MICROSCOPIC EXAMINATION OF THE MICROSTRUCTURE AND DEFORMATION OF CONVENTIONAL AND AUXETIC FOAMS

Auxetic materials have a negative Poisson's ratio, that is, they expan d laterally when stretched longitudinally. One way of obtaining a nega tive Poisson's ratio is by using a re-entrant cell structure. Auxetic foam was fabricated from a conventional polymeric foam. Assuming simil ar mechanical properties for the solid material comprising the foams, the principle variable affecting the properties of the foam is the geo metry of the cells. This means that the unusual mechanical properties of auxetic foams are attributed to the deformation characteristics of re-entrant microstructures. In this paper, the results of optical- and scanning electron-microscopic studies of the geometrical parameters f or the different foams examined are presented. Examples of the microst ructural deformation mechanisms observed are also presented. Compariso n between the conventional foams and their auxetic conversions are als o made.