Acoustic fatigue is the major damage phenomenon induced by the high frequency lateral vibration of
structural panels, such as that of an aircraft skin, under time varying pressure waves generated by engine and/or
aerodynamic effects. For instance, acoustically-induced cracks have been discovered in the lower external surface
of the nacelle skin and aft fuselage of the F/A-18 aircraft. In the case of the inlet nacelle overall sound pressure
levels of the order of 172 dB have been recorded. Attempts to repair these cracks by applying standard bonded
repairs developed for in-plane loads were made. However the cracks continued to grow at a similar rate as before
the application of repairs. While the repair of cracked aircraft structures subjected to in-plane loads using bonded
repairs has resulted in considerable aircraft life extension and hence cost savings, the use of bonded patches to
repair panels with acoustically-induced cracks (acoustic fatigue) is only recent. In this chapter a generic design
procedure is presented for the repair of aircraft panels containing acoustically induced cracks by incorporating the
constrained layer damping technique. The analytical tools described in this chapter will enable the rapid design of
damped repairs using closed form solutions that account for the effects of high frequency out-of-plane vibration
on crack extension. A case study is also undertaken of a design of a repair to prevent acoustic fatigue cracking on
the aft fuselage of the F/A-18.
