Development and test verification of the Ariane 4 interstage 2/3 in CFRP

The interstage 213 of the Ariane 4 launcher has been redesigned in CFRP as an alternative for the original aluminium alloy structure. The objective was to save mass and to demonstrate that costs can be competitive. The application of CFRP is limited to the curved blade-stiffened panels; the ring frames are metal. Initial sizing was performed with simple formulas, while the final design was analysed with NASTRAN and BOSOR4. Flat stiffened panels were tested in compression to verify selected design details of the cylinder. Three different sizes of subcomponent panels were tested to (1) determine the local buckling behaviour, at room temperature and at 180 "C (in accordance with maximum in-flight conditions) (2) determine the strength of the panel to end-ring connections and (3) establish the global panel buckling behaviour between ring frames. Verification tests of the stiffener run-out configuration resulted in a modification to prevent premature separation at the tip. Subsequent tests proved that the modification was adequate. A full scale test on the first article is scheduled for March 1986.