Improved approach for the panel buckling calculation of stiffened shell structures with torsional stiff stringer

Abstract

Primary structures of aerospace applications are often constructed as stringer frame stiffened shell structures because of their high load carrying capacity. Recent research activities on the design of such shells have shown that the design is a demanding task due to the mostly interdependent design variables. Furthermore, the calculation of panel instability is only possible with numerical simulation software demanding high computational costs. Recently, an efficient approach was developed with promising results. This work is taken up to be analysed in more detail. Study structures with differentiating stiffnesses are defined. Findings show high deviations in the prediction of panel instability for increasing axial stiffness of the shell. The reason is found to be the insufficient consideration of prebuckling deformations resulting from the reduced structural model. Improvements to the method are suggested: The reduced structural model is changed and the formerly Ritz formulation is converted into a finite element formulation. One panel of the shell is discretized by the derived one dimensional element. The influence of skin buckling on the structural behaviour is taken into account. An adapted smeared stiffener theory is used in an iterative calculation routine. Geometrically non-linear verification computations are conducted using commercial finite element simulation software. The suggested adjustments lead to a capturing of the size effect and a significant improvement of the method. Excellent results for the prediction of panel instability with reasonable error margins are delivered.