Mechanisms and Measurement of Structural Damping

The first part of this paper presents a brief review of some common mechanisms of structural damping in beams and plates. The mechanisms reviewed involve dissipation in viscoelastic materials, specifically in the so-called free and constrained viscoelastic layers, and the thickness-resonant viscoelastic layer. In each case, the parameters governing damping effectivness are defined, and the dependence of damping on these parameters is discussed. Radiation damping is also reviewed briefly. In the second part of the paper, some of the problems encountered in determining the damping of complex systems are discussed. Such problems are found where the damping is moderate or high, or where the system is extensive or involves coupled subsystems. Important considerations here are the distribution of vibrating energy throughout the system, the degree of coupling among subsystems, and the type of vibratory excitation. Some damping measurements in complex structures are discussed. Preliminary guides for performing damping measurements in complex systems are given.