PSI - Issue 5

Yoichi Kayamori et al. / Procedia Structural Integrity 5 (2017) 286–293 Yoichi Kayamori et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 4 Distribution of the plastic strain increment and the total strain increment in the crack opening direction along the ligament on the mid-thickness plane.

4. Discussion

A possible reason why ASTM E1820 (2008) and ISO 15653 Annex-E (2010) have avoided using the plastic hinge model is because a 0 /W and strain hardening affect the plastic rotational deformation of the specimen (1993, 2006), and the accuracy of the plastic hinge model based CTOD seems to be lower than that of the J -integral based CTOD. However, C(T) specimens with a through-thickness crack for CTOD testing usually employ a 0 /W ≈ 0.5, and C(T) specimens will not be used for the evaluation of a surface crack located on the specified microstructure in welded joints. Accordingly, the target of a 0 /W was set at 0.5 in this study. As shown in Fig.5, r p for Y/T =0.6 was almost identical to that for Y/T =0.9, and the effect of strain hardening on r p was accordingly quite small. This suggests that the plastic rotational deformation should be held, and it is feasible to use the plastic hinge model f o r c a l c u l a t i n g C T O D i n C ( T )

Fig.5 Changes in the plastic rotational factor with increasing loading up to 0.2 mm of CTOD.

specimens with a 0 /W ≈ 0.5. The tendency for r p to be stable was recognized for smaller CTOD than 0.2 mm in this study, and the target of fracture toughness evaluation is the critical CTOD for offshore structures. Further investigation should be conducted for the evaluation of ductile fracture with larger plastic deformation.