Material CharacterisationEvidences of non-linear short-term stress relaxation in polymers

Back in 1986, investigating the Space Shuttle Challenger disaster, famous physicist Richard Feynman clearly showed how viscoelastic behavior of a polymeric material is of paramount importance in practical engineering. At present day a definitive universal rheological law is not yet available for polymers, as a consequence both theoretical models and experimental investigations of viscoelastic behavior must be necessarily focused independently on each single polymer or, at least, on well-defined classes of polymers. Accurate experimental evidences are needed in order to properly evaluate the mechanical properties of a polymeric material, as a function of its particular applications. In this paper measurements of the stress relaxation behavior of six polymeric materials under uniaxial tension and uniaxial unconfined compression tests, are performed and experimental results are modelled using a stretched exponential function, known as Kohlraush-Williams-Watts time-decay function. In particular the short-term stress relaxation is investigated, as a function of typical environmental temperature range, in order to assess viscoelastic behavior of tested polymeric materials for peculiar industrial and biomedical applications.