A novel model for determining the fatigue delamination resistance in composite laminates from a viewpoint of energy

A previous study indicated that the normalized fracture controlling parameter (strain energy release rate G normalized by fatigue delamination resistance Gcf) in the Paris-type law has advantages of lower exponents and data scatter to evaluate the fatigue delamination growth (FDG) behavior. To accurately determine the critical Gcf, which characterizes the real changing resistance against delamination growth, a novel model is proposed from a viewpoint of energy. This model also allows the judgement on the numerical equivalence between the Gcf and fracture toughness Gc in a simple way. Well-designed delamination tests under mode I loading were carried out to validate the model. Significant R-curve effects on the FDG behavior due to fiber bridging and the bridging difference between static and fatigue delamination at the same delamination length were observed. The calculated result of Gcf has a really good agreement with that obtained by the compliance method, which indicates that fatigue delamination resistance can be accurately determined by using the present model.