CONSTRAINT BASED EVALUATION OF CRACK GROWTH EXPERIMENTS IN THE TRANSITION REGION

— A large number of experiments has been performed over a wide temperature range in the transition region of a ferritic steel with the aim of studying its fracture behaviour and assessing the applicability of a two parameter fracture mechanics approach for such situations. The experimental results clearly show a constraint effect, reflected in a decrease of the transition temperature with a decrease in specimen size and in a narrower transition region for shallow cracks. The results also show that the J ‐ Q model, in conjunction with a fracture criterion (like the RKR criterion for cleavage fracture) is a promising approach for predicting the cleavage fracture event even in the transition region. No constraint effect could be detected for ductile initiation. The cleavage stress has been measured directly by testing. This reduces the number of fracture tests needed for the construction of the critical J ‐ Q locus and improves the accuracy of the predictions.