Effect of Plastic Constraint on Brittle Fracture in Steel: Evaluation Using a Toughness Scaling Model

Over the past two decades, plastic constraint effects have been an issue of concern in both fracture mechanics and structural integrity research, and several methods have been proposed for considering loss of plastic constraint. This paper shows the ability of a simplified model to predict brittle fracture under low plastic constraint conditions. Fracture toughness tests are performed on single-edge notched bend (SENB) steel specimens with deep and shallow notches, as well as on double-edge notched tension and center-notched tension (CNT) specimens. When compared with SENB specimens with a deep notch, the CNT specimens show high fracture toughness as a result of the loss of plastic constraint at the crack tip. Here, the Weibull stress approach and a toughness scaling model (TSM) are used to consider the effects of the loss of plastic constraint on the fracture toughness of the specimens. The corrected fracture toughness values evaluated by the TSM are found to be close to the toughness values observed in the tests and to the values predicted by the Weibull stress approach. This paper also briefly discusses the effect of ductile crack growth on brittle fracture.