Abstract

The various techniques which have been devised to study uniform stretching flows in molten polymers are described briefly, and their advantages and disadvantages are noted. Techniques involving non-uniform deformation such as melt spinning and converging flows are not included as these are not subject to unambiguous interpretation in terms of traditional material functions. Uniaxial extensiometers are either of the controlled stress or controlled strain-rate types. End effects, non-uniformities in temperature and deformation, measurement of very small forces, and limitations on maximum strain are the principal experimental problems. A recent design which seems to keep the effects of these difficulties within reasonable bounds is to be manufactured commerically in the near future. Techniques for the study of biaxial extension have all been based on the inflation of a flat sheet of polymer into a contour approximating a spherical cap. Only one of these techniques is suitable for the study of melts with viscosities less than 10 ⁵ Pa s. An additional method has been proposed which involves the compression rather than stretching of a sheet. Finally, procedures for generating planar extension ("pure shear") and more general extensional flows are described.