University of Surrey

Test tubes in the lab Research in the ATI Dance Research

The use of digital image correlation to monitor delaminations in composite structures.

Ajmal, Osman Z. (2018) The use of digital image correlation to monitor delaminations in composite structures. Doctoral thesis, University of Surrey.

[img]
Preview
Text
Ajmal Thesis - post Viva correction.pdf - Version of Record
Available under License Creative Commons Attribution Non-commercial Share Alike.

Download (14MB) | Preview

Abstract

The range of applications for composite materials is growing, but understanding of the effect of defects is limited, as is the ability to detect them. Versatile non-destructive testing (NDT) techniques, that can be deployed rapidly and reliably, to detect and monitor damage in composite components are vital to the continued growth of this sector. This research investigates the application of Digital Image Correlation (DIC) as an NDT technique for monitoring delamination defects in Fibre Reinforced Polymer (FRP) composites. The research has matched physical experiments with Finite Element (FE) modelling. Four types of glass-fibre reinforced epoxy matrix composite structural elements were designed and manufactured to assess this application of DIC. The first two types of structural elements were flat coupons containing fully embedded delaminations, artificially introduced using two different methods. It was found that by placing these specimens in three-point bending, near surface delaminations, one ply below the surface being monitored, would cause a plateau in the surface strains. This plateau in strains was used to measure the embedded defect sizes. The size of the delamination was consistently overestimated from the interpretation of the strain fields. This was improved with the assistance of FE modelling to identify the relationship between the feature and the delamination. Pulse thermography was found to be a better technique for measuring the size of these defects. The third type of specimen was a flat coupon containing a milled-slot, which was fatigued to grow a delamination at the foot of the milled slot, and the delamination measured visually. For this specimen, the DIC results showed good correlation with the visually determined delamination lengths with an empirical fit applied to the strain results. Both lock-in thermography and pulse thermography were used to measure the delamination size of the same specimens and showed reasonable correlation with the visually determined delamination lengths. Finally, tubular specimens containing embedded PTFE delamination-defects were fatigued at different ratios of tension and torsion. DIC of the specimens loaded at the fatigue load ratio at which the delaminations were grown could not be used to quantify the size of the delaminations. The work has shown that DIC can be used to monitor delaminations in some structural elements, however the type of loading needs to be considered to ensure sufficient influence on the surface strains to enable strain features that can be used to measure the size of delamination

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
NameEmailORCID
Ajmal, Osman Z.
Date : 28 September 2018
Funders : EPSRC, NPL
DOI : 10.15126/thesis.00849052
Contributors :
ContributionNameEmailORCID
http://www.loc.gov/loc.terms/relators/THSCrocombe, Andrew D.A.Crocombe@surrey.ac.uk
http://www.loc.gov/loc.terms/relators/THSOgin, Stephen L.S.Ogin@surrey.ac.uk
http://www.loc.gov/loc.terms/relators/THSJesson, David A.D.Jesson@surrey.ac.uk
http://www.loc.gov/loc.terms/relators/THSGower, Michael R. L.michael.gower@npl.co.uk
Depositing User : Osman Ajmal
Date Deposited : 11 Oct 2018 08:04
Last Modified : 09 Nov 2018 16:39
URI: http://epubs.surrey.ac.uk/id/eprint/849052

Actions (login required)

View Item View Item

Downloads

Downloads per month over past year


Information about this web site

© The University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
+44 (0)1483 300800