Propagation of longitudinal waves in the broadband hybrid mechanism gradient elastic metamaterials rods

In this work, a novel broadband hybrid mechanism gradient Elastic Metamaterials (EMs) rod, based on traditional formation mechanisms of band gaps, is proposed and the vibration suppression characteristics are estimated by calculating the transmission frequency response function (TRFPF) of the elastic wave propagation in the composite structure. The idea of gradient construction was first introduced in the traditional EMs rods, including the Bragg Elastic Metamaterials (BEMs) and the Local Resonance Elastic Metamaterials (LREMs), and the vibration attenuation performance of the gradient EMs rods was investigated. Subsequently, the Hybrid Elastic Metamaterials (HEMs) were constructed, based on the two former traditional (BEMs and LREMs) EMs, and the suppression mechanism of elastic waves and the effects of the key material parameters on the band gaps were further elaborated. The related results well confirm that the gradient BEMs rod and the gradient LREMs rod, with the distributed local resonators, both illustrated wider vibration attenuation regions and larger damping amplitudes, when compared to the conventional EMs rods (i.e. Phononic Crystal, PC). In the case of gradient HEMs rods, with the gradient change filling rate and local resonator, both showed a better vibration absorbing performance, as the vibration attenuation frequency range can be broadened by 7.34%. The relevant investigations of the longitudinal wave propagation in various gradient EMs rods as well as the corresponding construction methods would provide a novel way for the low-frequency broadband vibration absorption in practical engineering applications.