Active Metastructures for Light-Weight Vibration Suppression

Abstract

The primary objective of this work is to examine the effectiveness of metastructures for vibration suppression from a weight standpoint. Metastructures, a metamaterial inspired concept, are structures with distributed vibration absorbers. In automotive and aerospace industries, it is critical to have low levels of vibrations while also using lightweight materials. Previous work has shown that metastructures are effective at mitigating vibrations but does not consider the effects of mass.

This work considers mass by comparing a metastructure to a baseline structure of equal mass with no absorbers. The metastructures are characterized by the number of vibration absorbers, the mass ratio, and the natural frequencies of the vibration absorbers. The metastructure and baseline structure are modeled using a lumped mass model and a distributed mass model. The lumped mass model allows for mass and stiffness parameters to be varied independently without the need to consider geometry constraints. The distributed mass model is a more realistic representation of a physical structure and uses relevant material properties. The steady-state and transient time responses of the structure are obtained. The results of these models examine how the performance of the structure varies with respect to the number of vibration absorbers and the mass ratio. Additionally, the stiffness and mass distributions of the vibration absorbers are considered. When the ratio of stiffness over mass varies linearly, the absorbers create broad-band suppression. Overall, these results show it is possible to obtain a favorable vibration response without adding additional mass to the structure.

The distributed vibration absorbers are realized through geometry modifications on the centimeter scale. To obtain the complex geometry needed for these structures, the metastructures are typically manufactured using 3D printers, specifically the Objet Connex 3D printer. To better understand the damping properties of the materials used by the Objet Connex, the viscoelastic properties are characterized. These properties are characterized by measuring the frequency and temperature dependent complex modulus values using a dynamic mechanical analysis (DMA) machine. The material properties are incorporated into the Golla-Hughes-McTavish (GHM) model to capture the damping effect. Using the time-temperature equivalence, the material properties are transformed to various temperatures, allowing the response of the structures to be modeled at various temperatures. A 3D printed metastructure is experimentally tested and compared to the GHM model. These results show the GHM model can accurately predict the natural frequencies of the vibration absorbers.

Lastly, the concept of adding active vibration control to a metastructure to get additional vibration suppression is explored. This is done by attaching piezoelectric materials to the metastructure and utilizing the positive position feedback (PPF) control law to further reduce vibrations. Two active vibration absorber designs are explored; the first uses a stack actuator to control the position of a single absorber and the second design bonds PZT patches in a bimorph cantilevered configuration to the beam of one absorber. This work shows that the active vibration absorber design utilizing a stack actuator is not practical, but the PZT bimorph configuration is capable of further reducing vibrations. Due to the metastructure design, each mode corresponds to the oscillation of a single absorber. When a single vibration absorber is active, the controller can control the corresponding mode. Overall, this shows that integrating active vibration control into a metastructure design can provide additional performance improvements.