On the Cold Drawing of Poly-Ether-Ether-Ketone (PEEK) Tubes

The mechanical behaviour commonly referred as cold drawing (CD) is a phenomenon that occurs once the yield point is reached, in a thermoplastic material subjected to a uniaxial tensile test at constant strain rate. In effect, after yielding the sample undergoes a neck in its cross-sectional area, which then propagates along the entire useful length of the sample while the applied force remains constant. This phenomenon occurs in amorphous or semi-crystalline materials in a wide range of temperatures below the glass transition temperature. Understanding this phenomenon involves knowing what deformation mechanisms operate and how they are related to the morphology of the material. In this work, on one hand, the mechanical response of poly-ether-ether-ketone (PEEK) thermally aged at 25 and 135 °C for 30 day is measured. In previous researches PEEK aged at 130 and 135 °C undergoes cold drawing when subjected to a tensile strain rate of 1,7 10-3 s-1 at 25 °C. In addition, the average stress and the ultimate elongation of the plateau depend on the temperature and the duration of the annealing. On the other hand, wide angle X ray diffraction, density measurements, differential thermal analysis, shape memory analysis and complex impedance measurement allow determine changes in the amorphous and crystalline phases due to thermal aging and cold drawing effects.