Tensile Mechanical Properties of PEEK Films Over a Wide Range of Strain Rates. II N. D. ALBE ´ ROLA, P. ME ´ LE ´ , C. BAS Laboratoire Mate´riaux Polyme`res et Composites, Universite´ de Savoie, Campus Scientifique, Baˆtiment IUT, F-73376 Le Bourget-du-Lac Cedex, France Received 19 June 1996; accepted 18 September 1996 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 05 to 300 s 01 . 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 05 to 10 s 01 , the strain rate dependence of both apparent Young’s modulus and yield stress is weak; and 2) from 10 01 to 200 s 01 , both parameters signifi- cantly 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 tem- perature could be governed by similar molecular mechanisms as those giving rise to the b 1 and b 2 transitions. The Eyring analysis shows that motions of five or six mono- mers 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 con- cerned. 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. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1053 – 1059, 1997 Key words: poly ( aryl ether ether ketone ) ( PEEK ) ; dynamic mechanical relaxation; mechanical behavior INTRODUCTION break of amorphous PEEK aged at temperatures below T g . Moreover, these authors have found a significant decrease in the fracture toughness of Few works deal with the tensile mechanical be- such aged samples with an increase in the aging havior of amorphous PEEK. Cebe et al. 1 have keeping time. shown that amorphous PEEK films drawn at low Other amorphous polymers also show changes strain rates, i.e., 0.5 s 01 , exhibit a high drawabil- in the tensile mechanical behavior with an in- ity even at low temperatures. Thus, strain at crease in the experimental temperature and the break of amorphous PEEK tested at 257C is about strain rate. The origin of such a transition in the 270% and it is not significantly decreased at an mechanical properties has been attributed to the experimental temperature of 01007C. presence of various relaxational processes. 3–6 Furthermore, Kemmish and Hay 2 have shown The influence of the reinforcement effect of the an increase in both the yield stress and stress at crystalline phase on the mechanical properties of semicrystalline PEEK was also analyzed. 7–10 Thus, Cebe et al. 9 have shown that the crystallin- Correspondence to: N. D. Albe´rola. q 1997 John Wiley & Sons, Inc. CCC 0021-8995/97 / 061053-07 ity ratio is not the only parameter governing the 1053 / 8E65$$4014 03-11-97 13:35:05 polaa W: Poly Applied