In this paper, rotating-bending fatigue tests of short carbon-fiber reinforced polyetheretherketone (CFRPEEK) and polyetheretherketone (PEEK) were carried out to investigate the fatigue characteristics of plain and notched specimens at room temperature. The fatigue mechanisms in the matrix and composite was clarified through the successive surface observation using the replica method. The results were discussed using linear notch mechanics. In the plain specimen of PEEK, fracture always occurs from defects and the fatigue crack initiation is of the point-initiation type. Furthermore, the fatigue crack growth rate is very high and the fatigue strength is very sensitive to a notch. The fatigue strength of the composite is much more insensitive to a notch than that of PEEK. In general the fatigue crack initiates from near the fiber end, and propagates to the circumferential direction after it grows to some extent along the fiber. The fatigue strength of an arbitrary notched specimen of these two materials will be estimated from the present results rearranged based on "linear notch mechanics".
High performance composites are being applied to engineering applications such as space vehicles, aircrafts, road transportation, fishing rods, golf-club shafts and yachts because of their ease of fabrication, their light weight, and economy (Broutman and Krock, 1974). Many studies on the fatigue and static fracture of long carbon-fiber reinforced composites have been made to keep structures working safely (Hull, 1981). There are a few studies, however, for short fiber reinforced composites because of its low specific strength, low specific elastic modulus and the complexity of fracture phenomenon due to the source of stress concentration such as fiber end or fiber-matrix interface. It is very important to investigate the fatigue mechanism of the composite for the requirement of reliability in the components.