Reduction of fiber pull-out stress due to hot water immersion: Carbon/PEEK

Single fiber pull-out tests have been carried out to investigate the effect of hot water immersion on the carbon fiber/PEEK interface. Although this interface appears to be quite strong and very durable, both the interface and the polymer were slightly weakened and softened by water immersion at 90 degrees C. The interface weakening effect was noticeable after 1 h at 90 degrees C, and there was further slight weakening with prolonged immersion up to 3000 h, with a maximum loss in debonding force of about 33%. For immersion at 60 degrees C the effect was significant only after 1000 h. Polymer softening was noticeable after 1000 h at both 60 degrees C and 90 degrees C. Post debonding friction was also reduced by about 50%. Drying out at 90 degrees C for 360 h did not restore the interface strength or friction, but there was some restoration of the polymer yield stress.