21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-5.3.2

OPTIMIZATION OF A COMPOSITE BONDED REPAIR TO CRACKED PANELS SUBJECTED TO ACOUSTIC EXCITATION

Callinan R. J., Chiu W. K.*, Galea S. G.
Aeronautical & Maritime Research Lab., Australia; * DSTO, Australia

Keywords: optimization, composite bonded repair, cracked panels, acoustic excitation

The skin of an aircraft can vibrate as a result of pressure waves caused by engine and/or aerodynamic effects. In modem fighter aircraft such as the F/A-18, sound pressure levels have been recorded up to 170 dB over the surface of the skin. In the F/A-18 cracking has occurred in the lower nacelle external skin, typically along the boundaries of the panel. These cracks often originate from a fastener line and grow along the boundary and then turn into the centre of the panel. In the case of the F/A-I8, cracking was due to higher than expected pressure levels caused by an aerodynamic disturbance at the inlet lip. An attempt was made to repair a panel with a boron fibre patch however this repair did not appear to significantly reduce the crack growth. The design of the repair was based on in-plane loads only. This paper aims at developing a patch design, based on a finite element analysis, which significantly reduces crack stress intensity factor for structures subject to intense acoustic environments. A significant reduction in stress intensity is achieved by using a highly-damped patch which incorporates a uni-directional boron/epoxy repair surrounded by viscoelastic material, which provides the necessary damping, and [0/90] boron/epoxy constraining layers.

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