, the insertion of a “spacer” layer between the plate and the damping treatment serves to magnify the distortion of the damping material, thus increasing the damping factor. The ideal spacer should be incompressible and infinitely stiff in shear. Its extensional stiffness in a plane parallel to the plane of the plate should be negligible. We treat the case of spaced damping treatments with ideal spacers, showing the increase in damping as a function of spacer thickness. Significant increases in damping factor are found, amounting to a factor of 10 or more in some cases. Some measured damping factors are presented for treatments with and without spacers.

Ideal Spaced Damping Treatments for Flexural Waves

For a number of years it has been known that bending vibrations in a plate can be damped by the application of a layer of damping (viscoelastic) material that is in turn stiffened or constrained by a backing layer or foil. A common example is the damping tape currently used in aircraft. This paper presents a quantitative analysis of the damping effectiveness of such a stiffened layer. As in the work of H. Oberst (e.g., in Akust. Beth., 1952, 1954, 1956) the damping is characterized by the loss factor, η, which is the normalized imaginary part of the complex bending stiffness of the damped plate. The calculated damping factor depends on the wavelength of bending waves in the damped plate, and on the thicknesses and elastic moduli of the plate, the damping layer, and the stiffener. A complex shear modulus is assigned to the damping layer, where all of the energy dissipation is assumed to take place. Damping factors have been determined experimentally on laboratory test bars for a number of stiffened damping...

Edward M. Kerwin

Papers

Damping of Flexural Waves by a Constrained Viscoelastic Layer

Comparison of the Vibration Damping Effectiveness of Free and Constrained Viscoelastic Layers

Ideal Spaced Damping Treatments for Flexural Waves

Vibration Damping by a Stiffened Damping Layer