ATLAS+ European Project - General Method for the Components J-R Curve Derivation

Abstract

The main objective and mission of the European Project ATLAS+ project was to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems. ATLAS+ WP3 was focused mainly on ductile tearing prediction for large defects in components. Several approaches have been developed to accurately model the ductile tearing process and to take into account phenomena such as the triaxiality effect, or the ability to predict large tearing in industrial components. These advanced models include local approach coupled models or advanced energetic approaches. Unfortunately, the application of these tools is today rather limited to R&D or expertise. However, because of the continuous progress in the performance of the calculation tools and accumulated knowledge, in particular by members of ATLAS+, these models can now be considered as relevant for application in the context of engineering assessments. Although there are analytical solutions for calculation of J-Integral values for many standard specimen geometries (i.e. CT or SENT), limited or no formulas are available for more complex structures such as pipes, elbows, T-junctions, pressure vessels etc. Therefore, there is a need to develop a methodology which can be used for derivation of J-R curves for an arbitrary component geometry on the basis of experimental results obtained by testing small size laboratory specimens. To achieve this goal Framatome GmbH used combined local approach (GTN model) and elastic-plastic calculations to determine J-R curves whereas Framatome France used analytical methodologies to derive the J-R curves from local approach results (GTN model). In both cases, the Δa and J values were calculated at the deepest point of the crack front. This paper shows promising results and concludes there is a significant margin in the fracture mechanics assessment based on material properties obtained by testing highly constrained standard specimens compared to more realistic structural situations.