INFLUENCE OF COMPOSITE FATIGUE PROPERTIES ON LIFETIME PREDICTIONS OF SAILPLANES
Keywords:
Structures, Materials, DesignAbstract
Results of fatigue investigations mainly on glass epoxy (Gl-Ep, dry and wet) and glass polyester (GI-UP) are presented as e-N curves and constant amplitude life diagrams. Some minor fatigue data for graphite epoxy (Gr-Ep) are available, too. They are statistically evaluated for 95% survivability and 95% confidence limit. Service life estimations carried out with the wind energy specific standard WISPER on the basis of the linear Palmgren-Miner rule show good conformity with the corresponding load sequence tests. Thus, the same approach was used to assess the fatigue life of sailplanes with a glider mission program for Gl-Ep and GI-UP for various design strain levels. At all levels, the calculated fatigue life of Gl-Ep gliders exceeds that of GI-UP. These results are valid solely for the high-loaded fibers in a pure spar cap. They cannot be applied to the lifetime validation of e.g. a whole wing with its complex stress distribution. A proposal is made for future certification procedures of whole structures.
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