AbstractWhen an uncompounded elastomer is processed on a two‐roll mill, four different regions of mechanical behavior are observed, depending upon the temperature and the severity of the nip deformation. this behavior is observed on materials with a wide variety in chemical composition, through the severity varies. The flow at high temperatures is typical of melt or polymer solution behavior. At lower temperatures unstable flow and elastic solidike regions are observed. By presuming the elastomer to be an isotropicviscoelastic medium, the stress and velocity fields were computed in the polymer melt region. The unstable regime was found to correspond to a critical value of the ratio of viscoelastic to viscous forces. The mathematical analysis, done interms of the Green‐Rivlin‐Noll theory of viscoelastic media, extends earlier studies of deformation in this geometry by Gaskell and B
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