TENSION-TENSION FATIGUE FAILURE BEHAVIOR OF POLY(PHENYLENE ETHER KETONE) (PEK-C)

Tension-tension fatigue tests were conducted on unnotched injection mo ulded poly(phenylene ether ketone) (PEK-C) specimens with two stress r atios, R. The fatigue behaviour of this material is described. The S-N curves (S = alternating stress, N = number of cycles to failure) for different R values have the same general shape, but the curve for bigg er R is shifted to long cycles. A fatigue lifetime inversion is observ ed from constructed S-N curves. Examinations of failure surfaces and a nalyses of the fatigue data reveal that the fatigue failure mechanism of the material studied is crack growth dominated. But the manner of t he fatigue crack initiation and propagation depends on the maximum cyc lic stress applied. At higher stresses, the fatigue crack originates a t the corner of the specimen and propagates inward; at lower stresses, the fatigue crack nucleates at an internal flaw of the specimen and p ropagates outward. The fatigue lifetime inversion corresponds to the t ransition of crack initiation and propagation from one mode to the oth er. Copyright (C) 1996 Elsevier Science Ltd.