MEASUREMENT OF COMPLEX SHEAR MODULUS OF VISCOELASTIC MATERIALS BY MECHANICAL IMPEDANCE METHODS

The analytical prediction of damping performance as a function of frequency for laminated elastic-viscoelastic -elastic beams has been quite accurately carried out by several investigators by assuming previous knowledge of dimensions, constants of elastic materials, and dynamic shear parameters of viscoelastic materials. One investigation has shown vast differences in the results of measurements of dynamic shear modulus of the same viscoelastic materials by different facilities. To increase the accuracy of analytical predictions of structural damping in U. S. Navy ships, there is a need for accurate measurement of complex shear modulus. This report describes an experimental method which uses mechanical impedance measurements on a laminated sandwich beam with a viscoelastic layer that is thin compared to the elastic layers to measure the complex shear modulus of the viscoelastic material. Results of using the method show that it provides an accurate and repeatable measurement. (Author)