STRUCTURAL INTEGRITY ASSESSMENT OF BIMETALLIC WELDS WITH CENTER AND INTERFACIAL CRACKS

Abstract

The structural integrity assessment of cracked mismatched/bi-metallic joints is an important issue for the nuclear industry. Recent international surveys of such welded joints have shown that there are several cracking problems, due to fabrication, ageing or corrosion. Thus there exists a strong need to develop simple methods to assess the fracture integrity of such bi-metallic joints. In this work closed form solutions are developed for evaluating plane strain limit loads of deeply cracked mismatched/bi-metallic fracture specimens: the single edge pure bending specimen (SEPB), three-point bend specimen (TPB) and compact tension specimen (CT). Three possible crack locations are considered: the weld center crack, crack at interface between weld metal and weaker base metal and crack at interface between weld metal and stronger base metal. Solutions for crack at locations other than this lie intermediate of the three cases considered. After 'making appropriate simple assumptions, for the cases of wide range of mismatch ratios and weld width accurate closed form solutions for plane strain limit load were obtained for both mismatched and bi-metallic specimens. Moreover plastic n factor values based on CMOD and CTOD which are used for experimental determination of J-integral are provided for all the cases. Detailed finite-element analyses were performed to check the accuracy of the expressions developed. For the purpose of validation, the results obtained by numerical fittings are compared with solutions provided by Y. J. Kim for mismatch cases with weld center crack.