Developments in dual-axis cyclic fatigue testing
Latest issue / 2 April 2012 / Dr. Richard Court, Technology Specialist at the New and Renewable Energy Centre (NaREC); Dr. Robert Dominy, Reader in thermodynamics and fluid mechanisms in the School of Engineering at Durham University and Peter Greaves, Research Postgraduate in the School of Engineering and Computer Sciences at Durham University
The blades of a wind turbine are undoubtedly one of its most critical components. Catastrophic failure of one blade can lead to the destruction of the whole turbine and damage to the surroundings. For this reason, full-scale tests are performed on turbine blades as part of the certification process, to ensure that they are fit to survive the in-service loadings. These tests usually involve mounting a blade horizontally from its root and applying appropriate loads to it.
Static tests are generally performed by attaching wooden saddles to the blade at several points along its length. The saddles are shaped so that they fit snugly around the blade profile. Winches attached to the saddles are then used to load the blade such that the bending moment distribution matches as closely as possible the loads that the blade sees in service.
Cyclic loading fatigue tests can also be performed. The importance of this fatigue test increases as the blades grow in size. Fatigue has long been recognised as an important part of blade design, but because the blade needs to be stiff to stop it striking the tower during an extreme gust of wind, it was often the case on shorter blades that fatigue was not the dominant design driver. However, as blades get larger (e.g. above 60m lengths) the selfweight loads start to cause the blade to become fatigue critical. (more…)
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