Use of a Unified Model for the Fracture Toughness of Ferritic Steels in the Transition and on the Upper Shelf in Fitness-for-Service Assessment and in the Design of Fracture Toughness Experiments

Abstract

Models to predict the fracture and arrest behavior of ferritic steels have long been under development. The current, most widely accepted model of fracture toughness behavior is the ASTM E1921-02 “Master Curve” that is used to predict the variation of the median cleavage fracture toughness (KJc) with temperature in the transition temperature region, as well as predicting the scatter of data about the median at any given temperature. Recently, models describing the variation of crack arrest fracture toughness (KIa) and of ductile initiation fracture toughness (JIc) with temperature have also been proposed. Moreover, models are also available that relate these various temperature dependencies to each other, and relate them all a common parameter, the cleavage crack initiation fracture toughness index temperature To. Research work continues to better quantify these relationships and to more firmly understand their physical bases. Nevertheless, the ample empirical evidence on which the models are based and the existing physical understanding underlying the models suggests that they can be used as a tool in both fitness-for-service assessment and in the design of experiments conducted to investigate the fracture toughness of ferritic materials. While still being developed, these toughness-based models offer clear advantages relative to alternative (correlative) approaches in terms of reduced prediction uncertainty. In this paper we amalgamate the results of previous publications to provide an algebraic expression for the variation of KJc, KIa, and JIc with temperature that includes explicit quantification of the uncertainty in each variable. We also discuss the implications and potential applications of this combined model.