Study of the effect of specimen size and frequency on the structural damping property of beam

It is said that the parameters that characterize structural damping, i.e., the loss factor, are identical to the material of the specimen, but in actuality, the damping property is sometimes affected by specimen size or the frequency. In this paper, we investigated the effect of specimen size and frequency on the structural damping property. First, we showed a simple identification method for modal parameters when the damping property is modeled as the structural damping. Next, we identify the modal parameters of the freely supported thin steel beam using the method. We obtain the relationship between the natural frequency and modal damping ratio for specimen with the same thickness but different length, and for specimen with the same length but different thickness. Then we identify the parameters that characterize the damping property. The results showed that the modal damping ratio was high in the lower frequency ranges, though light and constant in the higher frequency ranges, that is, the damping property depends on the frequency, so that the damping property could not be expressed only by the loss factor. And the relationship between the natural frequency and the modal damping ratio was identical for specimen with same thickness, though it is not for specimen with the different thickness, that is, the damping property depends on the thickness. We conclude that the effect of specimen size and frequency should be considered when predicting damping property in actual design processes