Ductile Tearing Prediction of Ferritic Pipes by GTN Model for ATLAS+ European Project (Report 2)

Abstract

The European project “Advanced Structural Integrity Assessment Tools for Safe Long Term Operation (ATLAS+)” is aiming to achieve a reasonable balance between safety and long term operation of nuclear reactor pressure coolant boundary systems. In the project, the Work Package 3 deals with development and validation of finite element analysis (FEA) using the Gurson-Tvergaard-Needleman (GTN) model to predict a ductile crack growth behavior of a pipe structure from those of laboratory specimens such as SE(T) and C(T) specimens. By using the parameter sets of the GTN model obtained by other members in the project, the authors predicted the fracture behaviors of three pipes with a circumferential through-wall crack or a circumferential outer surface crack by the four-point bending test conducted by a member of the project. As a result, the predicted maximum loads agreed with those of experiments within the error of 2.2 %, and the predicted ductile crack growth amounts were nearly equal to those on the fractured surface. In addition, the J-resistance of the pipe with a though-wall crack was calculated by the FEA by the node release technique with a crack growth criterion according to the crack growth predicted by the GTN model. Consequently, the J-resistance of the pipe is 3.1 to 3.6 times larger than that of C(T) specimens, which means that a prediction by the conventional fracture mechanics has a lot of margin to the actual fracture behavior.