13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- 5.2. Damage tolerance analysis of an aircraft component A damage tolerance analysis (DTA) was carried out for the CW-1 critical location of the CC-130 center wing, made of 7075-T7351 plate, illustrated by the sketch in Figure 12. Since the DTA involves a multiple, phase-by-phase (PBP) crack growth analysis, the NRC in-house tool CanGROW was originally developed for such PBP analysis purpose. Prior to calibrating the CC-130 strain gauge based spectrum, the Hsu retardation model with default parameters was used in the DTA. Again, both the legacy and NRC Forman material models were used for the DTA, and the results are presented in Figure 12-(b). The legacy material model resulted in a fatigue life that was 45% shorter than that of NRC material model. Because multiple site fatigue damage (MSD) was found in-service, the PBP analysis was updated by an MSD analysis, as shown in Figure 13. Using the unique MSD analysis module developed in CanGROW, the legacy material model provided an MSD crack growth life approximately 40% of the NRC material model. However, the MSD life to the critical crack size of 6.2 inches (157 mm) was about 17% less than the PBP life. Currently, these DTA results are considered as preliminary until a component test is available to validate these analyses. 0 1 2 3 4 5 6 7 0.0 0.2 0.4 0.6 0.8 1.0 Crack size (inch) Fatigue Life Ratio (normalized to "NRC Forman Model" PBP result) Legacy Forman Model NRC Forman Model (a) PBP initial cracking model (b) Crack size vs. fatigue life Figure 12. PBP DTA using CanGROW and CC-130 strain gauge spectrum (1-in=25.4 mm) 0 1 2 3 4 5 6 7 0.0 0.2 0.4 0.6 0.8 1.0 Crack size (inch) Fatigue Life Ratio (normalized to "NRC Forman Model" PBP result) Legacy Forman Model NRC Forman Model (a) MSD initial cracking model (b) Lead crack size vs. fatigue life Figure 13. MSD DTA using CanGROW and CC-130 strain gauge spectrum (1-in=25.4 mm) 6. Conclusions Both precracked long crack test (C(T)) and natural small crack test (SENT) have been carried out to generate short-long crack data under various stress ratios. The ACR method, coupled with the ASTM E647 load reduction method, reduced the scatter of crack growth rate data caused by the Lead crack Secondary crack Hole Lead crack Secondary crack Hole Panel Panel
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