The influence of thermal history on the mechanical properties of poly(ether ether ketone) matrix composite materials

The purpose of this study is to provide insight into the microstructural factors that affect the flexural fatigue performance of carbon-fibre-reinforced poly(ether ehter ketone) (PEEK) composites. Specifically, the effect of the degree of crystallinity on the mechanical properties is examined at two crystallinity levels of the as-received composites (35%) and of quenched composites (10%). Higher static flexural strength and modulus as well as longer fatigue life are observed for the higher crystallinity level. By varying the loading angle with respect to the fibre direction it is shown that the crystallinity effect is not matrix dependent alone. Rather, a strong effect is evident in the fibre direction, which is attributed to the influence of the transcrystalline layer formed on the fibre surface in the high-crystallinity material. As a result, the longitudinal fatigue life at 1·7GPa of the 35% crystallinity material is three orders of magnitude higher than that of the 10% crystallinity composite.