The first scenario presented in Figure 3 is the un-repaired service
life. In this scenario, there is no applied patches. The loading on the
wing structure is continuously applied. Crack is initiated based on the
fatigue damage. BRSW process begins once the wing structure is damaged
with a crack; the loading continues to evaluate the fatigue crack
propagation. Finally, the service life is estimated based on the crack
growth until failure.
The second scenario presented in Figure 3 is the live crack repair. In
this scenario, once the aircraft structure is damaged with a crack from
fatigue, a bolted repair patch is directly applied to the crack (shown
in Figure 4a). Upon the application of the patch, the crack propagation
is estimated with future fatigue loading. Finally, the service life is
estimated for the bonded repair of a live crack using a patch.
The third scenario presented in Figure 3 is the crack removal repair. In
this scenario, prior to a patch bonded repair as in the second scenario,
the damage is physically removed. The crack removal can be performed in
the forms of stop-drill (Figure 4b) or damage-removal (Figure 4c). In
the stop-drill crack repair, two holes are drilled at both ends of the
crack. In the damage-removal crack repair, the crack itself is removed.
For each of these forms of the repair, cracks/damage are re-initiated.
Crack propagation is continued to be assessed and their service lives
are estimated due to fatigue loading.