Creep may be defined as the deformation observed in a sample versus time under a constant applied stress. PEEK polymer has outstanding creep resistance for an engineering thermoplastic material and may sustain large stresses over a useful service life without significant time induced extension. Figures 6 and 7 display the creep behavior of PEEK 450G with respect to applied stress, time and temperature.

The magnitude of stress, time and temperature required to induce accurately measurable (>0.5%) strains is exceptionally large for an unfilled polymer. Values of creep modulus (E_s) may be calculated from such data and used as a measure of resistance to creep deformation. The creep moduli for some of the high performance compounds from the PEEK polymer grade range are plotted against time in Figure 8.

From the data in Figure 8 it is clear that reinforcement significantly enhances the excellent creep resistance of PEEK™ polymer and that the carbon fiber based compounds (CA30) are the highest performance materials tested.

If analogous plots to Figures 6 and 7 are constructed for 450CA30 (Figures 9 and 10), the time dependent strain behavior over experimentally practicable lifetimes may be evaluated. From the data shown in Figure 9 it is clear that there is little measurable creep at ambient temperatures even for the highest values of stress (7250 psi) applied to the 450CA30 samples.

At elevated temperatures (Figure 10), under the same applied stresses, small but measurable time dependent strains are observed. Although the creep resistance of natural PEEK polymer is outstanding for an unfilled material, 450CA30 can be used to make structural components which will withstand continual loading over a wide temperature range.

Information reprinted with permission from Victrex PLC