Characterisation and modelling of the shear-tension coupling and variability of woven engineering fabrics

Abdiwi, Farag Abdussalm Ali (2013) Characterisation and modelling of the shear-tension coupling and variability of woven engineering fabrics. PhD thesis, University of Glasgow.

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Woven engineering fabrics generally serve as advanced composite preforms and are an important class of engineering material. This thesis focuses on improving the accuracy of Computer Aided Engineering (CAE) tools for simulating the deformation of such materials during the press-forming manufacture process. Specifically, this has involved better understanding: (i) the material behaviour during deformation and (ii) the extent and influence of material variability on forming behaviour. To this end, the use of a novel fabric shear test, the BBE test, capable of characterising the shear-tension coupling of engineering fabrics has been used for the first time in an extensive characterisation program, involving three different woven engineering fabrics. Results show a strong dependence of shear compliance on in-plane tension. Wrinkling behaviour during shear has also been characterised using two new analysis methods, a transmitted backlighting technique and a tracer line analysis technique. The onset of wrinkling is clearly shown to be an increasing function of the in-plane tension applied to the deforming fabric. Variability of fibre orientation, otherwise known as ‘tow meander’ can degrade the final mechanical properties of a textile composite part and can also influence measurements of the fabric’s shear compliance. Accordingly, variability of tow orientation in a pre-consolidated textile composite and three engineering fabrics has been characterised using two different image processing methods: a simple manual method and a semi-automated method. The latter has been found to be a promising tool in terms of increasing accuracy and in reducing manual effort during the characterisation process. Modelling tow meander has also been conducted using a numerical code, VarifabGA, that has been developed during the course of this work. The code has allowed the effects of tow meander on shear compliance to be investigated in numerical simulations using a technique of assigning an initial fibre orientation to each element in a Finite Element (FE) mesh before conducting shear test simulations. The experimentally measured shear-tension coupling has also been modelled by enhancing a pre-existing Non-Orthogonal Constitutive Model (NOCM). A comparison between model predictions and experimental results of the sensitivity of this shear-tension coupling has shown that the model provides good results. Finally, a novel geometrically complex 3D forming tool of a kart wheel has been designed and manufactured for use in experimental and numerical forming studies. The part provides a challenging modelling problem with which to demonstrate the use of the new computational tools developed during the course of this work.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Coupling, engineering fabrics, biaxial bias extension test, wrinkling, Varifab, VarifabGA.
Subjects: T Technology > TJ Mechanical engineering and machinery
T Technology > TS Manufactures
Colleges/Schools: College of Science and Engineering > School of Engineering > Systems Power and Energy
Supervisor's Name: Harrison, Dr. Philip
Date of Award: 2013
Unique ID: glathesis:2013-4246
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 09 May 2013 14:37
Last Modified: 23 May 2016 13:55

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