Unveiling the key role of interfaces in the design of finite-sized metamaterial structures

This paper investigates the influence of interfaces on the performance of finite-sized mechanical metamaterial structures for vibration damping applications. The metamaterial structures are designed in a sandwich configuration in which two homogeneous plates are connected to a metamaterial array. We test four different arrays that are obtained from the same metamaterial by differently cutting the metamaterial’s unit cell at the metamaterial/plate interface. When the four unit cells are periodically repeated in space, they create the same infinitely large metamaterial with an identical mechanical response. In finite-sized structures, however, the different interfaces between the metamaterial array and the plates – called “material interfaces” – and between the metamaterial and the air – called “free interfaces” – strongly affect the specimen’s vibration transmission characteristics. Using experimental measurements and validated finite-element (FE) models, we demonstrate a significant influence of the different types of interfaces on the global responses and local displacement fields of the structures. We also demonstrate the presence of a vibroacoustic coupling in the structures which also depends on the type of metamaterial/plate interfaces. Furthermore, we explore optimization strategies for enhancing the vibration damping performance of the metamaterial structures considering not only the metamaterial array but also the adjacent structures, i.e. the homogeneous plates. A comparison with benchmark cases clearly illustrates the optimization potential that the interfaces’ design offers for the vibration damping capability of finite-sized metamaterial structures. We show that optimizing the type of targeted interfaces can shift a given metamaterial’s response from underperforming to significantly outperforming compared to classical solutions for noise and vibration damping in civil engineering. • Using a selected example of a composed metamaterial structure, we prove the influence of material interfaces and free interfaces on the behavior of the targeted metamaterial structure experimentally and in numerical simulations. • We show in detail how different types of interfaces influence the wave propagation in the metamaterial by comparing the local displacement fields of specimens which provide different boundary conditions and by assessing the resulting global dynamic behavior. • We analyze different factors that influence the behavior of the metamaterial structures: surrounding air, number of unit cells, geometric properties of connected structures. • We describe how the design of the interfaces and the aforementioned factors can be used to optimize the vibration damping performance of the metamaterial in the composed structure.