The strain-rate and temperature dependence of the mechanical properties of polyetherketone and polyetheretherketone

The mechanical properties of polyetheretherketone and polyetherketone were studied asa function of strain rate and temperature in the ranges 10(-3) to 10(3) s(-1) and 20-200 degrees C. At temperatures below the glass transition temperature, T-g, the strain-rate sensitivity of both polymers was found to be almost independent of temperature with a value of similar to 4MPa per decade of strain rate and the behaviour was well described by an Eyring relationship leading to an activation volume of similar to 1 nm(3). Above T-g, X-ray and differential scanning calorimetry studies show that cold-crystallization phenomena play a very important part in the polymer behaviour, leading to an increase of yield stress with increasing temperature, The crystallization was found to be highly strain-rate dependent with no increase in crystalline content occurring in quasi-static tests and increases of up to 20% in higher rate tests. Much of the data have been gathered using novel test equipment which is described in the paper.