On the scatter factor in fatigue testing of composite material structures

摘要

Composite materials are widely used in the aviation industry in recent years. Among theiradvantages are their superior fatigue characteristics. Fatigue substantiation of the airframestructures should be carried out by tests or analysis supported by test evidence. Since largescale tests are conducted on a single test article, possible scatter due to material andmanufacture variability must be accounted for by means of application of scatter factors onthe design life goal of the product. It is commonly agreed that the scatter in compositematerials is greater than that of metals and a scatter factor of 13.3 on the lifetime of thecomposite structure is often conservatively employed. In this paper, the fatigue life scatterfactor is discussed and reassessed in light of fatigue tests carried out on 25 material andspecimen configurations. The modified Joint Weibull approach has been adopted to calculatethe scatter factor and the corresponding fatigue life factor. The combined life-loadenhancement factor is also discussed as a measure for test duration shortening. Finally,recommendations regarding the reassessed fatigue life factor for full scale testing arediscussed.