In order to establish a guideline for fracture evaluation without excessive conservatism by considering plastic constraint in the ductile-brittle transition temperature (DBTT) region, the CAF (Constraint-Based Assessment of Fracture in Ductile-Brittle Transition Temperature Region) subcommittee has been launched in 2018 in the Atomic Energy Research Committee of the Japan Welding Engineering Society with a five years’ term. In the committee, fracture tests are conducted using laboratory specimens of C(T), SE(B), and 50mm-thick flat plate with a surface flaw subjected to bending load or tensile load to verify fracture evaluation methods, which strongly depend on numerical simulation. Since simulation results are easily affected by analysis conditions, benchmark analysis is essential for the potential users of the guideline. Therefore, benchmark analyses are executed on brittle and ductile damages by Beremin and Gurson–Tvergaard–Needleman (GTN) models implemented in the FE codes owned by the committee members. The benchmark analyses are carried out in four steps; Step 0 is to confirm the output of finite element (FE) codes in each member with the same input data and the same FE model. Step 1 is to confirm the result of Weibull stress analysis for C(T) specimens tested at −125°C. The Weibull parameter, m, was fixed in this step. At step 2, sensitivity analyses are conducted on Weibull stresses in different conditions. The outputs by the GTN model are also confirmed. At the final step, the fracture simulation will be run for flat plate specimens with less plastic constraint than the standard fracture toughness specimen. As the results of the benchmark analyses up to step 2, a significant difference are not observed in the Weibull stress computed by committee members with the same input data and FE model and it is confirmed that the effects of element type, nonlinear deformation theory employed in FE analysis and convergence procedure for the Weibull parameter m are marginal by the sensitivity analyses. For the calculation of the Weibull parameter m by using the fracture toughness test results and the developed programs by committee members, the converged values of m show good agreement among them. The obtained knowledge by the benchmark analyses is used to establish the guideline for fracture assessment of structural components with different plastic constraints.

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