FINITE-ELEMENT ANALYSIS OF BONDED REPAIRS TO EDGE CRACKS IN PANELS SUBJECTED TO ACOUSTIC EXCITATION

The skin of an aircraft can vibrate as a result of pressure waves caus ed by engine and/or aerodynamic effects. In modern fighter aircraft su ch as the F/A-18, sound pressure levels have been recorded up to 170 d B over the surface of the skin. In the F/A-18 cracking has occurred in the lower nacelle, typically along the boundaries of the panel. These cracks often originate from a fastener line, grow along the boundary and then turn into the centre of the panel. In the case of the F/A-18, cracking was due to higher than expected pressure levels caused by an aerodynamic disturbance at the inlet lip. Attempts have been made to repair these panels with boron fibre patches, however the cracks have continued ts grow. This paper aims at attempting to understand the mec hanisms of cracking of the panels subjected to acoustic excitation and the influence of bonded repairs. Also, the analysis is extended to a feasibility study on the effects of enlarging the patch and increasing material damping on the stress intensity factor. (C) 1997 Elsevier Sc ience Ltd.