Figure 5 BRSW simulation on cracked aircraft pressured fuselage repair with repair patch in 3D analysis.
The damaged fuselage skin modeled is 600 by 300 mm and 1mm thick, with a center crack of about 55mm long. The skin material is Al 2024-T3. The titanium repair patch is 155 by 155 mm2 andbolted onto the damaged structure skin (Figure 1). A typical pressurized fuselage loading scenario is applied with 150MPa pressure along peripheral direction and 50MPa in longitudinal direction. In this case study, Titanium alloy was used for the repair patch material and the patch is 1mm thick. Here, four cases are examined; among them three crack treatments are considered in bolted patch repair:
  1. Un-repaired cracked structure where there is no crack treatment is performed at all (fatigue crack propagation analysis is conducted in BRSW)
  2. Live crack repair where patch bonded crack treatment (Titanium patch) is performed (fatigue crack propagation analysis is conducted in BRSW)
  3. Stop-drill crack repair where crack front is drilled w/ stop hole in addition to Titanium patch bonded repair (fatigue damage analysis followed by crack propagation analysis in BRSW)
  4. Damage-removal crack repair where crack region is cut out in addition to Titanium patch bonded repair (fatigue damage analysis followed by crack propagation analysis in BRSW)
For comparison, the fatigue crack growth and service life estimation on cracked skin for the un-repaired case is first analyzed as a reference. A thru-the-thickness crack of size 53.4mm is initially inserted on the wing structure, as shown in Figure 6a. Figure 6b shows the fatigue crack growth of 5.3mm after 1027 service cycles, Figure 6c shows the crack growth of 49.1mm, reaching a total crack length of 102.5mm after 4064 service cycles where it is considered structural failure [20] and the skin to be replaced. Figure 6d shows the service life estimation in the relationship between fatigue crack growth and continued loading cycles. It is evident that BRSW FEA process is able to predict the fatigue crack growing direction deviating from its initial pre-crack orientation, driven by the practical service loading.