RELATIONSHIP BETWEEN THE TENSILE AND STRESS RELAXATION BEHAVIOUR OF POLYPROPYLENE

Abstract

The mechanical response of real polymers are basically of nonlinear character, therefore their behaviour patterns do not meet the idealized (linear) ones, especially in case of larger loads. Nevertheless, the linear viscoelasticity is often used successfully for describing the real behaviour in case of small or moderate loads. In this paper a way is sought and followed to estimate the real tensile load response by using the linear viscoelastic response given to the real relaxation stimulus and its relationship to the linear viscoelastic tensile load-strain curve and also by using some nonlinear transformations. Experiments were performed on PP as a test material and the stress relaxation behaviour, as well as the linear elastic and linear viscoelastic approximation of the tensile load-time curve were analysed. In order to demonstrate the applicability of this idea and to perform the numerical calculations a flexible function with three parameters was chosen to realize the nonlinear behaviour.