ECN publication
Method to predict fatigue lifetimes of GRP wind turbine blades andcomparison with experiments
Published by: Publication date:
ECN Energy Efficiency in Industry 1996
ECN report number: Document type:
ECN-RX--96-036 Other
Number of pages: Full text:
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A method to predict fatigue lifetimes of fiber reinforced plastics inwind turbine blades is described. Measured fatigue properties of a material are taken into account so that credit can be given to materials with improved fatigue properties. The large number of test results should also give confidence in the fatigue calculation method for fiber reinforced plastics. The method uses the Palmgren-Miner sum to predict lifetimes and is verified by tests using well defined load sequences. Even though this approach is generally well known in fatigue analysis, many details in the interpretation and extrapolation of the measurements need to be clearly defined, since they can influence the results considerably. The following subjects will be described: method to measure SN curves and to obtain tolerance bounds, development of a constant lifetime diagram, evaluation of the load sequence, use of Palmgren-Miner sum, and requirements for load sequence testing. The fatigue lifetime calculation method has been compared with measured data for simple loading sequences and the more complex WISPERX loading sequence for blade roots. The comparison is based on predicted mean lifetimes, using the same materials to obtain the basic SN curves and to measure laminates under complicated loading sequences. 7 figs., 5 tabs., 24 refs.

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