Fatigue Life Improvement of Metallic Aerospace Structures via Crenellations
In a former study it was shown that systematic thickness variations (crenellations) can improve the fatigue crack growth (FCP) life of the integrally stiffened aluminum panels significantly . The source of this improvement is the stress intensity factor (K) modification due to the geometry change caused by implementation of the crenellations. The crenellation pattern controls the K-modification and therefore indirectly the FCP life improvement that can be achieved. In the current study, the limits of this improvement were investigated by optimizing the crenellation pattern numerically. For the optimization, finite element analysis (FEA) and artificial neural networks (ANN) methodologies were utilized in a coupled way. The life calculations were performed according to the Paris Law considering uniaxial and biaxial loading conditions. In the second part, an additional mechanism contributing to the life extension on the crenellated panels, namely loading history effects, explained with the help of the specially designed FCP tests. It was demonstrated that the fluctuation of the K-factors on crenellated panel leads to significant crack growth retardation, which improves the FCP resistance of the panels further. Finally, the application potential of crenellated panels under the more service-related condition of biaxial loading is discussed in conjunction with a currently running research program.
KeywordsStress Intensity Factor Fatigue Life Crack Length Fatigue Crack Growth Reference Panel
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