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Finite Element Modelling of Fracture and Damage in Austenitic Stainless Steel in Nuclear Power Plant

Arun, Sutham

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

The level of residual stresses in welded components is known to have a significant influence on their failure behaviour. It is, therefore, necessary to understand the combined effect of mechanical loading and residual stresses on the ductile fracture behaviour of these structures in order to provide the accurate structural safety assessment. Recently, STYLE (Structural integrity for lifetime management-non-RPV component) performed a large scale bending test on a welded steel pipe containing a circumferential through-thickness crack (the MU2 test). The purpose of this test is to study the impact of high magnitude weld residual stresses on the initiation and growth of cracks in austenitic stainless steels.This research presents the simulation part of the STYLE project which aims to develop the finite element model of MU2 test in ABAQUS to enhance the understanding and ability to predict the combined influence of mechanical loading and residual stresses on the ductile fracture behaviour of nuclear pressure vessel steels. This research employs both fracture mechanics principles (global approach) and Rousselier damage model (local approach) to study this behaviour including crack initiation and growth. In this research, the Rousselier model was implemented into ABAQUS via the user defined subroutines for ABAQUS/Standard and ABAQUS/Explicit modules, i.e. UMAT and VUMAT. The subroutines were developed based on the integration algorithm proposed by Aravas and Zhang. The validation of these subroutines was checked by comparing the FE results obtained from the implementation of these subroutines with the analytical and other benchmark solutions. This process showed that UMAT and VUMAT provide accurate results. However, the UMAT developed in this work shows convergence problems when the elements start to fail. Hence, only VUMAT was used in the construction of the finite element model of the MU2 test. As mentioned above, the results obtained from both fracture mechanics approach and Rousselier model are compared with the experimental data to validate the accuracy of the model. The results shows that both fracture mechanics approach and the Rousselier model predict similar final crack shapes which correspond closely to the test results in south direction. The other conclusions about the influence of residual stress on ductile fracture obtained from this work are also summarized in this thesis.

Layman's Abstract

Welded structures in a power station endure operational loads together with residual stresses introduced during manufacture and repair. It is, therefore, necessary to understand the combined effect of mechanical loading and residual stresses on the ductile fracture behaviour of these structures in order to provide an accurate structural integrity assessment. Recently, STYLE (Structural integrity for lifetime management-non-RPV component) performed a large scale bending test on a welded steel pipe containing a circumferential through-thickness crack (the MU2 test). The data obtained from the tests was used to support the FE models developed in this research to study the impact of high magnitude repair-weld residual stresses on ductile crack initiation and growth.In this research, a three-dimensional FE model of MU2 test was developed using ABAQUS. The weld residual stress field was introduced into the FE model as initial stresses using an iterative method. The parameters of conventional fracture mechanics (global approach) and Rousselier damage model (local approach) were employed to study the combined influence of primary and residual stresses on ductile fracture behaviour including crack initiation and growth. The main contributions from this research can be summarized this research.

Bibliographic metadata

Type of resource:
Content type:
Administered thesis
Form of thesis:
Traditional
Type of submission:
Doctoral level ETD - final
Thesis title:
Finite Element Modelling of Fracture and Damage in Austenitic Stainless Steel in Nuclear Power Plant
Degree type:
Doctor of Philosophy
Degree programme:
PhD Mechanical Engineering
Publication date:
2015-07-11T12:27:44
Institution:
The University of Manchester
Location:
Manchester, UK
Total pages:
203
Abstract:
The level of residual stresses in welded components is known to have a significant influence on their failure behaviour. It is, therefore, necessary to understand the combined effect of mechanical loading and residual stresses on the ductile fracture behaviour of these structures in order to provide the accurate structural safety assessment. Recently, STYLE (Structural integrity for lifetime management-non-RPV component) performed a large scale bending test on a welded steel pipe containing a circumferential through-thickness crack (the MU2 test). The purpose of this test is to study the impact of high magnitude weld residual stresses on the initiation and growth of cracks in austenitic stainless steels.This research presents the simulation part of the STYLE project which aims to develop the finite element model of MU2 test in ABAQUS to enhance the understanding and ability to predict the combined influence of mechanical loading and residual stresses on the ductile fracture behaviour of nuclear pressure vessel steels. This research employs both fracture mechanics principles (global approach) and Rousselier damage model (local approach) to study this behaviour including crack initiation and growth. In this research, the Rousselier model was implemented into ABAQUS via the user defined subroutines for ABAQUS/Standard and ABAQUS/Explicit modules, i.e. UMAT and VUMAT. The subroutines were developed based on the integration algorithm proposed by Aravas and Zhang. The validation of these subroutines was checked by comparing the FE results obtained from the implementation of these subroutines with the analytical and other benchmark solutions. This process showed that UMAT and VUMAT provide accurate results. However, the UMAT developed in this work shows convergence problems when the elements start to fail. Hence, only VUMAT was used in the construction of the finite element model of the MU2 test. As mentioned above, the results obtained from both fracture mechanics approach and Rousselier model are compared with the experimental data to validate the accuracy of the model. The results shows that both fracture mechanics approach and the Rousselier model predict similar final crack shapes which correspond closely to the test results in south direction. The other conclusions about the influence of residual stress on ductile fracture obtained from this work are also summarized in this thesis.
Layman's abstract:
Welded structures in a power station endure operational loads together with residual stresses introduced during manufacture and repair. It is, therefore, necessary to understand the combined effect of mechanical loading and residual stresses on the ductile fracture behaviour of these structures in order to provide an accurate structural integrity assessment. Recently, STYLE (Structural integrity for lifetime management-non-RPV component) performed a large scale bending test on a welded steel pipe containing a circumferential through-thickness crack (the MU2 test). The data obtained from the tests was used to support the FE models developed in this research to study the impact of high magnitude repair-weld residual stresses on ductile crack initiation and growth.In this research, a three-dimensional FE model of MU2 test was developed using ABAQUS. The weld residual stress field was introduced into the FE model as initial stresses using an iterative method. The parameters of conventional fracture mechanics (global approach) and Rousselier damage model (local approach) were employed to study the combined influence of primary and residual stresses on ductile fracture behaviour including crack initiation and growth. The main contributions from this research can be summarized this research.
Keyword(s):
Thesis main supervisor(s):
Funder(s):
Degree grantor:
Language:
en

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:268276
Created by:
Arun, Sutham
Created:
11th July, 2015, 11:27:45
Last modified by:
Arun, Sutham
Last modified:
16th October, 2017, 14:10:03

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