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Structural damping limits the free responses of a system, including both resonances and propagating waves. In this paper we review a number of important mechanisms by which structural damping may be achieved. These mechanisms have been called “macromechanisms” because there are identifiable elements or portions of the structure in which—by design—the dissipation of vibratory energy takes place.
Viscoelastic materials have found wide application in structural damping. Two important mechanisms of damping are those that utilize these materials in extensional and shear deformation—the so-called free and contrained viscoelastic layers, respectively. After discussing the characteristics of these mechanisms and the design parameters that govern their performance, we explore some of their modifications that are of practical interest. Also included is a discussion of thickness-resonance damping in viscoelastic layers applied to structures. Nonviscoelastic damping mechanisms that are considered briefly include friction damping and damping by granular media.
In summary we note that considerable progress has been made in damping technology in recent years. Rational design procedures and a broader selection of dissipative materials are becoming available. However, a number of unsolved problems remain in the areas of damping criteria and damping measurement.
Kerwin, E. M.
Senior consultant, Bolt Beranek and Newman, Inc., Cambridge, Mass.