Functionally Graded and Geometrically Modified Auxetic Re-Entrant Honeycombs: Experimental and Numerical Analysis

Area of Science:

• Materials Science
• Mechanical Engineering
• Additive Manufacturing

Background:

• Auxetic re-entrant (RE) honeycombs exhibit a negative Poisson's ratio (NPR), offering enhanced energy absorption compared to conventional hexagonal honeycombs.
• Design modifications are key to further improving the energy absorption capabilities of these auxetic structures.

Purpose of the Study:

• To explore novel double-cylindrical-shell-based RE unit cell (REC) designs with negative Poisson's ratios (NPRs).
• To analyze the impact of material variations on the NPR of these novel REC designs.
• To investigate two distinct geometric configurations: narrow REC (REC-N) and wide REC (REC-W).

Main Methods:

• Samples of novel REC geometries were fabricated using additive manufacturing (AM).
• Materials used included polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and functionally graded (FG) PLA-ABS composites.
• Compression tests were performed according to ASTM-D695-15 standards to determine Poisson's ratios, with results validated against numerical simulations.

Main Results:

• The study demonstrated that NPR can vary by up to 20% by altering the REC cell geometry for a given material.
• Changes in material composition were shown to alter the NPR by up to 11%.
• Both REC cell design and material variations significantly influence the resulting NPR.

Conclusions:

• Novel double-cylindrical-shell RECs exhibit tunable negative Poisson's ratio behavior.
• The findings highlight the significant impact of both geometric design and material selection on the auxetic properties of RECs.
• This research provides a foundation for optimizing auxetic materials for specific energy absorption applications.