Finding damping loss factor using circle-fit method on Nyquist diagrams.

Viscoelastic materials are commonly applied into vehicles sheet metal structures including the roof and doors in order to increase the amount of structural damping. The added damping from viscoelastic materials dissipates a greater amount of vibrational energy, subsequently reducing vibration displacement, structure borne noise, and energy flow to adjacent structures. Because damping treatments have the disadvantage of adding weight to the treated structure, adequate tools to characterize and evaluate their efficiency are necessary. In this paper, natural frequencies and modal damping are determined by applying circle-fit interpolation to measured data. Comparison to traditional peak picking and half-power point methods shows that this geometric approach allows modal frequencies to be identified more clearly, even for measurement systems with reduced frequency resolution and the process can be easily automated.