Session: 16-01-01: NSF-funded Research (Grad & Undergrad)

Paper Number: 77032

Start Time: Wednesday, 02:25 PM

77032 - Magneto-Mechanical Metamaterials With Widely Tunable Mechanical Properties 

Metamaterials are fabricated materials, which through their geometry or assembled order of repeated unit cells throughout their structure, can exhibit properties and responses to external stimuli or loading that are not typical of naturally occurring materials. Previous metamaterial designs are mostly static structures which cannot be modified following their initial fabrication, resulting in pre-determined unchangeable mechanical properties. In this work, we report a magneto-mechanical soft metamaterial, whose structural configuration can be remotely influenced with magnetic fields, allowing for tunable mechanical properties of the metamaterial after initial fabrication. Large extent of potential deformation via applied magnetic fields was made possible with the inclusion of hard-magnetic particles with permanent magnetization directions embedded in a soft elastomeric matrix material. Incorporation of a unique asymmetric joint design also allows for two distinct modes of actuation, including a bending and folding of the unit cells depending on the orientation of the applied magnetic field with respect to the magnetization distribution in the unit cells.

Finite-element analysis (FEA) with a user-defined element subroutine was utilized to simulate the magnetically actuated mechanical deformation of the metamaterial unit cell and assemblies. Stiffness and Poisson’s ratios of the deformed metamaterial were calculated based on the simulation results to evaluate the tunability of the unit cell and array properties. Both pure magnetic actuation and combined loading scenarios, the latter consisting of additional mechanical compression beyond the initial pure magnetic actuation of the structure, were simulated to investigate the wide range of deformation and corresponding properties. The two distinct loading steps, magnetic actuation and additional uniaxial mechanical compression, also involved two separate symmetries of the unit cells, with the former possessing a four-fold symmetry and the latter with a decreased two-fold symmetry. The FEA simulation on the deformation and properties were then compared with the experimental results of fabricated samples, showing successful prediction of the two distinct deformation modes of the unit cells and arrays observed during the experimental application of magnetic fields and additional mechanical loading. A tunable stiffness of the structures and wide range of Poisson’s ratios – including a negative Poisson’s ratio of the structure under certain conditions – were achievable based on the magnitude and direction of the applied magnetic field, as well as the extent of subsequent mechanical compression applied to the metamaterial beyond pure magnetic actuation.

We anticipate this magneto-mechanical metamaterial with multiple actuation modes and range of achievable tunable properties to enable a wide variety of applications, including structures and material architectures requiring shape reconfigurations under remote actuation, wide ranges of

stiffnesses depending on expected loading and use, and reconfigurable electromagnetic metamaterial devices such as reconfigurable antennas, filters, or frequency selective surfaces that provide multi-functional performance for radio-frequency applications.

Presenting Author: Cole Zemelka Ohio State University

Authors:

Cole Zemelka Ohio State University
Shuai Wu Stanford University
Ruike Zhao Stanford University