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.