TEMPERATURE EFFECT ON IMPACT FRACTURE-TOUGHNESS AND FRACTURE MECHANISM OF PHENOLPHTHALEIN POLY(ETHER KETONE)

Phenolphthalein poly(ether ketone) (PEK-C) was tested using an instrum ented impact tester to determine the temperature effect on the fractur e toughness K-c and critical strain energy release rate G(c). Two diff erent mechanisms, namely the relaxation processes and thermal blunting of the crack tip were used to explain the temperature effect on the f racture toughness. Examination of the fracture surfaces revealed the p resence of crack growth bands. It is suggested that these bands are th e consequence of variations in crack growth along crazes that are form ed in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle o f crazes to nucleate along which the crack advances.