Development of a test for the analysis of the harmfulness of a 3D thermal fatigue loading in tubes

The incident which has occurred on the Civaux power plant has shown the nocivity of thermal loading and the difficulty to take it into account at design level. The objective of this paper is to study the initiation and the propagation of crack under thermal loading. In this aim the CEA developed a new experiment named FAT3D. The various experiments carried out showed the harmfulness of a thermal loading, which makes it possible to rapidly initiate a network of cracks and to propagate one (or some) cracks through the total thickness of the component under certain conditions. These experimental results associated with a mechanical analysis question the usual criteria of damage based on the variations of the equivalent strain. In addition, the study of the propagation stage shows the capability of classical models to estimate crack growth.