TIME AND TEMPERATURE-DEPENDENT DEFORMATION OF POLY(ETHER ETHER KETONE) (PEEK)

The stress-strain behavior in tension and the effect of temperature on the creep of poly(ether ether ketone) (PEEK) have been studied. Ar ro om temperature, similar to 130 degrees below the glass-transition temp erature, the material does nor become brittle, and the specimens show necking in tension over a wide range of elongation rates. The stress a nd strain at yield and the strain at break are almost linear functions of the logarithmic elongation rate. The values of stress and strain a t yield increase slightly with increasing elongation rare, while the s train at break decreases markedly. The short-term creep tests were con ducted at temperatures extending from 20 to 200 degrees C. The glass-t ransition temperature was found to be about 155 degrees C. The creep o f PEEK is greatest at temperatures above 130 degrees C. In the glass r egion the time dependence of the deformation is much weaker. Ir has be en found that the time-temperature relation for PEEK corresponds well with its thermorheological simplicity in the temperature range investi gated. The data on the temperature shift factor below and above the gl ass-transition temperature may be fitted separately to the Arrhenius a nd Williarns-Landel-Ferry (WLF) equations, respectively. The long-term creep tests show that PEEK has excellent creep resistance at room tem perature. After 14-month tests at a stress level of 30 MPa the total s train exceeds the instantaneous elastic strain only by a factor of 1.1 5.