Entwicklung einer miniaturisierten bruchmechanischen Probe für Nachbestrahlungsuntersuchungen

Abstract

The present report introduces a miniaturized sample for the determination of fracture mechanics characteristics of ferritic-martensitic steels. Due to its small dimensions and the geometry selected, the three-point bending specimen is suitable for use in irradiation programs with limited space. The non-conservative results which are feared to be obtained when using small specimens are prevented by a geometrical modification of the fracture zone and by the development of a suitable test and evaluation technique. An experimental and computational validation on the basis of standard samples using different materials reveals the validity of the fracture mechanics characteristics obtained with such samples. An analysis of the stress state in front of the crack tip, based on finite-element calculations, suggests artificial constraints by lateral notches. Such notches give rise to stronger uniformly distributed stress states and J-integral values under mode-I loading for samples of different sizes, which are useful for the determination of fracture mechanics characteristics. Isothermal experiments are performed under the three fundamental material conditions of ductile, brittle, and ductile-to-brittle-transition using different specimen sizes and geometries. The shift of the fracture toughness' ductile to brittle transition - in comparison to full-scale specimens - is examined in tempered experiments. It is shown that considering the recommendations for evaluation given in this report, non-conservative results can be excluded. Practical suitability of the specimen type presented is demonstrated by examining irradiated samples. Evaluation shows that the specimen is - also under the conditions of hot cells and remote handling -usable for fracture mechanics investigations and that it supplies reproducible values for J I D and K I D .