Application of mini-flat and cylindrical test specimens to extract hardening law and ductility of neutron irradiated Eurofer97

Tensile properties such as strength and ductility are essential for structural integrity assessment of critical components. In the context of nuclear applications, the flat tensile geometry as compared to the reference standard cylindrical geometry offers a number of advantages in terms of material use efficiency, ease of machining, best packing under irradiation and simplified remote handling of active samples. Accordingly, the interchangeability of data extracted from flat and cylindrical specimens is a key issue. Furthermore, this interchangeability must be demonstrated for irradiated samples. Many metallic materials show significant reduction or even a full lack of uniform elongation after neutron irradiation, with most of the strain hardening regime taking place during the post-necking stage. As the necking development depends on geometry, this raises questions on the validity of changing the test specimen geometry. Here, the interchangeability of mini-flat and cylindrical tensile samples after neutron irradiation is investigated by combining experimental and computational analysis. The investigated material is EUROFER97 steel irradiated at 300 °C in the conditions relevant for the ITER fusion reactor. Finite element (FE) simulations are performed with a Gurson-type ductile fracture model parameterized based on the experimental tensile response. The hardening law extracted from mini-flat samples and applied to predict the stress-strain response of a cylindrical sample with 90 % accuracy or better in terms of total elongation, reduction of area, and fracture strength as compared to the direct experimental data obtained with cylindrical tensile specimen geometry.