Tensile mechanical properties of PEEK films over a wide range of strain rates. II

Abstract

Tensile mechanical properties of poly(aryl ether ether ketone) (PEEK) films showing different thermal histories have been investigated at room temperature to point out the main key microstructural features governing properties over a wide strain rate range, i.e., from 10−5 to 300 s−1. The strain rate sensitivity of the mechanical properties of amorphous PEEK films significantly depends on the analyzed strain rate range: i.e., 1) from 10−5 to 10 s−1, the strain rate dependence of both apparent Young's modulus and yield stress is weak; and 2) from 10−1 to 200 s−1, both parameters significantly increase. Thus, based on the definition of the relationships between temperature, strain rate, and frequency respectively used for tensile tests and dynamic mechanical spectrometry, it was shown that the mechanical behavior of PEEK films at room temperature could be governed by similar molecular mechanisms as those giving rise to the β1 and β2 transitions. The Eyring analysis shows that motions of five or six monomers are implied at the beginning of the plastic deformation of amorphous and semi-crystalline PEEK films, while at higher strain rates, shorter chain segments are concerned. Thus, the crystalline phase only induces an increase in the stress level because of the reinforcement effect but does not modify the molecular mechanisms governing the plastic deformation of PEEK films at room temperature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1053–1059, 1997