Future structural stability design for composite space and airframe structures

Abstract

Space and aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite space and aerospace struc-tures contributes to this aim, however, it requires accurate and experimentally validated stability analysis. This paper deals with advances and challenges related to coupled stability analysis of composite structures. Thin-walled light weight structures endangered by buckling can be for in-stance divided into two groups: imperfection tolerant and imperfection sensitive structures. For both groups design guidelines for composites structures are still under development. This paper gives a short state-of-the-art and presents proposals for future design guidelines. Imperfection tolerant structures are for instance stiffened panels as used in aeronautic applications. The maximum load is quite insensitive with respect to imperfections. Such structures are characterised by a relatively large postbuckling area which is usually used for designs in metallics but not composites. There are some finished and running European projects (e.g. COCOMAT, MAAXIMUS) to this topic which are summarized shortly. Imperfection sensitive structures are for instance unstiffened structures or stiffened structures with a rather dominant skin compared to the stiffeners. For such structures the maximum load is equal or close to the first buckling load and is imperfection sensitive. These types of structures are commonly used in space applications. The currently applied design guidelines with respect to structural stability were developed only for metallic structures and are from 1968. For composite structures no guidelines exist. The “Single Pertubation Approach” is a promising concept for future applications but on the other hand it opens a lot of new questions. The paper presents this approach, results as well as the challenges for the future.