Postbuckled Stability of Panels with Torsional Buckling

The panel analysis and optimization code VICONOPT, based on exact strip theory, is utilized to investigate the postbuckling stability of a stiffened aerospace panel in a torsional buckled state. The paper shows that the postbuckling characteristics of a panel buckling in a torsional mode has similarity to the postbuckling behavior of a panel with a skin initiated mode and a panel initiated mode. The postbuckled stiffness of the torsional mode is similar to the skin mode in terms of load versus end shortening and is similar to the panel postbuckling behavior in terms of load versus out-of-plane deflection. If the panel has stiffeners of more than one size then there are multiple torsional modes. For panel design it is suggested that small stiffener buckling, i.e., in a torsional mode, can have postbuckling stability with regard to the growth of the out-of-plane deflection. If the large stiffeners initiate the buckling then there is no postbuckling reserve of strength. This has implications for design of such panels as mass could be saved if allowance is made for small stiffener buckling in the optimization process. I