Improving the fatigue performance of airframe structures via the hybridized application of geometrical modifications and laser heating

Abstract

This study aimed to investigate an optimization method that can maximize fatigue crack retardation based on the concepts of crenellation and residual stress engineering. By applying both concepts, fatigue crack retardation was achieved by the systematic modulation of the panel thickness and by the superposition of a beneficial residual stress field induced by laser heating. To identify an optimized implementation of both concepts, an advanced finite element method-genetic algorithm coupled approach was proposed, where each possible configuration in terms of the crenellation geometry and the positioning of the laser heating lines was encoded in a binary string. The inclusion of the residual stress field induced by the laser heating in the finite element method model was achieved by the inherent strain approach. It was found that the optimized configurations showed from 38% up to 77% fatigue life extensions, which were much larger than the linear superimposition of the fatigue life improvements by each individual technique.