Investigating the fatigue response of wind turbine blades
One of the challenges wind turbines pose from an engineering point of view is dealing with the variable load to which the rotor blades are exposed. This can negatively impact performance and may even lead to premature failure. Such shortcomings hamper the adoption of wind turbines for power production, especially in offshore installations that are not easily accessible. In order to optimise exploitation of available wind energy, the organisations involved in the OPTIMAT BLADES research project sought to address these problems by improving structural predictive methods for blade design. A series of experiments with different blade prototypes was carried out by various partners throughout Europe. Both unidirectional (UD) and multi-directional (MD) laminate constructions were subjected to stresses at pre-defined intervals during their useful lifetime. The OPTIMAT engineers varied the magnitude of the cyclic loads as well as the ratio between the minimum and maximum stress, known as the R-ratio, in order to simulate real-world conditions. Over 700 tests were performed and the results were stored in the OPTIMAT BLADES database. Analysis of the data provided valuable feedback regarding the maximum load that could be sustained without causing breakage throughout the rotor blade's lifetime, defined as its residual strength. In addition, information regarding load sequence proved instrumental for improving models of strength degradation that previously relied solely on Miner's rule.
