The skin of an aircraft can vibrate as a result of pressure waves caused by engine and/or aerodynamic effects. In modern 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, 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 to grow.
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