Laser Doppler vibrometry-based measurements on viscoelastic panels for flexural damping properties

Abstract

Bending wave propagation is of central importance when enhancing sound transmission losses of sandwiched wall board systems incorporating viscoelastic panels as constrained damping layers. The damping properties of constrained damping layers made of viscoelastic materials can often be characterized by bending wave excitations. However, the multifactor, dispersive nature of the bending waves leads to challenges in reliable dynamic material characterization. To better understand the damping mechanism of the constrained damping layers, an experimental methodology employing complex bending wave theory has been developed to determine these flexural wave properties, including the loss factor and the bending stiffness of highly viscous panels. Relying on a transfer function from the experimentally measured bending velocities between two locations radially away from a flexural wave exciter on the viscoelastic panel under test, this methodology yields the broadband bending loss factor, the bending phase speed, and the bending stiffness. This paper discusses the experimental method for characterizing the above properties from laser Doppler vibrometry-based measurements of bending velocities. This paper also discusses the challenges with this method as well as an approach to mitigate the challenging effects and improve measurement accuracy.