A model of fatigue delamination in composites

In order to calculate fatigue delamination growth in specimens a fatigue delamination growth rate law is needed. To measure the fatigue delamination growth rate experimentally for all possible combinations of energy release rate mode ratios and load ratios would be very expensive. The two constants in the Paris-law equation require that two points on the fatigue delamination growth curve be known. In the model, one such point is the fatigue delamination growth threshold which experimentally has been found to occur for a constant change in energy release rate. The second point occurs when static fracture takes place. From these two points the constants in the Paris-law equation can be calculated for any energy release rate mode ratio and load ratio. The model predicts that the Paris-law exponent n will decrease with decreasing load ratio, Q, and increasing amount of mode II fracture, which agrees well with experimental observations.