Using the X-FEM method to model the dynamic propagation and arrest of cleavage cracks in ferritic steel

Although initiation criteria have been the subject of many publications, the phenomena associated with the propagation and arrest of brittle cracks have not. To be able to predict the dynamic behaviour of cleavage cracks, we made a series of experiments and associated numerical studies. Tests of crack propagation and arrest were carried out on specimens of two different geometries (Compact Tension and compression ring) made of the 16MND5 ferritic steel of which French nuclear reactor vessels are constructed. The elastic-viscoplastic behaviour of this material was characterised and its nature was taken into account in the numerical simulations. The eXtended Finite Element Method (X-FEM) was developed in CAST3M finite element analysis software to enable fine, effective modelling of crack propagation. Propagation models based on principal stress were studied and it was found that critical cleavage stress depended on loading rate. The use of criteria calibrated for Compact Tension specimens gave excellent results in predictive calculations for similar specimens, and also for compression rings in both mode I and mixed-mode. The speed and path of crack predicted with the numerical simulations were in close agreement with the experimental results.