Numerical investigations on size effects and mini-CT applications for Master Curve determination

This paper presents a comprehensive numerical study on size effects and the application of mini-compact tension (mini-CT, or MCT) specimens within the Master Curve methodology for determining fracture toughness, particularly in irradiated nuclear materials. This study, conducted as part of the FRACTESUS project, involves collaboration among several European laboratories to estimate the efficacy of mini-CT specimens through extensive finite element modelling (FEM) and inter-laboratory simulations. The research addresses critical factors, including the consistency of FEM codes, the impact of crack length on displacement conversion factors, and the application of the Beremin model for brittle fracture analysis. The good consistency between the results obtained by the different laboratories validates the numerical approach. The comparison of the macroscopic and local mechanical fields between 1T-CT and MCT specimens highlights the in- and out-plane loss of constraint and the deterioration in the plane strain state in MCT, resulting in the apparent fracture toughness shift on the measured $T_0$ value. The numerical analysis of this shift using the Beremin model show that: (i) numerical simulations can accurately replicate experimental results obtained with MCT specimens, (ii) a size effect is observed on the Beremin fracture parameters, (iii) the use of cross-parameter sets between geometries does not yield satisfactory results, and (iv) the $T_0$ value, using the same parameters for both specimen geometries, is lower is the MCT compared to 1T-CT suggesting that MCT can lead to non-conservative results with respect to 1T-CT.