The effects of initial nonconstant transient cross‐head speed on the stress–strain curve of viscoelastic material

摘要

AbstractThe effects of initial nonconstant transient cross‐head speed inherent to every tensile tester, especially in high‐speed tension, on the shape of stress–strain curves of viscoelastic materials were studied. In case of brittle polymers, the specimen was subjected to variable strain rates throughout the test loading, although the constant strain‐rate tension is planned, since the cross‐head speed stays within the initial nonconstant transient range due to its small total elongation until fracture and never reaches the prescribed constant cross‐head speed achieved after considerable cross‐head travel. As the polymers were quite strain‐rate sensitive, it was necessary to employ a device to extend the specimen at constant strain rate, i.e., the constant cross‐head speed from the beginning to obtain the stress–strain curve at the exactly prescribed constant strain rate for such brittle polymers. The “slack grip” concept was then introduced and its effectiveness was experimentally verified. In conclusion, the effects of such initial transient cross‐head speed are not negligible for brittle polymers and can be avoided