Aerospace industry moves to carbon fibres

With financial support from the EU's Clean Sky Joint Technology Initiative (JTI), a consortium was assembled to assess if aircraft panels made of CFRPs can withstand the ultimate loads expected during service. The aim of the 'Fatigue test' (FATIGUETEST) project was to develop the experimental set-up to record and analyse their long-term behaviour.

Multi-step tests were carried out on five prototype aircraft panels with integrated stiffeners, designed and manufactured by FATIGUETEST partners. In addition, small piezoelectric sensors were embedded in the panel laminate to detect elastic waves generated by the rapid release of energy from sources within the CFRP material. Sources of acoustic emission include plastic deformations and fracture.

Complementing other non-destructive testing methods, acoustic emission and acousto-ultrasonics technology is sensitive enough to detect newly formed cracks, long before structural integrity is compromised. Notably, FATIGUETEST researchers opted not to test the carbon fibre panel to failure.

The custom-made test rig for static and dynamic loading of the panel consisted of two clamping devices and one anti-buckling device. The strains induced with a hydraulic servo-cylinder monitored and measured in real time. The huge amount of data recorded was then analysed and correlated against finite element models and simulation analysis of the panel.

Successful completion of the fatigue test by the fifth and final aircraft panel marks a major step in determining the strength of aircraft structures made of composite materials. The test rig and methodology proposed by the FATIGUETEST project is expected to go on to form part of future certification test programmes.