Prediction of Residual Strength and Curvilinear Crack Growth in Aircraft Fuselages

Two practical engineering approaches to assess the structural integrity of aircraft fuselages are presented. Both approaches combine fracture mechanics with thin-shell finite element analyses to predict structural responses quantitatively. The first approach uses the crack-tip opening angle fracture criterion to predict residual strength of KC-135 fuselages. The second approach uses T-stress and fracture toughness orthotropy to predict crack-growth trajectory in narrow-body fuselages. For residual strength prediction 12 damage scenarios, which might occur in applications, are examined. It is found that the model with small multiple-site cracking and material thinning caused by corrosion damage has the worst load-carrying capacity. For curvilinear crack-growth simulation a directional criterion based on the maximum tangential stress theory accounting for the effect of T-stress and fracture toughness orthotropy is used to predict crack-growth trajectory. Both T-stress and fracture toughness orthotropy are found to be essential to predict the observed crack path, where the trajectory experiences crack turning and flapping phenomena.

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