The Mechanical Properties of Conventional and Auxetic Foams. Part I: Compression and Tension

Abstract

Auxetic foams exhibit the unusual property of a negative Poisson's ratio and hence expand laterally when stretched. In this, the first of two papers, a systematic study is made of the mechanical properties of a range of foams fabricated to have different negative Poisson's ratios. The stress-strain behaviour, in both tension and compression, is compared with conventional foams. Values for the Young's moduli and Poisson's ratios in the three principal directions, in both tension and compression, are obtained. Negative Poisson's ratios ranging between -0.2 and -0.9 in tension, and between -0.1 and -0.8 in compression have been obtained. The effect of densification, during loading is significantly enhanced in auxetic foams, and this significantly affects the stress-strain curves. The creep resistance of the foams is also examined.

A novel mechanism for generating auxetic behaviour in reticulated foams: missing rib foam model

“…the auxetic specimen, which is typical of this particular foam material [3,18]. Both the hexagonal and missing rib models predict a higher value of E for the conventional foam than the auxetic.…”

Auxetic Foam for Snow-Sport Safety Devices

“…Chan and Evans [34] reported slightly lower Poisson's ratios for auxetic foam under tension in comparison to compression. In this work, Poisson's ratio was measured in tension to avoid issues with, (1) contact surface friction when compression testing thin sheets [24][25][26] and, (2) positioning and tracking pins in a small sample (cut from the sheet) under compression.…”

“…The conversion process can be applied to a range of materials [e.g. 34,38], and highly anisotropic auxetic foam can be obtained by applying different amounts of compression in each direction during fabrication [39]. When applying the thermo-mechanical process, there is, as yet, no consensus regarding the best heating time and temperature combination to maximise auxetic behaviour.…”

“…Poisson's ratio is often measured during low-speed stretching or compression, by tracking the position of markers on a sample followed by linear regression of lateralstrain vs. axial-strain data in the low axial-strain region [e.g. 25,34]. Negative Poisson's ratios have been measured for auxetic foams subject to high-speed compression [24,43].…”

“…Their stressstrain curves have an extended quasi-linear region and the foam densifies earlier as a result of lateral contraction [34]. This lateral contraction can cause auxetic foam to deform less in the direction of the applied load under impact [23] and reduce peak force in comparison to conventional open-cell foam [23,24].…”