Material constraint parameters for the assessment of shallow defects in structural components—Part I: Parameter solutions

This Part I paper describes the numerical derivation of a series of material constraint parameters appropriate for the prediction of constraint effects on cleavage fracture toughness in ferritic steels. A series of Lookup Tables and functions are derived which enable parameters to be readily established based on a knowledge of the yield and work hardening behaviour of the material at the temperature of interest and the Beremin cleavage fracture model parameter m. These are provided for use where crack-tip constraint is quantified either in terms of the elastic T-stress normalised by the yield stress or the elastic–plastic Q-stress. Methods for the derivation of these values are described and illustrated with respect to a mild steel plate tested at −50 °C. A comparison of the predicted variation of cleavage fracture toughness with decreasing constraint has been shown to provide a conservative description of the fracture toughness data. The companion Part II paper describes the use of the tables within the context of the R6 defect assessment procedure to assess the behaviour of a cruciform specimen containing a shallow crack under equibiaxial loading.