Mechanical Failure in PEEK and Its Short-Fiber Composites

Abstract

Four commercial PEEK systems—two grades of neat PEEK and short GF and CF-fiber composites—were compression-molded. Compact tension fracture tests were performed, with temperature and specimen thickness as variables. The dependences of the critical stress intensity factor K_Q and of mechanical nonlinearity on these variables are re ported. The filled systems show both nearly constant K_Q and low ductility from —90 to +125°C. For all materials, K_Q varies more slowly with temperature than does the tensile strength. Specimen thickness, varied from 0.29 to 1.25 cm, has a profound effect on neat PEEK, as it changes from plane stress to plain strain behavior Thickness has essentially no effect on the composites, which show plane strain behavior over the entire thickness range.