Mode I fatigue delamination growth behavior and model for multidirectional laminates with the same overall stiffness

In order to isolate the influence of ply orientation on the mode I fatigue delamination propagation behavior of carbon fiber reinforced composite laminates, multidirectional laminates with the same overall stiffness are designed while three different interfaces (0//0, 45//45, and 90//90), which can avoid the coupling effect of remote plies. Test results show that the fatigue delamination behavior is obviously affected by the interface angle. In addition, a novel and simple method for determining the fatigue delamination resistance is proposed. The measured fatigue delamination resistance is lower than the quasi-static one for all interfaces. The specimen with 45//45 interface exhibits more significant delamination resistance, whereas the delamination resistances of specimens with 0/0 and 90//90 interfaces are similar, which is consistent with the phenomenon of more bridging fibers accompanying in the delamination process of 45//45 interface. In order to consider the effect of fiber bridging and reduce the dispersion of the data, experimental data are further processed using a normalized model considering the effect of fiber bridging. The normalized results can be characterized by a single curve, suggesting that the normalized model is effective in describing the fatigue delamination behavior in the presence of fiber bridging.