first published

A large fatigue crack in the wing skin of an Australian Defence Force F-111C aircraft was repaired with an adhesively bonded boron/epoxy fibre composite patch. The patch prevented further growth of the crack for 670 flying hours. To aid in the continued safe operation of ADF F-111 aircraft, a decision was later made to assess the residual life of the F-111 wings in part by undertaking a fatigue test at DSTO on a retired wing. An additional aim of the test was to substantiate further the bonded repair, in view of its potential application to other F-111 aircraft either as a repair for cracked wings or as reinforcement to inhibit fatigue crack formation in uncracked wings. The test importantly would also evaluate the effectiveness of non-destructive inspection (NDI) and other non-destructive procedures to detect crack growth under the patch or disbonding of the patch system. The repaired wing was therefore selected and used for this study. In this test the patch was successful in preventing growth of the crack for around a further 9000 simulated flying hours. As a consequence of NDI indications of local patch disbonding and concern that it could lead to rapid growth of the repaired crack and thus premature failure of the wing a structural health monitoring (SHM) technique was implemented to monitor the patch