D5.2 - Parameter identification tool for intra-laminar fatigue damage modelling of unidirectional GFRP laminates

Lightweight composite structures have an important role to play in meeting the sustainable energy goals of tomorrow. The implementation of the modelling state-of-the-art in commercial applications is a key activity to improve the performance and design life of these structures. To this end, a semi-empirical framework is implemented in the Simcenter Samcef commercial finite element code using the intralaminar fatigue damage model and the cycle-jump algorithm that were developed by van Paepegem. An additional parameter identification tool is developed to reverse engineer the material-specific parameters of the model based on data from four-point flexural experiments. A sequence of five specific layups are tested using a laminated GFRP material used in wind turbine blades, which consists of non-crimp fabric plies. The model is validated by comparing simulated and experimental results using digital image correlation for a sixth layup that is selected to be more representative of structures in service.

The implemented modelling framework was able to correctly identify the parameters that govern the stiffness degradation observed during the first two stages of a typical fatigue curve. However, the parameters governing failure in stage III were not correctly identified given that the selected material failed with a significant interlaminar shear component, which the van Paepegem model was not designed to handle. A new coupon design free of stitching could be instrumental in supplying intralaminar failure data for future combined inter- and intralaminar modelling approaches.