A modified composite fatigue damage model considering stiffness evolution for wind turbine blades

Proper fatigue life prediction is very essential for the safety of structural design, operation, and maintenance. This paper presents a modified composite fatigue damage model considering stiffness evolution aimed at simulating the three periods of damage development. The proposed model containing two parameters avoids the trouble and complexity of multiparameter. Meanwhile, the stiffness degradation model and the life prediction model of two-stage loading have a good agreement and high fitting accuracy with experiment data considering different types of composites. For better assessment, four existing models are also compared, demonstrated that the values predicted by the modified model are much closer to the experimental data upon most occasions. Moreover, this model is applied to the fatigue test of a full-size wind turbine blade to show its availability and future prospect on real-time monitoring in service.