Necking in Silica Filled Poly(dimethyl siloxane) and the Resulting Mechanical Properties of the Necked Material

Necking in uniaxial tension experiments has been well studied in filled and unfilled semi-crystalline polymers and plastics below their glass transition temperature (Tg), although necking has not been observed for filled or unfilled elastomers above Tg. We report for the first time, the necking behavior of cross-linked (1phr Dicumyl peroxide), poly (dimethylsiloxane) rubber filled with 30phr or more of high surface area (>300m2/g) fumed silica. The linear and non-linear mechanical properties of the neck material have been studied via the (i) dynamic shear analysis including the Payne effect, (ii) uniaxial tension tests including Mullins effect (iii) the tensile strength and (iv) tear resistance as measured by the trouser test. The results for the neck material were compared to the results of the same experiments for the silica-filled PDMS rubber systems where the filler content, surface area and surface treatment were such that necking was not observed. The tensile strength and tear resistance of the necked material was found to be on the average 50-100% higher than the corresponding values for non-neck forming systems. A potential mechanism for the observed necking behavior will be discussed.