PSI - Issue 33

ScienceDirect Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com Procedia Structural Integrity 33 (2021) 1225–1234

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2452-3216 © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the IGF ExCo 10.1016/j.prostr.2021.10.140 2452-3216 © 2021 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review Statement: Peer-review under responsibility of the scientific committee of the IGF ExCo 2452-3216 © 2021 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review Statement: Peer-review under responsibility of the scientific committee of the IGF ExCo Fracture toughness is a resistance to a failure of a structure with a crack-like flaw. The evaluation method of fracture toughness was begun to be propose in the middle of 19 th century. The CTOD test is one of the universal fracture toughness tests which measures the opening displacement of the fatigue crack tip introduced in a specimen. During the CTOD test a phenomenon which is called pop-in sometimes occurs which is found by Boyle (1962). A pop-in is an arrested brittle crack behavior itself with a drop in load and increase in clip gauge displacement. Often Fracture toughness is a resistance to a failure of a structure with a crack-like flaw. The evaluation method of fracture toughness was begun to be propose in the middle of 19 th century. The CTOD test is one of the universal fracture toughness tests which measures the opening displacement of the fatigue crack tip introduced in a specimen. During th CTOD te t a phenome on which is called pop-in sometimes oc urs which is found by Boyle (1962). A pop-in is an arr ted brittle crack havior itself with a rop in load a d increase in clip gauge displacement. Often © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the IGF ExCo Abstract A pop-in is a small, arrested brittle crack occurs during a fracture toughness test. This is one of the important factors of the CTOD assessment of a welded joint because the fracture toughness of a material differs by the significance of the pop-in. The current standard of the pop-in is said to be too conservative because of the reasons below; the absence of the test specimen which ensures pop-ins, and the difference of the loading mode between the CTOD test and the real structures. The objective of this study is to investigate the mechanism of the pop-in formation and to improve the pop-in acceptance criteria. Firstly, experiments are carried out with the “brittle bead specimen” which is a welded specimen that artificially represents the local brittle zone so that the pop-in stably occurs. From the result of the experiment, the standard of the load drop ratio of the pop-in can be set as 10% from the current 5%. Next, the finite element method analysis is performed to see the difference of the loading mode of the bending and tensile. From the result of the FEM analysis, it is suggested that the previous research of the pop-in is incorrect and the new model of the pop-in formation with the parameter of the width of the local brittle zone is proposed. Abstract A pop-in is a small, arrested brittle crack occurs during a fracture toughness test. This is one of the important factors of the CTOD assessment of a welded joint because the fracture toughness of a material differs by the significance of the pop-in. The current standard of the pop-in is said to be too conservative because of the reasons below; the absence of the test specimen which ensures pop-in , and the difference of the loading mode between the CTOD test and the real structures. The objective of this study is to investigate the mechanism of the pop-in formati n and to improve the pop-in acceptance criteria. Firstly, experiments are carried out with the “brittle bead specimen” which is a welded specim n that artificially represents t local brittle zone so that the -i st bly occurs. From the result of the experiment, the standard of the load drop ratio of the pop-in can be set a 10% from the current 5%. Next, the finite element method a alysis is perf rmed to see the difference of the loading mode of the bending and tensile. From the result of the FEM analysis, it is suggest d that the previous research of the pop-in is incorrect and t e new model of the p p-in formation with the parameter of the width of the local brittle zone is proposed. Keywords: pop-in ; brittle fracture ; steel ; CTOD test ; ISO standard ; crack arrest IGF26 - 26th International Conference on Fracture and Structural Integrity Investigation of Pop-in Formation Mechanism in Fracture Toughness Test of Welded Joint and Revision of Acceptance Criteria IGF26 - 26th International Conference on Fracture and Structural Integrity Investigation of Pop-in Formation Mech nism in Fracture Toughness Test of Welded Joint and Revision of Acceptance Criteria Toru Yagi* ,a , Yasuhito Imai b , Tomoya Kawabata a a the University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8654, Japan b Tokyo Gas Co., LTD, 1-5-20 Kaigan Minato-ku, Tokyo 105-8527, Japan Toru Yagi* ,a , Yasuhito Imai b , Tomoya Kawabata a a the University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8654, Japan b Tokyo Gas Co., LTD, 1-5-20 Kaigan Minato-ku, Tokyo 105-8527, Japan Keywords: pop-in ; brittle fracture ; steel ; CTOD test ; ISO standard ; crack arrest 1. Introduction 1.1. Background 1. Int oduct on 1.1. Background