Code of practice : small punch testing of reference material BCR-661 (Nimonic 75) : open access to JRC Research Infrastructures; 2020-1-RD-EMMA-SMPA, SPT-INVEST

One of the main aims of SPT-INVEST project was to assess the reference material BCR-661 (Nimonic 75) in greater detail with the aim of clarifying, if this reference material (which is according to the ISO 6892, Part 1 standard only for uniaxial tensile testing) would also be suitable for the small punch test (EN-10371). The test results and assessment reported here clearly indicate that for room temperature testing the material shows great potential. However, this report also shows that special attention has to be given to laboratory specific test set-up differences, e.g. puncher, receiving hole and chamfer actual dimensions. For proof strength estimation the chosen methodology for extracting the representative Fe forces has clearly different correlation coefficients and different sensitivity to the test piece thickness. For the tensile strength, estimations by correlation to the classical maximum force (Fm) over the location of the maximum displacement vm or deflection um, also result in uncertainties regarding the optimal correlation constant for the here tested specimen thickness range. This report gives the estimated friction coefficient for the JRC test lab specific test set-up, but suggests that future work still has to be performed in fine-tuning the models used by the finite element software, i.e. a damage model capable of catching the final plastic collapse stage of the SP tests. The here reported correlation coefficients for force to stress conversion still need further fine-tuning based on a larger data base. This is planned to be accomplished through an inter laboratory round-robin. The discussion part of this report includes some recommendations for the future round-robin exercise.