Characterization of Auxetic Metamaterials: Experimental and Finite Element Study of Re-Entrant Bowtie and Conventional Honeycomb Structures Fabricated by FDM Using PLA, PETG, and TPU

Characterization of Auxetic Metamaterials: Experimental and Finite Element Study of Re-Entrant Bowtie and Conventional Honeycomb Structures Fabricated by FDM Using PLA, PETG, and TPU

Auxetic metamaterials exhibit a negative Poisson’s ratio (NPR), expanding
transversely under tension and contracting under compression — a response governed
entirely by internal geometry rather than material chemistry. This study presents experimental
and finite element analysis (FEA) of two distinct cellular geometries: a re-entrant bowtie
auxetic lattice and a conventional hexagonal honeycomb, fabricated by fused deposition
modelling (FDM) in three polymers — polylactic acid (PLA), polyethylene terephthalate
glycol (PETG), and thermoplastic polyurethane (TPU) — producing six test configurations.
The tests were done for quasi-static compressions of the material on the 400 kN UTM at an
NABL approved laboratory. The TPU materials had very different behaviour as compared to
the other materials where they deformed outwardly but still continued carrying the load. As
they did not fail during compression, we also tested them through tensile test as well. The
simulations of the structures were done in ANSYS 2026 R1 using static structural analysis
where large deflection effects were considered. However, the PETG bow tie was the
strongest, achieving maximum force of 2240 N and being very close to the simulation result
(only 0.54% deviation). The case of PLA was the opposite; the sample failed quickly and

catastrophically at 1660 N, while the linear-elastic simulation hugely overestimated the
sample strength by 400%. This difference between simulations and experimental data reveals
one of the key drawbacks of linear elastic FE analysis of brittle materials. The situation with
the TPU material was even worse – the mesh deformed so much under large strains that it
was impossible to complete the calculation.

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