Application of J-Q theory to the local approach statistical model of cleavage fracture

A statistical model has been established to predict the fracture toughness in the lower-shelf and lower transition regions. It considers the in-plane constraint effect in terms of the two-parameter J-Q stress field. This model has been applied to predict the effect of crack depth and specimen geometry on fracture toughness and there is good agreement with experimental data. The specimens with lower in-plane constraints have a large toughness scatter due to the significant constraint loss during the loading process. The lower-bound toughness is not sensitive to crack depth and specimen geometry and this is attributed to the fact that all specimens have a similar in-plane constraint at small loads.