D5.1 - 3D progressive fatigue delamination model

Long fibre-reinforced composite materials are especially suitable for wind turbine blades structural applications due to their outstanding specific mechanical properties compared to metallic alloys. However, composite elements are very sensitive to manufacturing defects and matrix microcracking that can lead to interply delamination and, thus, compromise the structural integrity. Adopting effective and accurate numerical tools able to predict the effects of damage on the carrying load capability of the structure reduces design, certification and maintenance costs. To this end, a fatigue-driven delamination method applicable to the 3D simulation of wind turbine blades is developed. The publications of the method in a scientific paper in a peer-reviewed international journal1 and in the open access archive arXiv2 are outcomes of this sub-task. The method is implemented in the SAMCEF commercial finite element code. A characterization testing campaign on coupon specimens dedicated to obtain the material properties to input the method is carried out. A batch of specimens made of a non-crimp fabric laminated glass fiber reinforced polymers (GFRP) used in SGRE wind turbine blades are tested for each material property. The model is validated by comparing simulated and testing results for a demonstrator specimen with curved delamination front that is selected to be more representative of structures in service. The implemented modelling framework is able to reproduce the experimental results on the demonstrator specimen in terms of crack front shape evolution and crack front location versus number of fatigue cycles with reasonable accuracy. Differences between both results show that the simulation is delayed with respect to the experimental results. However, these differences are deemed to fall within an acceptable range and might be attributed to the high dispersion in the results from coupon specimen used to characterize the fatigue properties of the interface. In any case, the order of magnitude of both result sources is comparable. The simulation tool sets the basis for a powerful tool for fatigue life prediction of laminated composite structure