Necking in fumed silica filled poly(dimethylsiloxane) and the resulting mechanical properties of the necked material

Necking is a well known phenomenon in uniaxial extension of filled and unfilled semi-crystalline polymers as well as amorphous polymers below their glass transition temperature; however, necking has not been observed for elastomers. For the first time necking is observed for a lightly cross-linked poly(dimethylsiloxane) elastomer filled with 30 phr or more of high surface area (≥300 m2/g) fumed silica. A series of linear and nonlinear mechanical properties of the necked material were studied including (i) linear and nonlinear dynamic shear analysis including the Payne effect, (ii) uniaxial tension experiments including the Mullins effect, (iii) tensile strength, and (iv) tear resistance via the ‘trouser’ test. The tensile strength of the necked material was found to be significantly higher than that for non-neck forming systems. The observed necking behavior is consistent with deformation induced aggregate breakage.