PSI - Issue 33

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Toru Yagi et al. / Procedia Structural Integrity 33 (2021) 1225–1234 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The results of this new model are shown in Fig. 16. The green line represents the section notch specimens since the width of NRL-S is 2mm in the experiment, and the blue line represents the surface notch specimens of the experiment. This model can explain the actual experiment in chapter 2. From this result, it is suggested that the brittle crack is more likely to arrest in bending mode than tensile mode in case of the straight crack shape, but 3D tunnel crack shape effect helps to enhance arrest ability in both modes, bending and tension. And it becomes clear that LBZ width requirement is important for the pop-in crack arrest ability when the judgement condition in standards will be discussed.

4. Conclusion In this study, the following points are concluded. •

According to the novel experiments which induces pop-ins and a numerical model that is combined FEM analysis and simplified SIF calculation, it was revealed that the current requirement in major standards for pop in judgment was too conservative. • The previous study of reflected stress wave is not an appropriate theory to describe the pop-in crack arrest. • The pop-in crack arrests by the closing effect of the side ligament which comes from the fact that the pop-in crack is a tunnel crack. The width of the local brittle zone is an important parameter for the pop-in standard. • New proposal of the judgment criterion is that if the width of the LBZ is less than 2 mm, pop-in of less than “10%” of the load drop can be ignored. Boyle, R W; Sullivan, A M; Krafft, J M: 'Determination of plane strain fracture toughness with sharply notched sheets'. Welding Journal, Vol. 41 (September 1962), p.428. Kamath, M.S. and Gittos, M.F.: The incidence of Pop-ins in fracture toughness testing, The Welding Institute Res. Bull., April (1979), 114. ASTM E399- 70T; “Tentative method of test for plane strain fracture toughness of metallic materials”, (1970) M.G. Dawes, Quantifying Pop-In Severity in Fracture Toughness Tests, Fatigue Fract. Engng. Mater. Strurt. Vol. 14, No. 10, pp. 1007-1014, 1991 British Standards Institution, Methods for Plane Strain Fracture Toughness, ( K IC ) Testing, DD3 (1972) British Standards Institution, Methods for Crack Opening Displacement, (COD) Testing DD19 (1972). British Standards Institution, Methods of test for plane strain fracture toughness ( K IC ) of metallic materials, BS 5447:1977 British Standards Institution, Methods for crack opening displacement (COD) testing”, BS 5762, 1979. British Standards Institution, Method for determination of K IC , critical crack tip opening displacement (CTOD) and critical J values of fracture toughness for metallic, BS7448 Part 1, 1991 ISO 12135. Unified method of test for the determination of quasistatic fracture toughness. Geneva: International Organization for Standardization,2002, 2016. K. Arimochi and K. Isaka, A Study on Pop-in Phenomenon in CTOD Test for Weldments, Transactions of the Japan Welding Society, Vol. 20, No. 2, October 1989 Arimochi, K. and lsaka K. A Study on Pop-in Phenomenon in CTOD Test for Weldment and Proposal of Assessment Method of Significance of Pop-in, IIW Doc. X-1118-86 (1986) ASTM E208-20, Standard Test Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels, ASTM International, West Conshohocken, PA, 2020 Imai, Y., Kawabata, T., 2019. Yosetsu Kouzou Symposium. Osaka, Japan. Rose, L.R.F., 1976. An Approximate (Wiener-Hopf) Kernel for Dynamic Crack Problems in Linear Elasticity and Viscoelasticity. Proceedings, Royal Society if London. Vol. A-349. Willoughby, A. A., 1986. Significance of Pop-in Fracture Toughness Testing, International Journal of Fracture 30. References