Fracture mechanics-based defect assessment procedures assume flaws are infinitely sharp cracks. However, this results hi large safety factors for non-sharp flaws because of the loss of the plastic constraint. Fracture toughness tests were performed on four types of single edge notched bend steel, specimens with different degrees of plastic constraint, caused by fatigue cracks and machined notches with different notch root radii as well as by deep and shallow notches. This paper examines the differences in the stress states of the fatigue cracks and machined notches and the ability of the Weibull stress approach to predict the occurrence of brittle fractures under high and low plastic constraints in a unified manner. (C) 2016 Elsevier Ltd. All rights reserved.