Georgios Theocharis (Laboratoire d'Acoustique de l'Université du Maine, Le Mans). Complex Dynamics of Granular Chains: from wave guiding (ordered) to localisation and shocklike superdiffusion (disordered).

Granular solids are dense packings of elastic particles. These materials are of substantial importance in many industrial and natural processes and they also offer a perfect test bed for new insights into problems in glassy physics and elastic metamaterials. In the first part of this seminar, I will focus on the wave propagation in mono-disperse (ordered) granular chains. This theoretical and experimental study is based on the conceptually new design of phononic crystals composed of a chain of stainless steel spherical beads in contact, under a suitable designed magnetic field. In the second part, I will present our theoretical and numerical studies on energy transport in polydispersed (disordered) granular chains. By increasing the initial excitation amplitudes we are able to identify three distinct dynamical regimes with different energy transport properties: a near linear, a weakly nonlinear and a highly nonlinear regime. We demonstrate that chaos is responsible for destruction of energy localisation and that in the highly nonlinear regime, the energy is almost ballistically transported through shock-like excitations.