University of Manchester

In situ deformation of auxetic polymeric foam

Sam McDonald
Project Completed

Scientific Case


Experiment Design

Deformation of cell joints and struts

Cell walls: 100 micron
Resolution: 10 micron
Scanners and Rigs
Nikon Custom 320kV Bay

Sample & Safety

Low Hazard

Scan Records

Nikon Custom 320kV Bay
Scan dates: 2010-07-01 to 2010-07-01 for 10 scans.

Project Report

X-ray microtomography has been used to study in situ the uniaxial tensile response of low-density polyurethane foam. Two variants have been examined, one before and one after treatment to generate auxetic behaviour. For both variants, microstructurally faithful finite element (FE) models have been constructed from the initial tomographs. For each variant a series of tomographs have been collected during progressive straining. Poisson’s ratios of 0.30 (conventional, non-auxetic) and _0.22 (auxetic) have been measured for the two variants by digital image correlation (DIC) between successive images. By comparison, the FE models exhibited Poisson’s ratio’s of 0.5 and _0.3, respectively. Key micromechanical mechanisms responsible for the auxetic effect have been observed during straining, such as the straightening of bent ribs and rotation of nodes (joints), compared to changes in the angles between essentially straight struts for the non-auxetic variant. The microstructurally faithful FE models confirm the mechanisms observed in the experiments and enabl

S.A. McDonald, G. Dedreuil-Monet, Y. Tao Yao, A. Alderson and P.J. Withers, In situ 3D X-ray microtomography study comparing auxetic and non-auxetic polymeric foams under tension, Phys. Status Solidi B 248, 45 (2011).