Prediction of cleavage crack propagation path in a nuclear pressure vessel steel

A propagation criterion based on maximum principal stress is proposed to predict the cleavage crack propagation in a nuclear vessel steel. Experiments are performed on three specimen geometries: standard Compact Tensile, precracked ring (mixed mode) and Extended Compact Tensile. Their crack paths are respectively directionally stable and straight, directionally stable and curved, directionally unstable and deflected. Numerical computations are performed by eXtended Finite Element Method. The propagation criterion, combined with a deterministic direction criterion based on the maximum hoop stress provides good predictions for directionally stable crack paths whereas predicting directionally unstable crack paths requires a probabilistic direction criterion.