Density change during the manufacturing process of PU–PE open cell auxetic foams

Abstract

This paper describes a modified manufacturing route involving a large change in density in auxetic negative Poisson's ratio (NPR) foams. Density change of auxetic foams after manufacturing is a common feature for this porous material. Samples of open cell PU-PE (i.e. the combination of polyurethane-polyethylene) foams with NPR are produced from two similar native materials using both the classical and the novel custom manufacturing methods. In the classical manufacturing route the cooling process is typically carried out with the foam in a confined state. Conversely, in the new manufacturing process it was substituted with a release process. Samples were subjected to both tensile and compressive loading, as well as density measurements. A thorough mechanical characterisation of the foams is described, linking the mechanical properties with their change in density after conversion into auxetic.

A review of the manufacture, mechanical properties and potential applications of auxetic foams

“…Bianchi et al have also recently presented a more classical example of auxetic fabrication resulting in large changes of the density of the auxetic foams. Manufacturing saw two batches of foam samples of varying dimensions placed into a metallic tube mould and compressed.…”

“…Numerous temperature–time combinations have been reported in the literature and are summarised in Fig. , where the heating time varied from 6 to 60 min but the majority of the time–temperature combinations were less than 20 min. The temperature applied varied between 130 and 220 °C , this wide range of temperatures can be explained considering the findings of Wang et al that foams with smaller cell size need higher heating temperatures and shorter processing times compared to foams with larger pore size.…”

Partially auxetic behavior in fcc crystals of hard-core repulsive Yukawa particles

“…Depending on whether negative values of Poisson ratio are observed in all crystallographic directions, in some of them or in none of them, one can define all materials as auxetics, partial auxetics and nonauxetics, respectively (). Recently, increasing interest in studies of auxetic materials and models was observed .…”

Deformation analysis of reinforced‐core auxetic assemblies by close‐range photogrammetry

“…Despite the variety of auxetic systems presented in the literature, manufacture of auxetic materials still remains a challenge. Several manufacturing routes have been proposed to convert a conventional (positive Poisson's ratio) foam into the auxetic one using heat treatment, thermo‐forming and compaction . The main approaches used for experimental manufacturing of auxetics are based on the rapid prototyping techniques such as the soft lithography , the selective electron beam melting , the digital micromirror device projection printing and the dip‐in direct laser writing .…”