TENSILE MECHANICAL-PROPERTIES OF PEEK FILMS OVER A WIDE-RANGE OF STRAIN RATES .2.

Tensile mechanical properties of poly(aryl ether ether ketone) (PEEK) films showing different thermal histories have been investigated at ro om temperature to point out the main key microstructural features gove rning properties over a wide strain rate range, i.e., from 10(-5) to 3 00 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 o f 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 ra te, and frequency respectively used for tensile tests and dynamic mech anical spectrometry, it was shown that the mechanical behavior of PEEK films at room temperature could be governed by similar molecular mech anisms as those giving rise to the beta(1) and beta(2) transitions. Th e Eyring analysis shows that motions of five or six monomers are impli ed at the beginning of the plastic deformation of amorphous and semicr ystalline PEEK films, while at higher strain rates, shorter chain segm ents are concerned. Thus, the crystalline phase only induces an increa se in the stress level because of the reinforcement effect but does no t modify the molecular mechanisms governing the plastic deformation of PEEK films at room temperature. (C) 1997 John Wiley & Sons, Inc.