Tensile Properties, Single Crystals Temperatures

In a very extensive study of both stress relaxation and dynamic mechanical properties in simple extension, on single crystal mats of fractions of linear polyethylene, Takayanagi and collaborators were able to combine data at different temperatures by reduced variables over most of the range from 16°C up to the temperature of crystallization and also to show that the dynamic and transient data corresponded fairly closely, provided the latter were corrected for nonlinear behavior by an extrapolation procedure to zero strain. It is characteristic of crystalline polymers that departures from linear viscoelastic behavior appear at very small strains, and are sometimes significant in stress relaxation even at a tensile strain of = 0.001. In dynamic measurements, the strains are usually small enough to fall within the linear range. 

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