Relationship Between Weibull Parameter and Fracture Toughness of Structural Steels

The brittle fracture assessment for structural components excluding an excessive conservatism should be conducted under the concept of fitness-for-service assessment. One of the factors that lead to such a conservative estimation of brittle fracture performance is no consideration of plastic constraint loss in structural components compared to the fracture toughness test specimen. The Weibull stress criterion is expected to correct the CTOD (Crack Tip Opening Displacement) fracture toughness of materials to the critical CTOD for structural components of concern through the same level of Weibull stress, which take into account not only the difference in plastic constraint but also volume of fracture process zone between toughness test specimen and structural components. On the basis of the Weibull stress criterion, the fracture driving force, that is the Weibull stress, is dependent on the Weibull shape parameter m. Furthermore, such dependency is influenced by both the plastic constraint level and the volume of fracture process zone for specimens of interest. The different m-value would result in the different correction ratio of the fracture toughness to the critical CTOD for structural components. Accordingly, the parameter m should be estimated for the appropriate fracture performance evaluation in consideration of constraint loss correction. In this paper, a simple method for estimating the Weibull shape parameter m were introduced. That is the effort to address the factors to affect the m-value in terms of strength class and toughness level of materials based on the data from literatures, which is for efficient and rational estimation of m-value without any experimental and numerical works.