Active Mechanical Metamaterial for Tunable Vibration Isolation

Abstract

Materials and material structures with highly specialised and unique mechanical properties are sought after in order to gain the most performance from a system. Materials generally have fixed mechanical properties and are unable to adapt in the case of new or unforeseen situations. Active mechanical metamaterials are able to alter the fundamental mechanical properties in real-time.

The literature review looks at the state of the art active mechanical metamaterials from the perspective of their control strategies and actuation principles. This is done to get a better view of what materials are out there, what applications are suitable for specific active mechanical metamaterials and what gaps can be explored in the future.

The literature review found that the active mechanical metamaterials can be classified by type of control into closed loop and open loop control, as well as the location of actuation into locally actuated and globally actuated materials. Furthermore, the active mechanical metamaterials are highly specialised for their respective applications.

Controlling the active mechanical metamaterials effectively, especially with a large amount in unit cells is the main challenge for most of the active mechanical metamaterials. For this propose, globally actuated and open loop control principles provide the best opportunities for simple, large scale controllable active mechanical metamaterials, though the actuation domains used for the globally actuated active mechanical metamaterials is less precise than the domains used in the closed loop active mechanical metamaterials.

The main report proposes an approach to place and manipulate the band gaps in local resonance mechanical metamaterials via open loop actuation. The state of the art local resonance mechanical metamaterials are lacking in tunability of the band gaps, even though the ability to change the location of these band gaps is very desirable to alter the dynamics of the system.

The design concept is based on the working principle of a local resonance mechanical metamaterial and incorporates a method for tuning the resonator stiffnesses. The tunable stiffness is achieved through the straining of opposing flexures, which are actuated by externally applying a strain to the unit cell through the use of chevron motion amplifiers.

The fabricated prototype showed comparable stiffnesses to the stiffnesses obtained using the FEM analysis, and showed an increase of the resonator stiffness from 1530 N/m to 3290 N/m. Furthermore, the prototype showed a change in band gap from between 73 Hz and 86 Hz to between 78 Hz and 92 Hz in response to the application of lattice pre-strain of 0.50mm. This mechanical metamaterial is therefore successful in the tuning of antiresonances in local resonance mechanical metamaterials through externally applying a strain to the metamaterial. In the future, mechanical metamaterials with this tunable band gap behaviour can be useful for applications where a lightweight, open loop, tunable vibration isolation approach is required.