An engineering approach to assess constraint effects on cleavage fracture toughness

This study presents a simplified approach to parameterize constraint effects on the fracture toughness of ferritic steels in the ductile-to-brittle transition (DBT) region under plane strain, small-scale yielding conditions for non-zero T-stress. The Weibull stress serves to couple near tip and global loading which enables scaling of macroscopic toughness values across varying constraint levels. Extensive finite element analyses then provide the relationship of T vs. T/σ0, where T=KJcT≠0/KJcT=0, in closed form for four typical ferritic steels. Given the non-dimensional T-function for a material, the scaling of fracture toughness values for constraint loss involves only simple function evaluations, making the method suitable for use in more global simulations of fracture events, e.g. parametric studies to exam a wide range of crack sizes, locations and loadings. The paper describes several possible applications of the T-function model to correct toughness data for constraint loss, including shifts of the DBT reference temperature, T0, for the material determined according to ASTM E-1921. Comparisons of model predictions of ΔT0 are made with those determined from measured toughness data for an A515-70 steel.