Impact properties of uniaxially thermoformed auxetic foams

Qicheng Zhang, Fabrizio Scarpa*, David A W Barton, Yunpeng Zhu, Ziqiang Lang, Dayi Zhang, Hua-xin Peng

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

19 Citations (Scopus)
95 Downloads (Pure)


This work describes large strain quasi-static and impact tests of a new class of low-cost, uniaxially thermoformed, transverse isotropic auxetic foams with compression ratio ranging from 20% to 80%. A custom drop tower rig with high-speed cameras suitable for these soft porous foam materials is designed and used to perform impact tests with energy ranging from 0.38J to 1.90J, corresponding to strain rates from 64/s to 143/s. The thermoformed foams only show auxeticity when loaded along the transverse direction to the uniaxial thermoforming compression, with Poisson’s ratio ν_21 reaching as low as -1.5 at 20% strain and then close to 0 at large strains. The samples deform with large shear band deformations, also due to the auxeticity. The negative Poisson’s ratio foams along that transverse direction also show enhanced impact energy absorption performance, with normalized peak force reduction as high as ~40% against the pristine foam; the reduction is however 20% along the thermoforming direction. A constitutive model based on Nagy’s approach is applied to describe the enhancement of dynamic stress during the impact tests compared with the quasi-static one, due to strain rate effects.
Original languageEnglish
Article number104176
Number of pages17
JournalInternational Journal of Impact Engineering
Early online date20 Jan 2022
Publication statusPublished - 1 May 2022

Bibliographical note

Funding Information:
This project has been supported by the UK Engineering and Physical Sciences Research Council (EPSRC) EP/R032793/1 SYSDYMATS. FS and HXP acknowledge the support of the University of Bristol and Zhejiang University through the InCIS-ACCIS PhD Collaboration program and ZJU's Overseas Academician Joint Lab for Advanced Composite Materials and Structures. FS also acknowledges the support of the ERC-2020-AdG 101020715 NEUROMETA project.

Publisher Copyright:
© 2022 Elsevier Ltd

Structured keywords

  • Engineering Mathematics Research Group


  • Auxetic foam
  • Negative poisson’s ratio
  • Uniaxially thermoform
  • Impact
  • Drop tower
  • Energy absorption


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