The influence of the support condition of a beam of a sandwich plate on the modal loss factor is examined. Resonant frequency and modal loss factor are calculated based on Mead's theory. While Ungar's equation, which is generally employed to estimate loss factor, is valid only for a simply supported beam, a trial of applying it to other support conditions is performed by defining the equivalent half-wavelength, and it is suggested that for support conditions other than simply supported as well, resonant frequency is well predicted by Ungar's equation. Only for the simply supported beam, can the modal loss factor be determined uniquely from frequency. For other general support conditions, loss factor depends on the mode order. An experiment is performed with the support condition of both ends simply supported and free, and a similar tendency to these finding is shown. It was demonstrated that the loss factor obtained from antiresonance for symmetrically supported beams corresponds to the modal loss factor for the clamped beam of half length. This is also verified experimentally.
