Crack Paths 2009
[56]. Then it is assumed that o-pr : o'mmif 0min >o-Op. The following relation specifying
the crack growth per one cycle was proposed in [19]:
§N—°= Corr. 'r (20) where r is length of decohesion zone along the crack growth direction and C, n are the fatigue parameters obtained from uniaxial tests (or = 90°). In the case Ti-6Al-4V alloys the fatigue parameters are: 3.5 and 1.712. The comparison of model predictions and experimental results are shown in Tables 2 and 3. The comparison with predictions of R-criterion is also presented in tables in the following form 0'" > O, (21) where C1,n1 are the fatigue constants for the uniaxial test (or : 90°). In the case Ti-6Al 4V alloys the parameters are l,26-lO’14and 5.4 respectively [57]. In the uniaxial test equation (21) is equivalent to Paris equation. RIGTHTIP. (Eq. 21) RIGHTA N DLEFTTIP. (Eq. 20) RIGHTTIP (Experimental results from [52]) t 1 da/dN \ 1 da/dN \ r da/dN La L N La Z N La L N [10'3m] cykle [10a'7m] [10'3m] cykle [10'7m] [10'3m] cykle [10'7m] 0,945 3583 2,64 0,945 1390 6,77 0,91 1390 6,54 1,705 5416 4.15 1,705 2430 6,25 1,70 2430 7,59 l 4,58 8695 l 13.83 4,58 5 400 12,14 4,55 5 400 12 l 6,86 9813 | 24,89 6,86 7 000 18,38 6,86 7 000 18 Table2. Mixedmodefatigue crack growth in titanium alloys for specimen A. R I G T HTIP. (Eq. 21) R I G H TA N DL E F TTIP. (Eq. 20) R I G H T IP (Experimental results fr6m [52]) 1 1 da/dN a N da/dN a N da/dN La Z N [10'3m] cykle [107m] [103m] cykle [107m] [103m] cykle [10'7m] 0,86 3546 1,64 0,86 2 954 2,91 0,30 4 660 1,85 3,575 12862 4,19 3,575 9 804 4,91 3,00 11 490 5,77 4,435 14462 5,72 4,435 11 268 6,15 3,87 13 000 3,91 6,9 17436 10,36 6,9 14 319 9,54 6,33 15960 10,92 Table 3. Mixedmodefatigue crack growth in titanium alloys for specimen B. 255
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