D5.3 - Unified fatigue damage model and software implementation in SAMCEF

Laminated composite materials are used extensively in wind turbine blades due to their high mechanical performances and good fatigue resistance compared to metals. However, the occurring damage mechanisms are more complex in composite materials due to anisotropy, heterogeneity and defects (due to their nature but also due to the manufacturing process). In order to be able to design safe structures made of composite materials, understanding and predicting the occurrence of damage events and their interplay is essential. This work focusses on the interaction between damage mechanisms occurring at the intra- and inter-laminar regions of the laminate under both static and fatigue loading. A dedicated formulation is developed in order to initiate delamination (inter-laminar damage) from matrix cracking (intra-laminar damage) in the numerical framework implemented in the Simcenter Samcef solver. To this end, the inter- and intra-laminar damage models presented in tasks 5.1 and 5.2 are coupled and synchronized in terms of fatigue cycles. The unified numerical tool is employed to exemplify the predicted mechanical behaviour in an open hole specimen. The results show that the interfacial stiffness is reduced to zero at the regions with high intra-laminar damage, thus modelling a delamination caused by the coalescence of micro-delaminations arising at the crack tips of transverse matrix cracks.