Computational framework for fracture of graphite bricks in an AGR core

Kodsi, Costy (2017) Computational framework for fracture of graphite bricks in an AGR core. PhD thesis, University of Glasgow.

Abstract

Life-extension of EDF Energy's existing nuclear fleet is based on an assumption of continued safe operation. Potential fracture of graphite bricks in the nuclear reactor core of a power station represents an unknown variable in the equation. An understanding of the nature of this phenomenon and the impact on operation of the power station is desired. This work prepares the way for the future study of fracture in graphite bricks in a reactor core subject to dynamic excitation. Methodology to couple a multi-body finite element contact code to a crack propagation code is thus developed. Three important scientific contributions have been made:

(i) An optimisation problem formulated on a smooth manifold to yield the rotation responsible for infinitesimal rigid body motion. This involves an iterative scheme in the form of Newton's method that takes into account the geometry of the underlying parameter space. There are no issues with singularities or additional computations in each iteration to scale the solution onto the manifold.

(ii) An energy consistent crack initiation criterion for brittle material where nucleation is treated as a sudden and discrete rupture event at the macroscopic level. At the heart of the criterion is the finite difference form of the energy release rate; an expression for the characteristic length is derived and the change in total potential energy is obtained from an asymptotic argument involving the topological derivative. The criterion can predict crack onset at a sharp or blunt notch. Fracture toughness and material strength are the only input requirements.

(iii) Algorithms related to the detection of sharp notches in a tetrahedral finite element mesh and a general computational procedure for evaluation of non-local crack initiation criteria. The only tool in the implementation of these algorithms is C++11. There is no need for a complex data structure storing all incidence information. Unordered associative containers in the standard library are exploited in the design of these rather efficient algorithms, which cover surface extraction and provide connectivity of the edges representing a sharp notch tip. A mesh re-generation routine for purposes of refinement at the sharp notch tips has also been developed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Infinitesimal rigid body motion mitigation, crack initiation criterion, automatic sharp notch tip detection, non-local criteria evaluation procedure.
• Subjects: Q Science > QA Mathematics; Q Science > QC Physics; T Technology > TA Engineering (General). Civil engineering (General); T Technology > TJ Mechanical engineering and machinery
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: Engineering & Physical Sciences Research Council (EPSRC), Engineering & Physical Sciences Research Council (EPSRC), Engineering & Physical Sciences Research Council (EPSRC), Engineering & Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Pearce, Prof. Chris J.
• Date of Award: 2017
• Depositing User: Costy Kodsi
• Unique ID: glathesis:2017-8084
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 07 Apr 2017 09:11
• Last Modified: 31 May 2017 07:39
• URI: https://theses.gla.ac.uk/id/eprint/8084