Abstract:
Studies on a useful and rarely used damping technique, the filling of cavity components with granular materials, are presented. Experimental studies show regions of maximum damping caused by standing wave formation in the material. The first maximum occurs when the internal dimension of the cavity is equal to one quarter of the longitudinal wavelength. The tuning of optimum damping to any desirable frequency requires accurate knowledge of the wave speed. Experiments show that wave speeds decrease with amplitude when strains reach values higher than about 10[sup -6]. This is caused by gross slip taking place at contacts which breaks the main structure of grain--grain contacts responsible for the propagation of elastic waves. Waves speed whose amplitude produce strain smaller than 10[sup -6] were observed being independent of amplitude. Loss factors of granular materials also present identical variation with strain. At large strains (>10[sup -6]) energy is mainly dissipated at grain contacts, by dry friction in partial and gross slip forms. For low strains, energy is dissipated by hysteresis inside the grains themselves. Applications of this technique to heavy structures are useful.