Amajor challenge that civil structures are required to withstand, lies in the form dynamic loading, the most demanding being seismic excitation. Novel types of configurations have been recently introduced for structural applications in the form of metamaterials. In order to maximize the potential that such configurations can offer, nonlinear behaviour is explored. An attempt to scale up their beneficial properties, leads to the investigation of impact phenomena within the unit cell scale. The proposed design consists of multiple, periodically arranged unit cells, as shown in Figure 1. Each cell is composed of an outer container and an inner mass, which is free to impact on the sides. The configuration is inserted between a protected structure and its support and the purpose of its implementation is to absorb energy from the primary system.
Figure 1: Nonlinear metamaterial lattice.The effectiveness of the system in vibration attenuation is measured in terms of the energy, which is absorbed from the system due to impacts. In Figure 2, the percentage of the absorbed energy with respect to the total inserted energy is plotted for varying parameters of the system, while the lattice consists of 2 cells. It can be observed that the energy absorption performance of the configuration is significant, especially for increasing mass of the unit cells.
Figure 2: Energy absorption for 2 unit cells at resonance.An important aspect is the implementation of metamaterial solutions for the protection of structures on site. An effective application, that can also be implemented for existing structures, is that of the meta-barrier, where the metamaterial configuration protects a specific region of soil, within which the structure is founded, as shown in Figure 3. Installation of the proposed metamaterial will target surface waves and leads to energy absorption and prevention of wave propagation within specific frequencies.
Figure 3: Coupling of metamaterial configuration with the protected structure.
Μore information is openly available in a recent publication (Chondrogiannis et al., 2020): https://doi.org/10.47964/1120.9338.19599. The above video contains the associated conference presentation in the XI International Conference on Structural Dynamics.