PSI - Issue 13

Khalid Eldwaib et al. / Procedia Structural Integrity 13 (2018) 444–449 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

448

5

( d d ) = ( +1 − )

(2) where ( d d ) is crack growth rate per each propagation step; is step number, and is number of estimated load cycles per each step. Obtained results are presented in Figure 5 and Figure 6

0.0E+00 5.0E-05 1.0E-04 1.5E-04 2.0E-04 2.5E-04 3.0E-04 3.5E-04 4.0E-04 4.5E-04

Main integral spar U-section spar

Intermediate flange (1) Intermediate flange (2) Intermediate flange (3)

da/dN (mm/cycles)

Fig. 5 Comparison of d ⁄d calculated per each step of crack propagation (crack length 0 – 12mm) 0 1 2 3 4 5 6 7 8 9 10 11 12 crack length (mm)

5.0E-05 1.5E-04 2.5E-04 3.5E-04 4.5E-04 5.5E-04 6.5E-04 7.5E-04 8.5E-04 9.5E-04 1.1E-03 1.2E-03 1.3E-03 1.4E-03 1.5E-03 1.6E-03 1.7E-03 1.8E-03 1.9E-03 2.0E-03 2.1E-03 2.2E-03 2.3E-03 2.4E-03

Main integral spar U-section spar

Intermediate flange (1) Intermediate flange (2) Intermediate flange (3)

da/dN (mm/cycles)

12

13

14

15

16

17

18

19

20

Fig. 6 Comparison of d ⁄d calculated per each step of crack propagation (crack length 12 – 20mm) In Figures 5 and 6 significantly higher CGR values can be observed for cases A, B, and C 1 , compared to small CGRs in cases C 2 and C 3 . For small cracks’ lengths (Fig. 5), differences in CGR values are not significant, but after 3mm cases C 2 and C 3 become very different from the other three. Cases A, B and C 1 have similar CGR values until 8 mm and then main integral spar values (case A) start to grow faster than the others. Differences become even greater when cracks reach lengths higher than 12mm (Fig. 6), while the greatest difference can be seen at a=20mm: CGR in case C 3 is about 2 × 10 −4 ⁄ , though CGR in case A is almost ten times bigger ( 2.2 × 10 −3 ⁄ ). crack length (mm)