Experimental study of embedded and non-embedded ordered granular chains under impulsive excitation

Experimental pulse transmission in impulsively loaded, homogeneous, and dimer granular chains, optionally embedded in a viscoelastic matrix, is studied. All tested chains are composed of spherical elastic beads of common radius. Homogeneous chains were composed of granules with equal mass, whereas dimer chains had alternating ‘heavy’ and ‘light’ granules with different masses. These media are strongly nonlinear due to Hertzian interactions between adjacent beads under compressive loads, and separations and collisions between them in the absence of compression. A series of experimental tests was performed to study primary pulse transmission in the non-embedded chains, and assess the effect of the surrounding viscoelastic matrix on pulse transmission in the embedded ones. For the case of dimer chains, the effect of mass inhomogeneity on pulse attenuation caused by scattering at the interfaces between adjacent beads is studied. In total, two embedded dimer chains, as well as an embedded homogeneous one, were manufactured and tested, and a previous theoretical model is used to compare theoretical predictions to experimental measurements. Whereas one of the non-embedded dimer chains differs from the others in that its light beads are hollow and so its experimental responses are not captured well by our theoretical model, for the other embedded and non-embedded chains, the theoretical predictions match remarkably well with the experimental measurements, despite the complexity in the acoustics induced by the surrounding matrix, and the conceptual simplicity of the theoretical model. The results of this work contribute to the development of practical acoustic metamaterials incorporating embedded granular media.