Tomographic examination of auxetic polyurethane foam structures (Phys. Status Solidi B 2/2014)

Abstract

The back‐cover article by Lisiecki et al. (pp. http://doi.wiley.com/10.1002/pssb.201384242) presents various tests carried out on auxetic foams developed in the Air Force Institute of Technology (Warsaw, Poland) according to a novel Mechanical‐Chemical‐Thermal process. The tests were aimed at estimating the difference in structure as well as mechanical properties of the manufactured foam specimens throughout their volume. Therefore the processed foams were divided into subspecimens and tested separately. Within the article a detailed insight into the structure of conventional as well as auxetic foams is presented and the most important differences are highlighted. The thesis of the article is that the difference in mechanical properties is highly dependent on the volumetric compression ratio which is the characteristic parameter of the manufacturing process. Obtained results will help to adjust the M‐Ch‐T process in order to achieve more uniform foams or foams with tailored properties. Financially supported by Structural Funds in the Operational Programme – Innovative Economy (IE OP) financed from the European Regional Development Fund – Project “Modern material technologies in aerospace industry”, Nr. POIG.01.01.02‐00‐015/08‐00.

Quasi-static characterisation and impact testing of auxetic foam for sports safety applications

“…The inhomogeneity arises due to issues of achieving uniform compression and temperature fields throughout the sample during conversion, and these are especially apparent as the sample size increases [8,9,18]. The inner regions of the cubes reported in this work were less compressed (lower VCR - Figure 5a) and had lower initial stiffness (Figure 3b), in agreement with previous work utilising a mechanical-chemical-thermal process [19]. The stress-strain curve for samples taken from the centre of a cube had a slight plateau region (Figure 3a), characteristic of a low level of compression during conversion [16] and consistent with less modification of the foam structure after conversion (Figure 4b).…”

“…14] (smallest dimension < 25 mm), while more recent work has produced larger samples [e.g. [15][16][17][18][19]] (50 mm < smallest dimension < 100 mm) as the research has moved towards applications. Poisson's ratios are typically calculated from true strain measurements, obtained by filming and tracking the location of marks applied to a sample subject to quasi-static tension or compression.…”

“…Previous work has shown inhomogeneity in the structure of converted foam [19]. Cellular structure (geometry and orientation) contributes significantly to the mechanical properties of a cellular solid [7,21,22].…”

Finite deformation and fractional order viscoelasticity of an auxetic foam

“…The experimental behavior of various auxetic foam materials has been extensively studied. The compressive stress/strain behavior has been studied by Bezazi and Scarpa (2007), Pastorino et al (2007), Lisiecki et al (2014), Duncan et al (2021), and the cyclic compressive stress/strain behavior by Casavola et al (2021), Bezazi and Scarpa (2007), Zhang et al (2020), Duncan et al (2016), Opreni et al (2020). Due to their negative Poisson's ratio behavior, it is important to examine the Poisson behavior of auxetic foams as strain changes.…”