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Microstructural Characterisation of Structural Bolt Assemblies in Fire

Johnson, Lucy (2014) Microstructural Characterisation of Structural Bolt Assemblies in Fire. PhD thesis, University of Sheffield.

Microstructural Characterisation of Structural Bolt Assemblies in Fire.pdf
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In structural fire engineering, the importance of bolt assemblies is often overlooked. Connection design uses the temperature-dependent bolt strength-reduction factors prescribed in Eurocode 3, despite the existence of two distinct failure modes under tension; bolt breakage, and thread-stripping. This thesis investigates the factors which influence failure modes at ambient and elevated temperatures and a range of strain-rates through microstructural characterisation, tensile testing and finite element modelling. Microstructural characterisation carried out on M20 galvanised bolt assemblies consisting of Grade 8.8 bolts and Property Class 10 nuts from a range of manufacturers has highlighted that, despite a specified tempered-martensite microstructure, microstructural variations existed between different manufacturers and within a single batch. These microstructural variations not only affected the flow behaviour of the bolt material but determined the failure modes of bolt assemblies at ambient temperatures. Tensile testing of turned-down bolts allowed the temperature and strain-rate dependent flow behaviour of bolt material to be investigated, eliminating the effect of thread deformation. The flow curves obtained were input to a finite element model to represent true bolt material behaviour, which was validated against force-displacement curves obtained from uniaxial tensile testing of bolt assemblies from the same batch. Both experimental and finite element modelling work have highlighted the importance of using a tight thread tolerance class combination and a suitably tall nut to ensure ductile bolt breakage failures and avoid thread-stripping.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.634328
Depositing User: Miss Lucy Johnson
Date Deposited: 29 Jan 2015 15:51
Last Modified: 03 Oct 2016 12:09
URI: http://etheses.whiterose.ac.uk/id/eprint/7730

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