Design and Implementation of Mechanical Metamaterials
Essink, Brittany
2020
Abstract
The use of mechanical metamaterials, or metastructures, for vibration suppression has recently emerged as a viable approach to creating vibrationally resilient systems. Previous designs have proven to be effective at attenuating vibrations, however additional concerns arise with the use of these devices. Although many metastructures predict an improved performance, many have not been experimentally validated due to the infeasibility of creating their complex geometries before the advent of additive manufacturing. Additionally, the existing research has only considered designs excited in one or two directions. This research successfully designs and fabricates the first multi axis mechanical metamaterial capable of attenuating vibration under excitation in the longitudinal, transverse, and torsional directions. This multi axis metastructure is experimentally validated against FEM and analytical models. The majority of these metastructure devices are additively manufactured from polymers having a high amount of inherent material damping. Metastructure systems are often created for a specific use case and the geometries are optimized with a chosen material without considering the tradeoffs between optimizing the design and the effect of material damping. This work analyzes cases and frequency ranges of interest where using a highly damped material will outperform an optimized geometry and is the first to determine a dividing line between material damping and vibration absorption in mechanical metamaterial design. Considering both two degree of freedom and multi axis degree of freedom excitation structures, frequency responses suggest that for a system where a specific excitation frequency is to be avoided, it is more beneficial from a displacement reduction standpoint to tune absorbers to this frequency instead of adding system damping. Alternatively, if the system excitation is varying or broadband, increased damping provides a lower global displacement over a broader frequency range suggesting that for this excitation scenario, increasing material damping outperforms absorber tuning. By using the criteria provided in this thesis, a decision can be made on the most effective system design given known excitation constraints. These criteria can help determine whether it is necessary to undergo costly geometric optimization processes. The peak separation capabilities of the multi axis mechanical metamaterial are considered for augmentation through a control system located on the distributed absorber system. An electromechanical model of including a piezoelectric bimorph to sense and actuate the absorber system is derived. A pole placement control system is introduced to adjust the natural frequencies of the absorbers. While a control system is not recommended to be used in this design case due to the high stresses in the piezoelectric material during excitation, a base method for active control of the absorbers of a metastructure with regards to peak separation is created. Additional insight on control use in mechanical metamaterials is discussed, including recommendations on when an active control system should be considered.Subjects
Mechanical metamaterials Metastructures
Types
Thesis
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