High stiffness - high damping chiral metamaterial assemblies for low-frequency applications

Stiffness and damping are conflicting requirements in many material systems. High stiffness is required in a wide range of structural components to provide sufficient robustness under demanding loading conditions. Simultaneously, a structure should be able to effectively mitigate shock and vibrations dynamically transmitted to it by the environment. While most conventional structures currently exhibit limited adaptability and damping capabilities, design strategies to simultaneously endow structural assemblies with high stiffness and high damping performance are proposed in this work. To this aim, a backbone structure suitable to meet stiffness requirements is combined with metamaterial inclusions able to provide fully-passive shock and vibration absorption. Viscoelastic resonant lattices with chiral topology are employed as inclusions, whose aim is to confine vibrational energy,pump it a way from the backbone structure,and dissipate it through viscoelastic damping. The lattices are composed by an elastomeric matrix with the desired chiral shape, and stiff resonating inclusions are inserted at nodal locations. Both finite element simulations and experimental tests demonstrate that periodic chiral assemblies give rise to wide frequency bandgaps. Low-frequency tuning of the assembly for effective suppression of the first resonant mode of a backbone structure represented by an aluminum box-beam is demonstrated both numerically and experimentally. The considered lightweight inclusion is a chiral matrix realized with castable rubber,featuring graded cylinder mass insertions. The proposed design methodology can be flexibly tailored to various frequency ranges and is applicable to both existing and novel structural components at different scales.