Re-Entrant Honeycomb Auxetic Structure with Enhanced Directional Properties

Area of Science:

• Materials Science
• Mechanical Engineering
• Solid Mechanics

Background:

• Auxetic materials exhibit a negative Poisson's ratio (NPR), expanding laterally when stretched.
• Re-entrant honeycomb structures are a class of auxetic materials with unique deformation characteristics.
• Existing designs may have limitations in achieving high NPR or specific directional properties.

Purpose of the Study:

• To present a modified re-entrant honeycomb auxetic structure with increased compliance.
• To enhance the negative Poisson's ratio (NPR) of auxetic structures.
• To investigate the effect of structural modifications on directional mechanical properties.

Main Methods:

• Development of an analytical model considering bending, shear, and axial deformations.
• Validation of the analytical model using finite element analysis (FEA).
• Experimental verification through tensile testing.

Main Results:

• The modified structure achieves significantly enhanced NPR in the x-direction under loading.
• The addition of a horizontal member influences directional properties, reducing NPR in the y-direction.
• The structure demonstrates an improved Young's modulus compared to solid materials, especially at low strut-to-re-entrant length ratios.
• High NPR is achievable at low relative densities compared to semi re-entrant honeycomb structures.

Conclusions:

• The modified re-entrant honeycomb auxetic structure effectively increases compliance and enhances NPR.
• Structural modifications offer tunable directional mechanical responses.
• The proposed design provides a pathway to achieving high NPR with low relative density.