Demonstration by test of the fulfilment of damage tolerance requirements for an oxygen feeding line bracket of the main cryogenic stage of Ariane 5 launcher

Paper number

IAC-06-C2.1.07

Author

Mr. Bernard Campion, EADS Astrium, France

Year

2006

Abstract

The oxygen feeding line of the Vulcain 2 engine of the main cryogenic stage of Ariane 5 is linked to the engine thrust frame by the mean of five machined brackets made of aluminium alloy. Each bracket constitutes a single load path submitted to quasi-static and dynamic loads coming from the line. As a consequence, a failure of any of the brackets can lead to the failure of the line itself and then to a loss of the launcher mission. Hence, in addition to the stress verification, Ariane 5 dimensioning rules require damage tolerance analysis of the brackets.

The last simulation loop of the dynamic behaviour of Ariane 5 Evolution led to an increase of the dynamic loads on the oxygen feeding line brackets. In particular, the analysis of the crack propagation using Esacrack and Nasgro softwares showed that the upper bracket could fail before the end of the dimensioning life considering the initial crack defect size (1.8 mm) that can be detected by non destructive inspection (NDI).

Unfortunately, at the time of this analysis, the main cryogenic stage was completely integrated and there was no solution to reinforce the bracket or to perform finer NDI.
As it was considered that the Nasgro analysis could be very conservative, it was decided to perform a damage tolerance test, in flight configuration, on brackets coming from the same material batch as the bracket integrated on the launcher.

A quarter circular notch has been machined in a lug of the bracket, considered as the most critical area, in the same configuration as for the damage tolerance analysis. Then tensile/compressive load cycles were applied to the bracket to initiate the crack. The initiation was controlled by propagation gauge at the surface of the part. Once the crack has been initiated, the in-flight load spectrum has been applied to the bracket as in the calculation. Finally the test demonstrated that the bracket could withstand the dimensioning spectrum without failure and that its life duration was, at least, two times greater than the duration calculated with Nasgro. As the bracket integrated on the launcher was machined by the same process from the same material batch and had been submitted to the same NDI, it was concluded that it was flight worthy.

Abstract document

IAC-06-C2.1.07.pdf

Manuscript document

IAC-06-C2.1.07.pdf (🔒 authorized access only).

To get the manuscript, please contact IAF Secretariat.