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The R-curve approach for the fracture assessment of an aluminium alloy bridge. / C.M.S Cheung

Swansea University Author: C.M.S Cheung

Abstract

A result of fatigue testing on a full scale aluminium alloy bridge, which is used by the military for temporary crossings, showed an unexpected increase in fracture resistance, compared with its plane strain K[IC]. This increase was due to a combination of low constraint and large stable crack exten...

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Published: 2001
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42424
first_indexed 2018-08-02T18:54:40Z
last_indexed 2018-08-03T10:10:07Z
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recordtype RisThesis
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spelling 2018-08-02T16:24:29.2130002 v2 42424 2018-08-02 The R-curve approach for the fracture assessment of an aluminium alloy bridge. 64d44fa9657f456e6d9a9d0a9e26897d NULL C.M.S Cheung C.M.S Cheung true true 2018-08-02 A result of fatigue testing on a full scale aluminium alloy bridge, which is used by the military for temporary crossings, showed an unexpected increase in fracture resistance, compared with its plane strain K[IC]. This increase was due to a combination of low constraint and large stable crack extension in the bridge components. Previous work had attributed the increase to the loss of constraint alone, but the present work shows stable cracking is equally important. The effect of stable cracking in the bridge alloy was first examined experimentally in large 25mm thick 3PB specimens which were analysed numerically using the finite element method. The numerical 2-D results provided a concave J[R]-curve showing that dJ[R]/da rises increasingly with crack extension. This increase is associated with the transition from flat to slant fracture in the experimental test pieces, due to the loss of plane strain constraint. Fracture assessment using the R-curve approach showed that long cracks, both in large fracture mechanics specimens and the bridge girder, are stable because, although for a given load, G=J[R], dG/dadJ[R]/da when G=J[R]. The J[R]-curve for low constraint geometries should be indexed by the T-stress. The fatigue crack growth rate for the bridge alloy, taken from different sources, was compared. The Paris law index was nearly 4 for large CT and tension specimens, but only about 2 from fatigue tests on a full-scale bridge. For a large tension specimen, the corresponding K[IC] at the change in index was delayed from 35 (the plane strain K[IC] value) to 48MPa&radic;m, because of the effect of low constraint. A simple model based on the J[R]-curve (at initiation) was developed for predicting crack extension under high cyclic load (K[max]>K[IC]), but with limited success. E-Thesis Civil engineering. 31 12 2001 2001-12-31 COLLEGE NANME Engineering COLLEGE CODE Swansea University Doctoral Ph.D 2018-08-02T16:24:29.2130002 2018-08-02T16:24:29.2130002 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised C.M.S Cheung NULL 1 0042424-02082018162453.pdf 10798132.pdf 2018-08-02T16:24:53.3170000 Output 8792060 application/pdf E-Thesis true 2018-08-02T16:24:53.3170000 false
title The R-curve approach for the fracture assessment of an aluminium alloy bridge.
spellingShingle The R-curve approach for the fracture assessment of an aluminium alloy bridge.
C.M.S Cheung
title_short The R-curve approach for the fracture assessment of an aluminium alloy bridge.
title_full The R-curve approach for the fracture assessment of an aluminium alloy bridge.
title_fullStr The R-curve approach for the fracture assessment of an aluminium alloy bridge.
title_full_unstemmed The R-curve approach for the fracture assessment of an aluminium alloy bridge.
title_sort The R-curve approach for the fracture assessment of an aluminium alloy bridge.
author_id_str_mv 64d44fa9657f456e6d9a9d0a9e26897d
author_id_fullname_str_mv 64d44fa9657f456e6d9a9d0a9e26897d_***_C.M.S Cheung
author C.M.S Cheung
author2 C.M.S Cheung
format E-Thesis
publishDate 2001
institution Swansea University
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Uncategorised{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Uncategorised
document_store_str 1
active_str 0
description A result of fatigue testing on a full scale aluminium alloy bridge, which is used by the military for temporary crossings, showed an unexpected increase in fracture resistance, compared with its plane strain K[IC]. This increase was due to a combination of low constraint and large stable crack extension in the bridge components. Previous work had attributed the increase to the loss of constraint alone, but the present work shows stable cracking is equally important. The effect of stable cracking in the bridge alloy was first examined experimentally in large 25mm thick 3PB specimens which were analysed numerically using the finite element method. The numerical 2-D results provided a concave J[R]-curve showing that dJ[R]/da rises increasingly with crack extension. This increase is associated with the transition from flat to slant fracture in the experimental test pieces, due to the loss of plane strain constraint. Fracture assessment using the R-curve approach showed that long cracks, both in large fracture mechanics specimens and the bridge girder, are stable because, although for a given load, G=J[R], dG/dadJ[R]/da when G=J[R]. The J[R]-curve for low constraint geometries should be indexed by the T-stress. The fatigue crack growth rate for the bridge alloy, taken from different sources, was compared. The Paris law index was nearly 4 for large CT and tension specimens, but only about 2 from fatigue tests on a full-scale bridge. For a large tension specimen, the corresponding K[IC] at the change in index was delayed from 35 (the plane strain K[IC] value) to 48MPa&radic;m, because of the effect of low constraint. A simple model based on the J[R]-curve (at initiation) was developed for predicting crack extension under high cyclic load (K[max]>K[IC]), but with limited success.
published_date 2001-12-31T04:21:31Z
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score 11.08976

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