Microstructure design and experimental characterization of functional elastic metamaterials

Elastic metamaterials are of growing interest due to their dramatically increased manipulation ability as well as their novel engineering applications. The purpose of this research is to develop and model elastic metamaterials with unusual effective properties and their applications in low frequency elastic wave attenuation and vibration suppression. The working principle of the elastic metamaterials is to use man-made microstructures, local resonators, on a scale much less than its working wavelength. Therefore it is possible to describe their response by using dispersive homogenized effective media. First, we developed a retrieval method to obtain effective material properties of the metamaterial and a multi-displacement microstructure continuum model was introduced to investigate local resonance behavior inside the homogenized medium. Then, a thin elastic metamaterial plate with optimized periodic cantilever-mass microstructure was proposed and experimentally studied for wave attenuation applications for both low frequency in-plane and out-of-plane waves.;Anisotropic effective mass density in elastic metamaterial has been shown a great potential to control incident wave in various propagation directions, and also plays a key role in realization of elastic cloak. A new microstructure design of the elastic metamaterial plate was proposed to achieve strongly anisotropic effective mass density. The design was numerically analyzed and validated by developing a numerically based effective medium method to determine the anisotropic effective mass density. Furthermore, the special experimental setup was established to determine anisotropic effective mass density in an elastic metamaterial plate. Finally, a continuum plate model of the elastic metamaterial was developed to predict different guided wave modes which are difficult to measure experimentally. Interesting wave phenomena such as the wave coupling and repulsion as well as the preferential energy flow were discussed.;The bandgaps from many existing elastic metamaterials are of narrow bandwidth which limit their practical engineering applications. In the final chapter of this dissertation, we implemented both theoretical and experimental studies on a chiral-lattice-based elastic metamaterial beam with section distributed resonators for low frequency broadband vibration suppression. The chiral elastic metamaterial has excellent stiffness-to-weight ratio and is easily integrated with many existing engineering systems for both aerospace and civil engineering applications.