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Analyses of criticality for multiple-site delaminations in the flap spar of Finnish F/A-18 aircraft

Abstract Metal-composite airframes will suffer various defects during their lifetime. One category of defects is composite laminate delamination. This study evaluates the criticality of delaminations existing around adjacent fastener holes in the carbon-fibre-reinforced plastic spar web of the F/A-18 aircraft’s trailing-edge flap. The evaluation is based on experiments and analyses. First, an intensive experimental program for determining necessary material values of F/A-18 is described. Multiple delaminations of the flap spar web are then modelled by varying the set of delaminated hole edges and the interface of delamination. The interaction of defects at the start of delamination propagation is studied via the developed interaction parameter. The results suggest that the interaction parameter can show significant differences in the interaction per delamination case and that the interface of delamination is an important variable. Finally, operator-dependent control parameters are studied, and it is found that the criticality of a delamination case is merely dependent on true material parameters.