Abstract
In the boilers of civil nuclear power reactors, stainless steel components are subject to high temperatures and complex, multiaxial, loads. This results in said components being subjected to creep and plastic deformation/damage. Procedures such as R5 and RCC-MRx are utilised to assess the structural integrity of components. These procedures are known to be overly conservative, limiting the lifetime and economic potential of civil nuclear power reactors. Structural integrity procedures utilise a wealth of macroscopic material data to create phenomenological material models. In order to reduce conservatism, mechanistic based models could be utilised.One such approach is the Crystal Plasticity Finite Element (CPFE) method. This approach models deformation behaviour at the mesoscale by explicitly accounting for grain orientation and morphology hence, the volume average stress-strain response is representative of the macroscopic material behaviour. A considerable amount of work has used CPFE modelling to predict uniaxial loading behaviour at the meso- and macro-scale, whereas less has been done to explore CPFE response under multiaxial conditions. Investigating, and subsequently validating, CPFE models under multiaxial conditions will allow for the eventual application at the component-scale and aid in the prediction of creep and plastic deformation/damage, aiding in the removal of unnecessary conservatism from structural integrity procedures.
This thesis validates a multiscale modelling framework under multiaxial creep conditions. Displacements from continuum scale models are utilised as boundary conditions on CPFE models. Initially, specimens were pre-strained and subsequent creep tests performed under uniaxial conditions and simulated to understand the creep-plasticity predictive capabilities of the CPFE model. Following this, the multiscale modelling framework is detailed and validated under uniaxial and biaxial conditions. The final two chapters validate this approach at the inter- and intra-granular scale under multiaxial loading conditions at high and room temperature. This was achieved using neutron diffraction and high resolution digital image correlation.
| Date of Award | 30 Sept 2025 |
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| Original language | English |
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| Supervisor | Christopher E Truman (Supervisor) & Harry Coules (Supervisor) |