Session: MF-09-01 Mechanistic Modelling of Deformation and Fracture-1

Paper Number: 122509

122509 - Continuum and Crystal Plasticity Coupled Finite Element Modelling to Explore Complex Loading Conditions 

In civil nuclear power plants, components are exposed to complex thermo-mechanical loading which can lead to damage and subsequent failure of said component. One aspect of structural integrity analysis for these components is macroscopic finite element analysis (FEA). Conventionally, elastic-plastic isotropic/kinematic material models are used in combination with creep deformation laws, such as the RCC-MR creep deformation equations.  

Although this approach has a longstanding pedigree, it is empirically based and fails to simulate more complex loading conditions. Therefore, there has been a shift to more mechanistic approaches – such as crystal plasticity finite element (CPFE) analysis. CPFE attempts to model deformation at the mesoscale by incorporating the underlying material physics. In typical CPFE simulations, periodic boundary conditions are used. These conditions are not reflective of the boundary conditions enforced at the component length-scale. This leads to an inability to apply more complex, multiaxial, loading conditions to CPFE models. 

A multiscale approach has been developed at the University of Bristol which combines macroscopic, empirically based, models and CPFE models. The (macroscopic) component is simulated and resulting displacement conditions at any region within the component are interpolated and enforced as boundary conditions on a CPFE model. This allows CPFE simulations to be performed under more realistic loading conditions. This can then be used to look at the microstructural and macroscopic (RVE averaged) deformation response. 

This methodology has been compared with grain family elastic strain responses. These results were collect via synchrotron neutron and X-ray diffraction at ISIS Neutron and Muon Source and Diamond Light Source. Smooth and notched bars of 316H austenitic stainless steel were loaded at 550°C and subsequently held in displacement-control dwells to invoke stress relaxation. Comparison with this data allows validation of this modelling scheme and hence exploration of more complex boundary conditions.     

Presenting Author: Christopher Allen University of Bristol

Presenting Author Biography: Chris is a PhD student in the Solid Mechanics Research Group (SMRG) at the University of Bristol. He completed his masters degree in nuclear reactor technology in 2020 and subsequently joined the SMRG to research creep and plasticity in high temperature reactor materials. His research aims to improve structural integrity assessment in order to aid the lifetime extension programme of civil AGRs operated by EDF Energy.

Authors:

Christopher Allen University of Bristol
Harry Coules University of Bristol
Christopher Truman University of Bristol