Triclinic Metamaterials by Tristable Origami with Reprogrammable Frustration.

Area of Science:

• Materials Science
• Mechanical Engineering
• Origami Engineering

Background:

• Metamaterials achieve unique properties through geometrical-frustration-induced anisotropy and inhomogeneity.
• Neumann's principle states that less symmetry in a unit cell leads to anisotropic responses.
• Conventional materials lack the tunable anisotropy achievable with designed unit cells.

Purpose of the Study:

• To present a triclinic metamaterial system of minimal symmetry using a Trimorph origami pattern.
• To explore the geometrical-frustration-induced anisotropy and inhomogeneity in this system.
• To investigate the unusual Poisson effect and programmable states arising from the origami geometry.

Main Methods:

• Design of a unit cell based on a Trimorph origami pattern with four tilted panels and creases.
• Theoretical prediction and experimental observation of the folding motion, strain coupling, and Poisson effect.
• Analysis of nonlinear folding dynamics leading to tristable states and defect emergence upon tessellation.

Main Results:

• A triclinic metamaterial with minimal symmetry was successfully designed and fabricated.
• An unusual, reversible auxetic Poisson effect was observed due to changing primitive vectors and coupled strains.
• Geometric frustration led to emergent phenomena resembling linear and point defects, enabling reprogrammable inhomogeneous states.

Conclusions:

• The Trimorph origami enables the creation of novel origami metamaterials with tunable anisotropy.
• The system exhibits unique properties like reversible auxeticity and emergent defects.
• Potential applications include wave propagation control and compliant microrobots.