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An investigation of the use of metal matrix composites for pressure vessels.

Watt, Gerald (2018) An investigation of the use of metal matrix composites for pressure vessels. Doctoral thesis, University of Surrey.

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Continuous reinforcement metal matrix composites (MMCs) have yet to become widely used within the aerospace industry. Despite the high stiffness and strength of unidirectional MMCs, the complexity and inherent cost of manufacture are major factors that have prevented the widespread uptake of these advanced materials. Furthermore, the relatively poor mechanical performance of unidirectional MMCs subjected to transverse loads has largely precluded their use in structures which experience complex loading (with the notable exception of bladed compressor discs in gas turbines). Recently, TISICS has been involved in projects with two major aerospace companies to investigate the use of titanium and aluminium matrix composites. In both projects it was necessary to examine the properties of less conventional cross-ply composites and the work undertaken by the author in conjunction with these projects forms the basis of this EngD thesis. A range of MMC layups were tested in tension, compression and shear and detailed microscopy was undertaken to investigate the failure processes. A simple rule-of-mixtures approach was found to show good agreement with the unidirectional tensile test results. Subsequently, a more complex approach taking ‘weighted’ averages for biaxial and multiaxial laminates at a ply level was developed and this enabled full tensile response of the composites to be modelled, albeit with some limitations in low strain response. Part of the work which was conducted to increase the understanding of cross-ply composites involved the determination of residual stresses. Although cross-ply MMCs were thought to have greater axial residual stresses than unidirectional MMCs, the variation of residual stresses throughout the eight ply laminates was found to change significantly (from 0.37% in the innermost to 0.23% in the outermost plies) depending on the sub-laminate sequence. Finite element modelling predictions were compared to the experimental residual stress determination techniques and it was found that the FE modelling underestimated the strains in cross-ply composites. Both aluminium and titanium pressure vessels were manufactured and tested; the mechanical data from pressurisation was compared to simple analytical modelling and macroscale FEA. Metallographic samples studied from the failed vessels showed deficiencies in manufacture and a rudimentary form of acoustic emission showed that damage was incurred at relatively low strains, but did not propagate to failure during the proof test cycles. This suggests that with adequate provisions, the development of damage within a cross-ply layup does not need to rule out its use in a non-critical tank application.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Watt, Gerald
Date : 28 February 2018
Funders : EPSRC
Grant Title : The Centre for Doctoral Training in Micro- and NanoMaterials and Technologies (MiNMaT)
Copyright Disclaimer : ©2017 Copyright of this document is held by TISICS Ltd and the University of Surrey. All rights reserved. No part of this document may be reproduced without written consent of the owner(s).
Contributors :
Depositing User : Gerald Watt
Date Deposited : 05 Mar 2018 09:38
Last Modified : 28 Feb 2020 02:08

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