Supervisors: Associate Professor Lars P. Mikkelsen (DTU Wind Energy), Co-supervisor: Dr. Jens Zangenberg Hansen (LM Wind Power), Senior Scientist, Leon Mishnaevsky Jr. (DTU Wind Energy)
External examiners: Professor Christian F. Niordson (DTU Mechanics), Professor S. Mark Spearing (University of Southampton), Professor Leif Asp (Chalmers University)
Abstract: Fatigue Damage Evolution in Fibre Composites for Wind Turbine Blades
One of the largest challenges in wind turbine design is realistically predicting the life-time of the blade material. Wind turbine blades experience a high number of fatigue load cycles during their life-time, and the fatigue damage mechanisms of the non-crimp fabric based glass fibre composites used for the load carrying parts of wind turbine blades are not well understood.
This PhD project has established experimental methods making it possible to monitor the damage initiation and progression of fibre composites in three dimensions using X-ray computed tomography (CT). To overcome the resolution challenges of X-ray CT, a tension clamp solution that applies load to the specimen during X-ray CT examination is presented, and the advantage of combining X-ray CT with other experimental techniques is demonstrated.
The established methods are used to monitor the damage initiation and progression of fatigue damage on the micro-scale in the non-crimp fabric based composites used in the load carrying part of a wind turbine blade. By monitoring the damage initiate and progress in 3D, it is found that under fatigue loading the damage initiate and progress as local 3D phenomena. The damage affected regions gradually grow in size and connect to one another eventually resulting in final failure, which aside from providing valuable knowledge on the damage mechanisms in the investigated materials, also show the importance of considering fatigue damage in all three dimensions.
The knowledge obtained on the fatigue damage mechanisms during the project can not only be used to improve the materials, but also sets the stage for X-ray CT based modelling. This is a step towards more realistic fatigue life-time predictions of fibre composites used for wind turbine blades, which will make it possible to push the design limits of wind turbine blades and thereby decrease the cost of energy for the wind energy production. In addition to the above mentioned achievements, the experimental methods established during the PhD project can be applied to a large variety of cases, material systems, and load conditions opening up for many new opportunities.