SIMULATION OF FATIGUE DELAMINATION GROWTH IN COMPOSITES WITH DIFFERENT MODE MIXTURES

A numerical model, obtained by implementing a cyclic damage model in the framework of an interface element, is here proposed to reproduce the crack growth in laminated composites subjected to cyclically repeated loads. This model, which differs from the few studies in the literature on the topic, applies not only to single fracture modes but also to mixed modes, and to constant or variable crack growth rates. The applied load (in terms of force or displacement) is assumed to oscillate between a minimum and a maximum constant value. The Paris curve can be reproduced with accuracy once some parameters in the numerical model are tuned with experiments. These parameters are preliminarily found by simulating fatigue delamination in mode I (DCB test), in mode II (ELS or ENF test) and with a fixed mode mixture sigma = G(II)/G (MMB test). A non-monotonic curve is then used to interpolate these preliminary results. Furthermore, tests where the mode mixture changes with crack length could also be reproduced. With this model it is possible to predict the crack growth rate with cycle of a generic structure without knowing a priori how the mode mixture sigma changes during the crack propagation. This novel procedure gives a new opportunity in the design of composite structures subjected to repeatedly applied loads.