A Contribution Of Environmental Investigations For Glare Riveted Joint Sizing

An extensive experimental research program has been initiated by Delft University in the year 2000 for potential influences of environmental conditions on Standard-GLARE. The investigation covers the whole range of the classical test pyramid from elementary-, via material-, coupon- and component level up to full scale size. The main focus of the exercise is the investigation of potential influences of both, variable temperature and/or environmental exposure on the structural strength justification for static and fatigue properties.

This outdoor exposure program is performed in cooperation with Airbus, who contributes to several investigations, e.g the variable temperature tests and the full scale tests are performed at Airbus. Two structural details which have been part of Airbus full scale tests have been selected for the environmental exposure, i.e. a circumferential joint with a GLARE2 butt strap which has been justified in the A340–600 center section test article and a riveted repair on the full scale research test article “Megaliner Barrel”, made of GLARE4A (see figure 1).

Delft University shipped about 200 GLARE specimens of different sizes and shapes to Innisfails in Queensland, Australia, for environmental exposure. Specimens have been returned after 1, 2 and 6 years, respectively, in order to perform mechanical tests and to compare them with both the as-received specimen and artificially aged specimen. A particular question which is dealt with is, whether the selected artificial ageing process (3000h exposure in 85%/70°C humid air) is representative for the simulation of natural ageing — and if so, for which kind of specimens or structures this might be the case.

The specimens which have been exposed for 6 years in Australia returned in the year 2008. They have been inspected and mechanically tested, i.e. fatigue crack initiation curves for riveted joints in the as-received condition and after 6 years outdoor exposure are now available. However, the inspection procedure, the test procedure and the evaluation of results is often time consuming, especially if micro-fractografic analysis are involved. Therefore not all mechanical test results belonging to this project have been evaluated yet, but some are available for this paper. Selected items will be presented in this paper, which support the strength analysis of the above mentioned GLARE4A repair with special regard to residual strength.