Threshold fracture stress: theory and application

摘要

The physical nature of cleavage threshold stress σ_(th) was considered and the technique for its experimental determination was developed. By applying data for reactor pressure vessel steel and cast low-alloyed manganese steel, it is shown that ignoring the value of σ_(th) gives rise to an 1.5-2 times overestimation of the shape parameter m. Within the framework of the suggested alternative of the Local Approach, temperature dependences of fracture toughness KIC for probabilities of 5%, 50% and 95% were obtained for the steels. Accounting for the threshold stress σ_(th) a correct quantification of the temperature effect on fracture toughness values K_(IC) and proper prediction of its scatter limits in transition region is possible. In particular, it is important to take into account the threshold stress σ_(th) when predicting the lower envelope curve for fracture toughness K_(IC), i.e. the K_(IC) value corresponding to a total probability of 5%.