Finite Element Modelling of the Small Punch Test for Structure Critical Design

The development of nuclear fusion reactors presents complex challenges in materials design and development. To ensure that structure critical materials can withstand the conditions within the pressure vessel extensive testing must be carried out. This will include, in part, the testing of specially irradiated specimens. The intensity of the irradiation means that only a small volume of material will be produced and available for testing. Necessitating the development of small scale mechanical testing. One such test method is small punch testing. For small punch testing to be considered a viable testing technique for structure critical design a reliable correlation between small scale and bulk scale must be made.
In this thesis the creation of a small punch test finite element model was presented. The model, created in Abaqus 2017, was used as a basis for the optimisation of Johnson-Cook materials and damage model parameters of P91 and Eurofer97 steels at room temperature. An effective method for the optimisation of the Johnson-Cook materials model parameters was developed. This method utilised the scripting capabilities of Abaqus in conjunction with the SciPy optimise module within Python to perform inverse analysis via the Nelder-Mead algorithm. The results were successfully validated by use of the Considére Criterion, demonstrating that they were conservative with a confidence of 95%. The early stages of a method for the optimisation of the Johnson-Cook damage model parameters were presented, with the effects of the friction between sample and punch head was also highlighted.
The force-deflection curve analysis methodologies provided in the code of best practice and ASTM standard were also analysed. Examination of the proof stress and UTS estimation methods provided in the code of best practice methods displayed an overestimation when calculating values from steel tests at room temperature.
Overall, the basis for the development of a novel method for the calculation of Johnson-Cook materials and damage behaviour from a small punch test was presented. Through effective validation this, and further work has the potential to be applied in the design and quality assurance of structural materials for future fusion reactors.