Handedness in shearing auxetics creates rigid and compliant structures

Area of Science:

• Materials Science
• Mechanics
• Geometry

Background:

• Nature utilizes repeating units to create complex, handed structures with tunable mechanical properties.
• Auxetic materials, characterized by negative Poisson's ratio, expand under tension and are built from repeating unit cells.
• Achieving handedness in auxetic structures has been a challenge, limiting their design complexity and applications.

Purpose of the Study:

• To develop a method for introducing handedness into auxetic unit cells that exhibit shear deformation during expansion.
• To explore the design rules governing the symmetry and alignment of auxetic tilings for controlled handedness.
• To demonstrate the fabrication of handed shearing auxetics capable of tiling various surfaces and forming composite structures.

Main Methods:

• Investigated symmetry and alignment principles in auxetic tilings to induce handedness.
• Developed rules for creating handed auxetic unit cells that shear upon tension.
• Applied these rules to design auxetics that tile planar, cylindrical, and spherical geometries.
• Composited handed shearing auxetics, mimicking natural materials like keratin and collagen.

Main Results:

• Successfully produced auxetic unit cells with controllable handedness and shear behavior.
• Demonstrated the ability of these handed auxetics to tile complex surfaces (planes, cylinders, spheres).
• Created composite structures exhibiting tunable properties, from compliant twisting materials to rigid locking deployable systems.

Conclusions:

• The developed symmetry and alignment rules enable the creation of novel handed shearing auxetic materials.
• These materials offer unprecedented control over mechanical responses, including compliance and rigidity.
• The findings open new avenues for designing advanced materials for applications in chemical frameworks, medical devices, robotics, and deployable structures.