Influence of threshold parameters on cleavage fracture predictions using the Weibull stress model

This study explores applications of three-parameter Weibull stress models t o predict cleavage fracture behavior in ferritic structural steels tested i n the transition region. The work emphasizes the role of the threshold para meters (sigma (th) and sigma (w-min),) in cleavage fracture predictions of a surface crack specimen loaded predominantly in tension for an A515-70 pre ssure vessel steel. A recently proposed procedure based upon a toughness sc aling methodology using a modified Weibull stress (sigma*(w)) extends the c alibration scheme for the Weibull modulus, in, to include the threshold par ameters. The methodology is applied to calibrate the Weibull stress paramet er for the tested material and then to predict the toughness distribution f or the surface crack specimen. While the functional relationship between oz and in sugests a strong effect of the threshold stress, sigma (th), on the calibrated m-parameter, the results show a remarkably weak dependence of f racture predictions on sigma (th) as does the dependence of fracture predic tions on sigma (w-min) for this specimen.