Fatigue crack propagation (FCP) behaviors of mass fraction 15% CTBN (carboxyl terminated butadiene acrylonitrile), 15% Qishi toughening agent toughened anhydride cured epoxy resins (EP), and pure anhydride cured EP were measured. The results showed that the two main toughening mechanisms, localized shear yielding and void plastics growth, which occurred near the threshold region because the rubber size is much less than the plastics size at the crack front, improved the near threshold FCP behavior and increased the threshold. The stable FCP behavior was obviously improved with the FCP rates decreased to less than 21%.
