Topological characteristics and mechanical properties of uniaxially thermoformed auxetic foam

Zhang, Qicheng, Lu, Wenjiang, Scarpa, Fabrizio, Barton, David, Rankin, Kathryn, Zhu, Yunpeng, Lang, Zi-Qiang and Peng, Hua-Xin (2021) Topological characteristics and mechanical properties of uniaxially thermoformed auxetic foam. Materials & Design, 211, [110139]. (doi:10.1016/j.matdes.2021.110139).

Abstract

We present here a simplified procedure to manufacture auxetic PU foam via a single direction thermoforming compression process applied to conventional (pristine) open cell foam samples. The auxetic foams produced here have a Poisson's ratio ν ₂₁ ranging from −1 to 0 in the 1–2 plane and a tangent modulus E _t2 ranging from 0.2 MPa to 2 MPa. X-ray μ-CT and 3D skeletonization enabled the extraction of the topological parameters of the pristine and the auxetic foams. The auxetic foam is transverse isotropic with cell structures exhibiting a re-entrant shape along the thermoforming compression direction 1. More ribs are also oriented within the transverse plane 2–3, in which the stiffness is larger. Tensile and compression quasi-static tests have been carried out on samples cut along different directions and having various thermoforming compression ratios r _c. Auxeticity is present in the in 1–2 plane only for compression ratios between 40% and 80%. Finite Element models for the pristine and auxetic foams have also been built from the μ-CT scanned 3D models. The numerical results show a good agreement with the experimental data and help explaining the deformation mechanisms of these auxetic foams.

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Contributors

Author: Kathryn Rankin

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