Assessment of the limitations of the local and global approach criteria in the case of brittle fracture
Congress title :9th European Mechanics of Materials Conference (EMMC9)
Congress location :Moret-sur-Loing
Congress date :09/05/2006
The CEA/SEMT/LISN laboratory has formed a partnership with IRSN/DES/SAMS to seek to understand and confirm the conditions of crack initiation under thermal shock loading. The material in question is a reactor vessel steel, in the brittle/ductile transition domain. The goal of the work is to both understand the particularities of the thermal loading and to assess the transposability of the criteria to the loading configurations. To achieve this objective, the approach adopted has been both experimental and numerical, with the desire to establish pertinent new tests associated with accurate numerical modelling for optimal characterisation of crack initiation conditions under thermal and mechanical loading. In the context of these study, the first set of thermomechanical tests undertaken involved CTT specimens. These tests made it possible to establish, depending on the mode of driving, fracture under cold thermal shock or tests providing evidence of a WPS effect. A second geometry was then proposed, featuring rings subjected to hot thermal shock. This test also made it possible to achieve fracture under thermal and mechanical shock loading. To back up these tests, a number of isothermal tests were carried out to characterise the material as a function of the temperature, and also to explore various issues associated with specific questions relating to the fields of validity of the criteria. It is this last type of exploratory tests that is covered in the article, on basis of analysis of the results obtained with specimens of two different geometries: Tests on CT25 specimens carried out at very low temperature to assess the pertinence of the weakest link hypothesis or confirm the asymptotic value corresponding to the Master Curve. Tests on specimens with semi-elliptical defects, in order to assess the applicability of the criteria to defects with this geometry. For these two series of tests, the observations, the supporting numerical interpretations and the main results obtained are given in detail.