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Prepreg forming numerical analysis and experimental characterisation for a novel high-volume forming process
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Pasco, Corentin (2018) Prepreg forming numerical analysis and experimental characterisation for a novel high-volume forming process. EngD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3494483~S15
Abstract
With stringent emission standards being introduced, the demand for lightweight materials in the automotive industry has significantly increased. The use of carbon fibre reinforced plastics (CFRP) in automotive structures could deliver significant weight saving over more traditional materials, without having to compromise on other mechanical properties. However, high costs and long production time have precluded their use for volume application. Aston Martin have identified a novel manufacturing process which could produce CFRP parts economically by utilising rapid-cure prepregs. The integrated process consists in the combined application of double diaphragm forming with compression moulding techniques to produce a single-step manufacturing process.
A challenging step identified in the manufacture of CFRP components is the forming of initially flat laminate into a three-dimensional shape. Due to the flexible and inhomogeneous nature of the reinforcement, the composite blank can undergo severe deformation such as wrinkling which compromises the mechanical performances of the final component. To predict these defects, forming simulation tools can be used in the product design phases. Within this project, a commercial forming simulation software is used to support the development of this novel manufacturing process.
During forming, the fibrous reinforcement is subjected to several deformation modes, including intraply shear, interply shear and out-of-plane deformation. Within the software, these mechanisms are represented using material models, which are defined by input data. These are obtained through extensive characterisation of the uncured materials. In this work, the mechanical properties of a 2x2 twill woven and a unidirectional (UD) epoxy prepregs are investigated, under conditions representative to those expected during the manufacturing process, including, high deformation rate, elevated temperature and high normal pressures. To that aim, novel characterisation test methods were developed to evaluate the material behaviour under these specific conditions.
Experimental forming experiments were carried out for each material, with three different lay-ups using a double-dome benchmark tool and a representative numerical model was setup. Comparisons between experimental and numerical results (in terms of material draw-in, defects position, shear angle and relative ply slippage) demonstrate the ability of the software to predict the deformation of the woven prepreg. For the UD prepreg, two modelling approaches are used: (1) a single ply approach where each ply is modelled using a UD material model, and (2) a cross-ply approach which relies on a woven fabric material model. Simulation results demonstrate that for the prediction of defects, the single ply approach provides better results. In addition, unlike the cross-ply approach, the model is able to identify areas of high stress perpendicular to the UD fibres, which may indicate ply splitting. For both approaches, the prediction of material draw-in is however challenging since it is influenced by fibre splitting, which cannot be modelled in the simulation.
Item Type: | Thesis (EngD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TP Chemical technology T Technology > TS Manufactures |
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Library of Congress Subject Headings (LCSH): | Carbon fiber-reinforced plastics, Thermosetting composites, Epoxy resins, Manufacturing processes | ||||
Official Date: | 30 September 2018 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | EngD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Kendall, Kenneth N. ; Maggs, Steven J. ; Khan, Muhammad Aurangzeb | ||||
Sponsors: | Engineering and Physical Sciences Research Council ; Aston Martin Lagonda Ltd. | ||||
Format of File: | |||||
Extent: | xix, 195 leaves : illustrations, charts | ||||
Language: | eng |
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