Impact of corrugations on bifurcation and thermoelastic responses of hat-stiffened panels

The thermoelastic response of aerospace structures is significantly influenced by structural nonlinearities and conventional design tools based on assumption of linearity prove to be insufficient. A nonlinear analysis of the thermoelastic response of aerospace structures opens up the possibility to capture the rich bifurcation behaviour of such panels. The primary objective of this paper is to study the impact of non-linearity and local geometric features, particularly corrugations, on the themoelastic response and bifurcation characteristics of a hat-stiffened panel. The study derives its motivation from the SR-71 Blackbird that was designed with corrugations in the upper and lower wing skins. A representative hat-stiffened panel is created with corrugations on the skin face-sheet and stiffeners, similar to those on the SR-71 skin panels. The amplitude of these corrugations is varied and the panels are loaded till the bifurcation point is reached. The results show that in the absence of corrugations (at face-sheets) the panel experiences two bifurcation points. The first is similar to the bifurcation predicted from a typical linearized buckling analysis and is surrounded by stable equilibrium branches such that a small perturbation causes the panel to switch to this branch. The second bifurcation point is surrounded by unstable subcritical branches and a perturbation can cause violent snap-through. Adding a face-sheet corrugation causes the first bifurcation point to disappear and the temperature for the second bifurcation point to increase monotonically with the amplitude of corrugation. The displacement and stress at the panel mid-point for a given temperature also reduces with increasing corrugation amplitude. The corrugation in stiffeners does not provide any tangible benefit within the scope of this study.