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

Paper Number: 124294

124294 - Modelling the Effect of Residual Stresses on Damage Accumulation Using a Coupled Crystal Plasticity Phase Field Fracture Approach 

Nuclear reactor components can be subjected to a range of complex loading conditions consisting of temperatures of more than 300 degrees Celsius, stresses of more than 200MPa, and irradiating neutrons for prolonged periods of time. Under these conditions, a range of degradation mechanisms are of interest including creep, plasticity, and eventual ductile failure.

Understanding how austenitic stainless steels such as 316H used to produce these components degrade when subjected to these conditions is a key design focus for lifetime assessment and extension. Microstructural features such as grain morphology, texture, and the presence of second phases and precipitates are thought to have a having a strong influence on how damage can initiate and degrade material performance. These factors can then be exacerbated by the presence of residual stresses from prior loading, manufacturing processes, and welding. Of particular interest are type 1 residual stresses, which are macroscopic stresses present across multiple grains of the material after the initial load has been removed.

This work includes a dislocation-based crystal plasticity finite element (CPFE) modelling framework to FCC 316H austenitic stainless-steel microstructures with a coupled energy-based phase field fracture model. The coupling of both damage and plasticity allows for modelling of real time degradation in material performance. The type 1 residual stress field was determined through simulating an initial loading stage through the implementation of displacement boundary conditions, before the boundary conditions are relaxed. Upon subsequent loading, the phase field fracture model was used to determine the level of accumulated damage and the rate of damage accumulation under different loading conditions both in presence and absence of the determined residual stress field.

Two types of microstructures have been considered within this work. Firstly, a direct microstructural reconstruction within crystal plasticity of 316H stainless steel found using an electron backscatter diffraction measurement, producing a planar mesh of columnar elements was implemented. Secondly, an artificial microstructure of a weld region generated from a phase field grain growth model of 316H was used, allowing for a comparison in damage evolution when loading is in line with or across the weld direction.

This procedure and modelling framework allows for a comparison of damage accumulation depending on loading direction, texture, microstructure, and the presence of type 1 residual stresses.

Presenting Author: Michael Salvini University of Bristol

Presenting Author Biography: Michael Salvini is a PhD student studying at the University of Bristol in the School of Electrical, Electronic and Mechanical Engineering. His research focuses on the use of finite element modelling techniques such as crystal plasticity combined with damage modelling approaches such as phase field fracture to understand the microstructural features that can affect both early damage initiation and final material failure in steels. The primary focus is applications towards civil nuclear energy, with irradiation, plasticity, and creep of key interest in ferritic and ferritic martensitic steels for reactor pressure vessels, and austenitic stainless steels used boiler head components. These modelling techniques are used in tandem with experimental techniques such as EBSD, HR-DIC, SEM, and tensile testing to validate modelling approaches.

Authors:

Michael Salvini University of Bristol
Nicolò Grilli University of Bristol
David Knowles Henry Royce Institute
Mahmoud Mostafavi University of Bristol
Parsa Esmati University of Bristol
Maria S. Yankova University of Manchester
Thomas F. Flint University of Manchester
Mike C. Smith University of Manchester
Anastasia N. Vasileiou University of Manchester
Nicolas O. Larrosa Tecnalia
Christopher Truman University of Bristol