Statistical evaluation of fracture toughness with stable crack extension

Abstract

The scatter of fracture toughness in the ductile-brittle transition temperature region was experimentally examined on 500MPa class low carbon steel. The Weibull distribution of the fracture toughness K(Jc) at −60°C showed the single modal distribution with the shape parameter of around 4. The Weibull distributions of the K(Jc and Ju)s at −20°C and −10°C, however, showed the bilinear distributions with the elbow point. The Weibull slopes below the elbow points were closed to the value of 4, but the slopes showed the transition to be smaller above the elbow points. The bilinear Weibull distributions were discussed from the viewpoints of the constraint loss and the stable crack extension. However, the fracture surface observations revealed that the stable crack extension was the main factor that brought the bilinear Weibull distributions. The bilinear Weibull distributions could be qualitatively simulated by the analytical model with the consideration of the stable crack extension.