The effect of crystallinity on fatigue properties of glass fiber reinforced poly (ether ether ketone) composite materials

Glass fiber reinforced poly (ether ether ketone) (GF/PEEK) composite materials with different crystallinity were manufactured by controlling the cooling rate of the hot pressing process. Then, two crystallinity kinetics equations were used to analyze the non-isothermal crystallization process of the GF/PEEK composite materials. In addition, the effect of PEEK resin matrix crystallinity on the fatigue properties of composite materials was further revealed through the tension-tension fatigue test in this study. The crystallization kinetics showed that the nucleation mode of the GF/PEEK composite materials was mainly heterogeneous nucleation. Moreover, the crystallinity and crystal size of the composite materials decreased with the increase in cooling rates. Meanwhile, the fatigue failure modes of the composite materials could be observed in the fatigue failure microstructure figure, which included matrix cracking, interface failure, fiber debonding and fiber fracture. It had been found that crystallinity greatly influences the fatigue properties of composite materials. In the GF/PEEK composite materials with low crystallinity, the surface of failed fibers became rough or even adhesion to the permanently deformed resin matrix with a wide range of plastic yield. Moreover, the fatigue crack passes the amorphous phase more quickly, resulting in more significant residual stiffness degradation and shorter fatigue life.