Fatigue of composites for wind turbines blades

This chapter aims to provide an overview of the current design and testing approaches, discuss their limitations, and sketch a future multiscale approach that links models and tests at various length scales. We start from the loads on blades, and how blades are manufactured, then describe how blades fail, and the damage types that blades can develop. We discuss full scale blade testing methods as well as testing of substructures and element test specimens. We emphasis the necessity of connecting length scales (multiscale testing and multiscale modelling), and the importance of connecting experiments and models. The long-term goal is to establish experimental and modelling tools that enable the modelling of damage growth for blades individually in accordance with the digital twin concept. The input to the digital twin will be sensor input from the physical blade, so that the damage state can be modelled individually for the individual blade.