Structural design of Stringer-frame-stiffened shell structures

• Struktureller Entwurf von stringer-spant-versteiften Schalentragwerken

Krause, Max; Schröder, Kai-Uwe (Thesis advisor); Mittelstedt, Christian (Thesis advisor)

Düren : Shaker Verlag (2023)
Book, Dissertation / PhD Thesis

In: Aachener Berichte aus dem Leichtbau 2023,1
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2023

Abstract

The structural design of stiffened shells has been the subject of research for decades. These are often used in the aerospace sector as a design option for primary structures because of their high load-carrying-capacity-to-mass ratio. The importance of structural lightweight design has increased in the design of such structures, because of the increasing commercialisation of the space sector and the accompanying cost pressures for future space launch vehicles. To increase the maximum payload and achieve the ambitious price targets, an optimal design of the structure in terms of lightweight design is imperative. Thin-walled stringer frame stiffened shell structures have the highest load-carrying capacity for use as the primary structures of space launch vehicles. The design of these is complex because of the many failure modes to be considered and therefore requires efficient, robust and reliable design methods. Established methods are unsuitable for modern torsionally stiff stringer profiles, as they do not represent the structural behaviour of the shell adequately. This can also be assumed for prospective profile shapes, which should maximise load-carrying capacity through the highest possible torsional stiffness. In the course of this, the established design process with the aim of an optimal lightweight design must also be questioned, as it is based on the description of the structural behaviour. This work aims to develop new methods for the design of stringer frame stiffened shell structures and to use them to evaluate the necessity of adapting the design process. A structural model is derived to describe the structural behaviour. From this, a method for calculating the panel instability load and a method for the sizing of frames is developed. It is shown that three aspects are responsible for the inadequate nature of the established methods: the neglect of transverse shear, the assumption of the pre-buckling condition as a membrane state rather than a bending state, and the reduction of the stiffened shell to a panel shell. Compared to numerical simulations, the developed methods provide similar accuracy with significantly lower time resource requirements. Finally, the developed methods and evaluated research results are used to propose adjustments to the established design process of stringer frame stiffened shells. Based on the optimisation of a representative shell, the degree of adaptations for an optimal design in terms of lightweight design is evaluated. It is shown that the design process must be thought of in a holistic sense and that a separation of the design of the stringer-skin assembly and the sizing of the frames is not permissible.

Institutions

• Chair and Institute of Structural Mechanics and Lightweight Design [415610]