Study on Fracture Assessment (3rd Report)

Abstract

Japan Welding Engineering Society (WES) standard WES 2805 gives procedures for safety evaluation of defects at elastic-plastic condition in welded structures on the basis of the CTOD concept. The essential point of fracture strength assessment in WES 2805 is a relationship between CTOD value and local applied strain, so called “CTOD design curve”. It is important to confirm the applicability of local strain based CTOD design curve to the case of the structural stress concentration, because most of brittle fractures in real structures occur from the defects at the structural stress and strain concentrated region.In this series of studies on fracture strength assessment, an investigation on fracture test results for some kind of structure models with strain concentration was carried out, and modified WES CTOD design curve was proposed. Furthermore, wide plate tests with cracks emanating from a hole and stiffener model tests with a crack in the strain concentrated region were carried out, and applicability of the proposed CTOD design curve was investigated.In this study, wide plate tests with stress concentration using 2-dimensional finite element analysis were carried out, and it was shown that the relationship between CTOD and local strain was varied with the relative size of the plastically deformed region as compared with defect size. It the plastically deformed region size was lagerer than 4 times of crack length, modified WES CTOD design curve under-estimates CTOD value. It has been revealed that the proposed modified WES CTOD design curve is valid for fracture strength assessment of cracks in the stress concentrated region except above mentioned case.