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Phase transition and domain wall control in multistable metamaterials

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Abstract

Ferroics and metal alloys are naturally occurring materials, whose constituent unit cells can co-exist in multiple stable configurations. These different configurations organize into regions (domains) separated by boundaries (domain walls). The stable configurations (phases) are associated with a unique set of properties (e.g., dipole orientation, stiffness), rendering the mesoscale phase distributions a crucial factor in determining macroscale material behavior; hence, the desire to control the distribution. Inspired by non-linear physics and potential applications of these natural materials, this dissertation explores similar physics in materials of an engineered microstructure (metamaterials) featuring purely geometric phases, and develops strategies to control domain walls. The domain management strategies enable control of the phase distribution and thereby the macroscale properties, allowing for a highly tunable post-fabrication performance.

In my primary investigation, I leverage both geometric multistability and kinematic amplification in the metamaterial architecture to enable the effective mass, damping and stiffness to be tuned independently post-fabrication to control wave dispersion. In my second project, I introduce an alternate, less invasive strategy utilizing strain engineering to precisely control the phase distribution. In my third project, I propose a general theory to predict the position and velocity of mobile domain walls (i.e., transition waves) when subjected to a small spatio-temporal modulation. The modulations provide a mechanism to counter domain wall motion spurred by inherent energy minimizing affects (e.g., biased potential, domain wall curvature) which can be leveraged for stabilizing and arbitrarily shaping domain contours. Finally, inspired by the pattern forming dynamics of certain biological and chemical systems, I mimic the effects of the underlying driving and dissipative mechanisms within the context of a customizable mechanical system: an elastic metamaterial incorporating active elements (i.e., electric motors) facilitating non-reciprocal interactions. This construction encodes certain periodic phase distributions to be triggered as an inherent response of the metamaterial to perturbation, which may find utility in morphable surfaces.

In providing several strategies to realize and control the phase distributions within multistable metamaterials, this dissertation promotes their adoption for applications in energy harvesting, mechanical memory devices and deployable structures.

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This item is under embargo until September 29, 2024.