Crystal plasticity finite element models can simulate the effect of microstructure on the cyclic behaviour of polycrystalline steels and can simulate the resulting local plastic strain. However, such models are computationally expensive and are therefore limited to simulation on small volume elements of material. In this work, a Gaussian process regression model is proposed as a surrogate model to predict macroscopic quantities of interest based on input parameters relating to the cyclic loading and material microstructure. The advantage with relation to computational expense of the surrogate can be leveraged for the purposes of undertaking uncertainty quantification and sensitivity analysis regarding the effect of the model inputs on the output prediction.
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Themes: Mechanical Behavior in Nuclear Materials
IN SITU X-RAY TOMOGRAPHY IMAGING OF CRACK INITATION AND PROPAGATION IN NUCLEAR GRAPHITE AT 1000°C [Keynote]
Nuclear-grade graphite is a critically important high-temperature structural material for current and potentially next generation of fission reactors worldwide. It is imperative to understand its damage-tolerant behaviour and to discern the mechanisms of damage evolution under in-service conditions. Here we perform in situ mechanical testing with synchrotron X-ray computed micro-tomography at temperatures between ambient and 1,000 °C on a nuclear-grade Gilsocarbon graphite. We find that both the strength and fracture toughness of this graphite are improved at elevated temperature. Whereas this behaviour is consistent with observations of the closure of microcracks formed parallel to the covalent-sp2-bonded graphene layers at higher temperatures, which accommodate the more than tenfold larger thermal expansion perpendicular to these layers, we attribute the elevation in strength and toughness primarily to changes in the residual stress state at 800–1,000 °C, specifically to the reduction in significant levels of residual tensile stresses in the graphite that are ‘frozen-in’ following processing. A range of other nuclear grade graphite materials were tested and compared with Gilsocarbon graphite.
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