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FROM:
Andreas Rittweger (1), Susanne Christianson (1) and H. Öry (2)
(1) EADS Astrium Space Transportation, 28361 Bremen, D
(2) Institut für Leichtbau, RWTH Aachen, D
“Dimensioning of Orthotropic Stiffened CFRP Shells of Large Launch Vehicle for Load Introduction and Stability”, (publisher and date not given in the pdf file; latest reference is 1991. The work looks much more recent than that, possibly presented at one of the conferences held in Braunschweig, Germany, such as one of the “International Conference on Buckling and Postbuckling Behavior of Composite Laminated Shell Structures”)
ABSTRACT: The dimensioning of an orthotropic stiffened cylindrical CFRP shell subjected to load introduction of concentrated axial loads using rapid analytical methods is presented. The dimensioning considers required constraints in the force flux distribution, strength of the laminate, general instability, panel instability (from ring frame to ring frame) and local instability. The rapid analytical methods allow for mass optimization. The final design is confirmed by detailed FE analysis. A comparison of the FE analysis with the analytical results is shown.
INTRODUCTION: Primary structures in launcher rockets consist of orthotropic stiffened shells. In order to meet lightweight targets more and more CFRP shell designs are used. For example, in the upper composite of the Ariane 5 (upper stage and payload area) all primary structures, except the propellant tanks, are built of CFRP.
The Ariane 5 design of these orthotropic stiffened shells is buckling and stiffness driven. High concentrated loads due to the load introduction of the booster propulsive loads must be carried and distributed into the structure.
The solid booster loads of Ariane 5 are introduced in a cylindrical shell, the so called JAVE (Front Skirt), which is an orthotropic stiffened metallic shell (aluminium). The JAVE is connected with a 5.4 m diameter CFRP made cylindrical sandwich shell, called ISS (Inter Stage Skirt), which carries axial force fluxes due to the load introduction of more than 1000 N/mm.
For the study of a future launcher based on Ariane 5 elements, called WOTAN, the axial force fluxes introduced in the 5.4 m diameter cylindrical shell are up to 5300 N/mm. The high force fluxes have to be attenuated on an acceptable level within an axial length of only 4.5 m until entering the propellant tank structure.
Different CFRP designs are possible for the cylindrical shell: Sandwich design (CFRP face sheets with metallic honeycomb core), stringer and ring stiffened skin (all in CFRP) or a corrugated CFRP shell stiffened by CFRP rings. The design choice and the mass optimization have to consider a huge set of variable parameter and design criteria such as: 1. Axial force flux distribution (which depends on the design or stiffness, respectively), 2. Strength of the laminate, 3. General instability of the cylindrical shell, 4. Panel instability (from ring frame to ring frame), 5. Local instability.
The presentation describes the approach for dimensioning and optimization. For the parametric investigation rapid tools have been used which base on the analytical solution of shell differential equation. The rapid tools allow the dimensioning and mass optimization with an affordable effort and in a systematic manner. The final chosen design has been investigated in detail with a complex Finite Element Model. The FE model confirmed the results of the simplified tool. Comparisons of results achieved with the simplified method and with the detailed FE model are presented.
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