Rheometers for Biaxial and Planar Extension

To generate equibiaxial extension, sheet inflation, lubricated squeeze flow, and the rotary clamp technique have all been used [9, p. 261]. The most rehable of these is the one based on the rotary clamp technique, and the latest version of this instrument has been described by Hachman and Meissner [160]. This impressive instrument is presently the only rheometer capable of generating homogeneous biaxial extension, but it is somewhat complex and difficult to use. Lubricated squeeze flow is much simpler, but there are important limitations on its capabilities due the difficulty of maintaining lubrication [220].Isakief a/. [161] used lubricated squeeze flow to carry out stress relaxation experiments for determination of the damping 

Planar extension is the most difficult to generate, but two techniques for doing so have been described [ 160,162 ]. No techniques for biaxial or planar extensional rheometry that are suitable for routine use in industry are known at present. 

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