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Characterization, stability, and application of domain walls in flexible mechanical metamaterials
Edited by Itai Cohen, Cornell University, Ithaca, NY, and accepted by Editorial Board Member John A. Rogers October 12, 2020 (received for review July 27, 2020)

Significance
Mechanical metamaterials are an interesting platform to reproduce atomistic-scale phenomena at the macroscale and to exploit them to achieve additional functionalities. An interesting feature of many ordered solid-state materials is the formation of domain walls that separate different phases. While these interfaces have been reproduced in a variety of mechanical materials, the understanding of how to control them is still poor owing to their structural complexity. Here, we use a combination of experimental, numerical, and theoretical tools to engineer the domain walls emerging upon uniaxial compression in a mechanical metamaterial based on the rotating-squares mechanism. Our study reveals additional territories in the mechanical metamaterials design space which could unlock more tools for information encryption, stiffness tuning, and wave guiding.
Abstract
Domain walls, commonly occurring at the interface of different phases in solid-state materials, have recently been harnessed at the structural scale to enable additional modes of functionality. Here, we combine experimental, numerical, and theoretical tools to investigate the domain walls emerging upon uniaxial compression in a mechanical metamaterial based on the rotating-squares mechanism. We first show that these interfaces can be generated and controlled by carefully arranging a few phase-inducing defects. We establish an analytical model to capture the evolution of the domain walls as a function of the applied deformation. We then employ this model as a guideline to realize interfaces of complex shape. Finally, we show that the engineered domain walls modify the global response of the metamaterial and can be effectively exploited to tune its stiffness as well as to guide the propagation of elastic waves.
Footnotes
↵1B.D. and S.Y. contributed equally to this work.
- ↵2To whom correspondence may be addressed. Email: bertoldi{at}seas.harvard.edu.
Author contributions: B.D., S.Y., V.T., and K.B. designed research; B.D., S.Y., and A.E.F. performed research; B.D., S.Y., V.T., and K.B. analyzed data; and B.D., S.Y., A.E.F., and K.B. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission. I.C. is a guest editor invited by the Editorial Board.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2015847117/-/DCSupplemental.
Data Availability.
All study data are included in this article and SI Appendix.
Published under the PNAS license.
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