A Study on Pop-in Phenomenon in CTOD Test for Weldments

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Small crack-intitiation-arrest events so called Pop-ins often occur at CTOD tests for weldments and CTOD values of such Pop-ins ar usually very small in comparison with those of the following final fractures. Present assessment regards Pop-in as a critical event because the significance of Pop-ins for actual structures hasn't been made clear. Therefore much effort has been made in materials and welding procedure in order to prevent Pop-ins. It is, however, considered too conservative to assess Pop-in as initiation of critical brittle fracture if it has been proved that Pop-in has no influence on the safety of actual structures. And so it is indispensable to clarify the significance of Pop-ins which occur in CTOD tests and to establish their assessment method for the safety of actual structures. In this study Pop-in is regarded as a small brittle crack-propagaiton-arrest event which initiates from local brittle zone in-nevitably existing in weldments, and CTOD tests for welded joints which include an artificial local brittle zone are carried out. Consequently, the conditions under which typical Pop-ins usually occur have been cleared up and influence of local brittle zone on behaviours of Pop-in is investigated. Furthermore dynamic behaviours of Pop-in are made clear experimentally and analytically using a newly developed measuring apparatus and dynamic elastic-plastic FEM code, and the results show existence of Pop-ins which propagate and are arrested under the constant external load condition even in a small sized CTOD specimen. These investigations clarify the conditions under which the Pop-in cracks are surely arrested in an infinite plate under tensile load. Finally from the results, an assessment method for singificance of Pop-in is proposed from a viewpoint of brittle fracture.
社団法人溶接学会の論文
1989-10-01

A Study on Pop-in Phenomenon in CTOD Test for Weldments

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