Bio-inspired hierarchical dissipative metamaterials

TL;DR

This paper investigates how bio-inspired hierarchical structures and viscoelasticity influence wave attenuation in mechanical metamaterials, revealing new band gap features and weight reduction potential for practical structural design.

Contribution

It introduces a method to incorporate hierarchical organization into metamaterials, enhancing wave damping and tunability, with consideration of viscoelastic effects often neglected.

Findings

Hierarchical structures preserve and induce band gaps.

Hierarchies enable lower frequency band gap tuning.

Viscoelasticity significantly affects wave attenuation.

Abstract

Hierarchical structures with constituents over multiple length scales are found in various natural materials like bones, shells, spider silk and others, all of which display enhanced quasi-static mechanical properties, such as high specific strength, stiffness and toughness. At the same time, the role of hierarchy on the dynamic behaviour of metamaterials remains largely unexplored. This study assesses the effect of bio-inspired hierarchical organization as well as of viscoelasticity on the wave attenuation properties of continuous mechanical metamaterials. We consider single-phase metamaterials formed by self-similar unit cells with different hierarchical levels and types of hierarchy. Results highlight a number of advantages through the introduction of structural hierarchy. Band gaps relative to the corresponding non-hierarchical structures are mostly preserved, while additional "hierarchically-induced" band gaps appear. Additionally, the hierarchical configuration allows the tuning of the band gap frequencies of regular metamaterial to lower frequencies, with a simultaneous significant reduction of the global structural weight. We show that even small viscoelastic effects, not treated in the current literature, are essential in determining this behaviour. The approach we propose allows the addition of hierarchical elements to existing metamaterial configurations, with the corresponding improvement of the wave damping properties, thus providing indications for the design of structures for practical applications.