PSI - Issue 42

5

Toru Yagi et al. / Procedia Structural Integrity 42 (2022) 702–713 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2.1 Joint geometry of the brittle bead specimen (this figure shows section notch)

(a)

(b)

Fig. 2.2 Schematic image of fracture surface of (a) a section notch specimen and (b) a surface notch specimen

2.2. Experiment In this experiment, the bending test is the representative of the CTOD assessment, and the tensile test is the representative of the real structures based on the similarity of the loading mode. The bending test and tensile test on both section notch and surface notch of standard specimen whose 0 /W is 0.5 are carried out. The tensile test on shallow section notch specimen whose 0 /W is 0.3 and 0.15 are also performed. The size of the specimen, notch, and the fatigue pre-crack are shown in Fig. 2.3, The test temperature is from 0 ℃ to -60 ℃ . The results are shown in Fig. 2.4. (a) compares the load drop ratio and the CTOD value of pop-ins. 100% of load drop ratio means the complete fracture, and 0% means the specimen experienced the ductile fracture. The point of CTOD is when the maximum load is observed. The data includes all temperatures, -20 ℃ , -40 ℃ , -60 ℃ . No section notch specimen fractured completely. There are some section notch specimens whose load drop ratio of a pop-in is more than 10%. Some surface notch specimen fractured completely in brittle manner. From the results of the section notch specimens, it is suggested that when the specimen experiences a pop-in with around 10% of load drop ratio, the crack would arrest itself in the real structures. (b) compares the standard three-point bending test whose 0 /W is 0.5 and the three-point bending test of shallow notch specimens whose 0 /W is 0.15 and 0.3. The vertical axis and the horizontal axis are the same as the previous comparison. The figure shows the results of the temperature of 0 ℃ and -20 ℃ . Some shallow specimens at lower than -20 ℃ fractures completely in brittle manner. The maximum load drop ratio of CTOD test at -20 ℃ is 21.4%. Shallow