ESTIMATION SCHEMES TO EVALUATE ELASTIC-PLASTICJ AND COD FOR THROUGHWALL CIRCUMFERENTIALLYCRACKED ELBOW UNDER CLOSING MOMENT

摘要

Leak-before-break (LBB) assessment of primary heat transport piping of nuclear reactors involvesdetailed fracture assessment of pipes and elbows with postulated throughwall cracks. Fracture assessmentrequires the calculation of elastic-plastic J-integral and crack opening displacement (COD)1 for these pipingcomponents. Analytical estimation schemes to evaluate elastic-plastic J-integral and COD simplify thecalculations. These types of estimation schemes are available for pipes with various crack configurationssubjected to different types of loading. However, no such schemes are available for throughwallcircumferentially cracked elbow (or pipe bend), an important component for LBB analysis. In this paper, simpleJ and COD estimation schemes are proposed for throughwall circumferentially cracked elbow subjected toclosing bending moment. The ovalisation of elbow cross section has a significant bearing on its fracture behavior.Therefore, unlike conventional deformation theory plasticity analysis, incremental flow theory is adoptedconsidering both material and geometric non-linearities in the development of the proposed estimation schemes.Although it violates Ilyushin's theorem, it has been shown that the resulting estimation schemes is stillreasonably accurate for engineering purposes. Finally, experimentalumerical validation has been provided bycomparing the J-integral and COD between numerical/test data and predictions of the proposed estimationschemes.