Fracture toughness test is an important method to monitor critical facilities' structural integrity and service life. Due to the limited storage space for test materials, these facilities may not provide sufficient specimens. Using sub-size specimen is one way to solve this problem. However, the resulting constraint loss often leads to errors in the measured fracture toughness. In terms of quantifying and correcting such deviations, a current research hotspot is the toughness scaling model (TSM for short) based on the Beremin model. This paper will apply the latest modified Beremin model to this TSM to study the scaled fracture toughness probability distribution. In the article, a new parameter calibration method is proposed to reduce the uncertainty of parameters used in the TSM. After that, the TSM based on the modified Beremin model is used to scale the fracture toughness of the sub-size specimens and compared with the standard specimens. The results show that the TSM still cannot accurately scale the entire J-integral probability distribution of small specimens. It is also found that the parameter a, which describes the J-integral distribution of the specimens, has a noticeable influence on the scaled fracture toughness, and this influence can be used to reduce the deviation of the scaled fracture toughness.

The standard fracture toughness test is usually limited in practical engineering projects due to the expensive and sophisticated experimental procedure or limited specimens. The traditional method to evaluate the structural integrity is to estimate the ductile-brittle transition region by Charpy tests. However, this fuzzy estimation is sometimes too conservative and cannot obtain quantitative fracture toughness data. In recent years, many achievements have been made in the study of the relations between Charpy impact test and fracture toughness test. Although acceptable, the errors caused by these formulas are rarely compared in detail formulas with stable deviation will be more suitable for research or engineering application. Therefore, this paper compares the data of four different ferritic steels to test the error stability of each formula, so as to provide reference for experimental research and engineering facilities. The reliability of each correlation is checked from the view of accuracy or appropriate conservatism. In this research, We found that the T 28J-T 0 correlations, the empirical formula proposed by Rolfe, Novak and Barsom (abbreviated as RNB) and the Mean-4 Procedure obtained by IGC-parameter give the reference temperatures more accurately or appropriately conservatively. These formulas should be preferred in practical application.

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