ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pSA10. The loss factor of beams with thick constrained layers.

Joel Garrelick

Cambridge Acoust. Assoc., Inc., 200 Boston Ave., Medford, MA 02155

A constrained layer beam, consisting of a base beam, viscoelastic layer, and cover plate, is analyzed with each layer modeled using the two-dimensional equations of viscoelasticity. The (three) layers are ``cascaded,'' enforcing appropriate equations of continuity. A shape factor is invoked to account for the effect of the beam's finite width on the dilatational wave speed of the constrained layer. Composite loss factors are first defined solely for the freely propagating (modified) flexural wave-number component of the response and then in terms of the overall drive point response of the beam to a mid-span load. At low frequencies results are compared to values obtained from Kerwin's [1959] classic thin layer model. At the other end, high frequency asymptotic limits are obtained by viewing the constrained layer as being semi-infinite and/or ``fuzzy.'' Finally, predictions are compared to measurements performed on a steel-Nitrile-steel beam [Junger et al., 1986].