PROPOSAL FOR A CERTIFICATION PROCEDURE OF EXTENDED SAILPLANE LIFETIME
Keywords:
Structures, Materials, Design, MaintenanceAbstract
A method is presented to predict the lifetime of sailplanes by the experimental and analytical investigation of spars as their highest loaded primary structure. In this approach, the knowledge about the fatigue behavior of the spar cap or flange and the shear web material is used, since these are the main load carrying fiber components of a spar beam. In an FE (Finite Element) -analysis, the strains of a spar beam are calculated and compared with measurements. On this basis, a lifetime calculation is accomplished for the shear web which is more fatigue-sensitive than the flange. It shows that at those maximum straint the lifetime would achieve the very high and rather academic figure of more than 10 million flight hours. Under application of the linear Palmgren-Miner rule this lifetime corresponds to a load cycle number in a proof test of about 106 when the spar beam is loaded in a monotonic (one-step) fatigue test up to the design load. First results achieved by testing two spars correspondingly, confirm that this method may be a new and beneficial possibility for lifetime approval of sailplanes.
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