Effect of steam conversion on the cellular structure, Young's modulus and negative Poisson's ratio of closed-cell foam

DUNCAN, Oliver, ALLEN, Tom, BIRCH, Alana, FOSTER, Leon, HART, John and ALDERSON, Andrew (2020). Effect of steam conversion on the cellular structure, Young's modulus and negative Poisson's ratio of closed-cell foam. Smart Materials and Structures, 30 (1), 015031.

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Abstract

Open-cell auxetic foams have shown potential for use in sporting and other protective equipment. Previous conversion methods for auxetic closed-cell foam used a bespoke pressure vessel. This work expands upon a recent method, using steam absorption followed by cooling and condensation, to change the cell shape of closed-cell foam to impart a negative Poisson's ratio. Aiming to present a simple, repeatable conversion method, foam samples (20 × 10 × 100 mm) floating in water-filled (~20 °C), covered ceramic containers (300 × 200 × 100 mm) were heated in an oven at 105 °C for between 1 and 6.5 hrs. Based on the results for these smaller samples, a larger sample of foam (30 × 100 × 100 mm) was also converted, with a steaming time of 8 hrs. The final volume ratio (original/final volume) increased with heating time, up to a maximum of 4.6. The amount and angle of re-entrant (inward-folding) cell walls increased with the final volume ratio as cells contracted further, as evidenced by micro-computed tomography. Poisson's ratios, measured using digital image correlation, were as low as −0.3 in tension and −1.1 in compression. The tensile Young's modulus increased from ~2 up to ~6 MPa with the final volume ratio and the compressive Young's modulus reduced from ~1.5 MPa for low values of the final volume ratio between one and three and then remained close to 1.5 MPa.

Item Type:	Article
Uncontrolled Keywords:	auxetic closed cell foam; steam processing; digital image correlation; micro-computed tomography; Poisson’ s ratio; Young’ s modulus; 03 Chemical Sciences; 09 Engineering; Materials
Identification Number:	https://doi.org/10.1088/1361-665X/abc300
Page Range:	015031
SWORD Depositor:	Symplectic Elements
Depositing User:	Symplectic Elements
Date Deposited:	06 Jan 2021 10:28
Last Modified:	09 Dec 2021 01:18
URI:	https://shura.shu.ac.uk/id/eprint/27916

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