Geometric mechanics

Althoumiura_figgh admired for its aesthetic qualities for centuries, the Japanese art of origami is beginning to be seen as a paradigm for designing mechanical meta-materials. The basis for these new research directions come from the constraints that arise when folding a a thin sheet: the coupling between mechanics and geometry in thin elastic structures generates the possibility for new materials and mechanisms simply by folding, since strategically weakening the material allows for deformations that would otherwise be energetically prohibitive.
To understand origami as a material, we have to start by examining a lattice, or tessellation, of folded unit cells. Recent work has shown that folded structures, in addition to displaying exotic mechanical properties such as a negative Poisson’s ratio, also include reversible “pop-through defects”. These defects behave similarly to crystallographic defects in naturally occurring materials, and can be used to program mechanical stiffness and anisotropy into tessellated origami structures.

Lattice mechanics of origami tessellations
A. A. Evans, J. L. Silverberg, and C. D. Santangelo (arxiv preprint)

Origami structures with a critical transition to bistability arising from hidden degrees of freedom
J. L. Silverberg, J.-H. Na, A. A. Evans, B. Liu, T. C. Hull, C. D. Santangelo, R. J. Lang, R. C. Hayward, and I. Cohen
Nat. Mater. 14, 389-393 (2015)

Programming Reversibly Self-Folding Origami with Micro-patterned photo-crosslinkable polymer trilayers
J.-H. Na, A. A. Evans, J. Bae, M. C. Chiapelli, C. D. Santangelo, R. J. Lang, and R. C. Hayward
Adv. Mater. 27: 79-85 (2015)

Using origami design principles to fold reprogrammable mechanical metamaterials
J. L. Silverberg, A. A. Evans, L. McLeod, C. D. Santangelo, R. C. Hayward, T. C. Hull, and I. Cohen
Science345 (6197): 647-650 (2014)

Tunable mechanics in shells

cropped-huffman1.pngCurved shells are inherently stiffer than their flat counterparts, a fact that is used in both engineering and biology to create stable structures.

This coupling between geometry and mechanics can be useful in creating fast-snapping shells, programming shapes with an external stimulus, or in guiding vibrations within the shell itself.

Geometrically controlled snapping transitions in shells with curved creases
N. P. Bende, A. A. Evans, S. Innes-Gold, L. Marin, I. Cohen, R. C. Hayward, and C. D. Santangelo (arxiv preprint)

This work was featured on LiveScience

Photothermally-Reprogrammable Buckling of Nanocomposite Gel Sheets
A. W. Hauser, A. A. Evans, J.-H. Na, and R. C Hayward
Angew. Chem. Int. Ed. 54, 18, 5434-5437 (2015)

Reflection and Refraction of Flexural Waves at Geometric Boundaries
A. A. Evans and A. J. Levine
Phys. Rev. Lett. 111 038101 (2013)

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