Abstract:
With the PTFE membranes as the research object, the uniaxial stress relaxation tests were carried out respectively under 5 temperatures (23, 40, 50, 60, 70 ℃) and at 4 initial tensile rates (2, 5, 10, 20 N/s), and the effects of these 2 kinds of factors on the stress relaxation properties of the membranes were investigated. The variations of the relaxation moduli were got and several existent viscoelastic constitutive models were used to fit the experimental data. The results show that, the PTFE membranes exhibit obvious stress relaxation behaviors. Both the temperature and the initial tensile rate have significant effects on the stress relaxation characteristics. The membrane stress relaxation rate decreases while the final steady stress increases with the temperature; on the other hand, the final steady stress decreases with the initial tensile rate while the stress relaxation rate keeps almost unaffected. Most of the existent viscoelastic models, esp. the fractional exponent one, make good predictions for the stress relaxation behaviors of the PTFE membranes, while some models work ill due to their poor compositions.
