Researching the non-linear geometrical effects caused by static flap-wise loading of a wind turbine blade

Many questions exist regarding the structural integrity of wind turbine blades, and this thesis aimed to answer some of these as a means to increase future reliability. One of the key problems with the blade structural response under high static loads was the occurrence of a geometrically non-linear bending phenomenon known as the Brazier effect. This research aimed to better understand the consequences of this effect on the lightweight material used, and this was achieved by performing laboratory scale specimen tests on representative material. A key outcome was that the box girder suction side web was identified as a critical component and most likely to fail via an interfacial disbond. A related finding was that the presence of an interlaminar delamination in the sandwich web material would significantly reduce the load bearing capacity of that section of web. The percentage reduction in load bearing ability appeared to be a function of skin to core thickness ratio and delamination size. Another key outcome was the identification that either the growth of matrix cracks or the presence of pre-existing delaminations were paramount in the development of interlaminar cracks in the laminate caps. This research has demonstrated that, should future blade flexibility be increased, reinforcing layers in the cap should be introduced. The suggested design of this reinforcement was a modification to the current layup that introduced transverse layers along the inner side of the cap. This was proven to increase the flexural rigidity by 107%. Additionally, for future blade certification and monitoring, web delaminations should be identified, potentially by use of digital image correlation or acoustic emissions monitoring, both of which were demonstrated as being capable techniques