PSI - Issue 2_B

J.-J. Han et al. / Procedia Structural Integrity 2 (2016) 1724–1737

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J-J Han et al. / Structural Integrity Procedia 00 (2016) 000–000

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Fig. 5. Notch C(T) specimens: e ff ect of radius on tearing resistance curve and fracture toughness (API X65).

notch tip radius, ρ (with 0.2 mm ≤ ρ ≤ 2 mm):

J ρ IC / J IC = 5 . 342 ρ + 0 . 306 J ρ IC / J IC = 2 . 890 ρ + 0 . 734 J ρ IC / J IC = 2 . 576 ρ + 0 . 710 J ρ IC / J IC = 2 . 828 ρ + 0 . 734

(APIX70) (APIX65)

(4)

(INCONEL617)

(SA508Gr . 3)

Results from the analysis led to the following outcomes:

• Fracture resistance curves ( J − R curves) predicted with the ductile fracture model shows excellent agreement with curves derived from load-load line displacement data according to ASTM E1820-13e1 (Figure 5) • It was shown that increasing notch root radius (i.e. blunting the notch), led to an increase in the e ff ective fracture toughness at both ductile initiation (defined at an engineering definition of 0.2mm of crack growth) and the subsequent resistance to ductile tearing (the J-R curve) • These observations led to an increase in reserve factor when accounted for in a FFS assessment using the FAD. As expected, a blunt notch shows lessened likelihood of crack-dominated failure than a sharp crack. . It is also observed that the e ff ective fracture toughness linearly increases with notch radius (Figure 6 and Equations 4). • It was shown that the Option 1 Failure Assessment Diagram (FAD), developed for sharp cracks and used in most FFS codes, is also relevant to blunt notched C(T) specimens (Figure 7.a). • The approach presented here may be applied with the FAD method to define a notch radius above which analysis may be based simply on plastic collapse, without the need to consider ductile fracture initiation (see Figure 7.b) • The degree of conservatism in assuming a blunt defect as sharp was quantified by a reserve factor on the fracture parameter K r , used in FAD methods and the results showed that the reserve factors could be increased by up to