  We report the design and testing of a tunable and nonlinear mechanical
metamaterial, called locally resonant granular chain. It consists of a
one-dimensional array of hollow spherical particles in contact, containing
local resonators. The resonant particles are made of an aluminium outer
spherical shell and a steel inner mass connected by a polymeric plastic
structure acting as a spring. We characterize the linear spectra of the
individual particles and of one-dimensional arrays of particles using theory,
numerical analysis, and experiments. A wide band gap is observed as well as
tunability of the dispersive spectrum by changing the applied static load.
Finally, we experimentally explore the nonlinear dynamics of the resonant
particles. By using nonlinear acoustical techniques, we reveal a complex,
nonclassical nonlinear dynamics.
