An analysis methodology for failure in postbuckling skin-stiffener interfaces

Abstract

Blade-stiffened skin designs have the potential to produce highly efficient composite structures provided the large strength reserves available after structural buckling, in the postbuckling range, are exploited. In experimental tests of skin-stiffened composite structures in postbuckling, failure typically initiates at the interface of the skin and stiffener, either around the base of the stiffener or at the edge of the stiffener flange. Delamination or debonding in the skin-stiffener interface typically leads to rapid and even explosive failure of the panel, as the damaged region spreads and leads to a detachment between the skin and stiffener. A methodology has been developed for analysing collapse in postbuckling composite structures that involves detecting the initiation of interlaminar damage in the skin-stiffener interface. A strength-based criterion is monitored in each ply using a local model of the skin-stiffener interface cross section. For the analysis of large structures, a global analysis is first run to get the complete postbuckling deformation field, which is then input onto a local model using a global-local analysis technique. For larger models, the coordinates of the local model can easily be moved to rapidly assess failure initiation at numerous skin-stiffener interface locations throughout the structure. The analysis methodology is compared to experimental results for two-dimensional T-section specimens and large, fuselage-representative stiffened panels and is shown to give accurate predictions of the failure load and failure mechanisms. The use of the approach for the analysis of postbuckling composite structures has application for the design and certification of the next generation of aircraft.