Towards the Standardization of Small Specimen Test Techniques For Fusion Applications

Small Specimen Testing Techniques and accepted guidelines are indispensable for generating valid material data bases for next step fusion plants engineering and commissioning.
SSTT standardization mandatory vs essential:
To obtain approvals for fusion material testing and generation of valid mechanical data using SSTT, standardization accepted by an international organization is strictly speaking not “mandatory”, but an essential step to ease and smoothen the upcoming processes. To break it down: the use of an international code framework (RCC or ASME) is essential. To have fusion materials “nuclear code qualified” as a material annex to codes is essential. In the course of approving (material) data, tests following standards are essential. A “recent” experience was the acceptance of EUROFER as material Annex [A3.19AS and A9.J19AS] to RCC-MRx. This paves the way to conformity analyses to get an approval for EU TBM (test blankets modules) in ITER operation in front of some notified body. The approval process with AFCEN has been very tedious, difficult and time consuming. As some tests that contribute to EUROFER data base are not gathered under agreed standards (standard specimen size), the validity of results had to be proven on a case by case basis. Therefore, to generate SSTT accepted guidelines as a step towards any kind of standard(ization) shall be considered as a huge progress in the fusion technology community.
The Round Robin exercise
The Round Robin (RR) tests shall make a solid case: through-out all test matrices on five different test techniques it is performed with a minimum of two reference materials, reducing the risk to become trapped with some specificity of one material. F82H and EUROFER, in particular, have been developed over more than two decades and are widely characterized in non-irradiated state. The benefit of the material selection is not only that already comprehensive data bases exist (each, partly gained on standard and small specimen), but as well that they are the reference materials for ITER TBM and strong candidates for DEMO, respectively in Japan and EU. Other quality features of the RR test include the number of independent participating institutes and organisations, the internationality (Japan, US, China; Germany, Spain, UK), their over decades developed experience as well as the density of the test matrices, where a minimum of two and up to 6 participants contribute to the individual test techniques.
The tensile test as example:
Tensile testing is specific: it provides multiple values (strength, ductility measures and the true stress vs. true strain curve) that are needed for the bulk of design criteria that rule “monotonic loading” in structural analyses. Data from tensile tests as well serve as input to evaluation methodologies of other test techniques such as the Weibull stress analysis in fracture toughness (part of “local approach” and applied in this CRP as well).
The Round Robin experiments planned in this CRP will provide statistical data, e.g., bias and precision, of the miniature tensile test technique. In short, preparatory assessment in this CRP support to judge reliability (i.e., repeatability and reproducibility) of the generated data. This is an essential part in standardization of SSTT by ASTM or other regulatory authorities. In view of next steps, the draft guidelines proposed in this CRP lean on existing standards such as ASTM.
The developmental of non-contact strain measurement technique proposed and applied in the RR definitely shall become a common and general tool well beyond the fusion community and shall have application in a wide range in industrial fields.