Post-buckling of single and multi-bay panels using strut, strip and FE methods

A compressively-loaded stiffened panel has been designed with post-buckling reserve of strength in its skins using the strip program VICONOPT. Comparisons are made with Finite Element single and double bay models. The panel has been shown by VICONOPT to have a stiffener buckling failure mode when an overall sinusoidal imperfection causing increased stiffener compression is present. Such a failure is not seen in a typical single-bay Finite Element model of such panels. However, the failure is confirmed by a double-bay Finite Element model, which is a closer representation of an aerospace application, such as a wing box. A new strut model, following a Shanley type approach has been developed to emphasise the difference between the single and multi-bay responses. The strut model shows good agreement with single bay Finite Element results. It also indicates the presence of an imperfection in the double bay Finite Element model, which may be represented by offsetting the load towards the skin in the strut model. The VICONOPT code is able to design an aerospace panel of realistic dimensions and loading but only when considering linear elastic material properties.