Formability of multi-matrix composites

• Main Author: Turk, Mark A
• Format: Dissertation
• Language: English
• Published: University of Bristol 2022
• Subjects: FEA; Formability; Infusion; Modelling; Multi matrix; Preform; RTM

Multifunctionality in composites is a developing area of research which shows much promise for the production of efficient and integrated structural designs. Incorporating further functionality criteria on top of the basic requirement for structural strength provides a range of possibilities for weight saving. Formability of functionalized preforms has not yet been fully explored and presents the main subject of this thesis. Most current development in multifunctional composites is focussed around functional materials. However, often functionalization, i.e. by incorporating micro/nano-additives, makes materials less compliant, handleable, or formable. An alternative approach explored in this thesis is to create multifunctional structures by separating the domains. The creation of multi-matrix structures, where two matrix materials occupy separate zones of a continuous fabric, is a relatively unexplored field with no established manufacturing process. The primary benefit is the ability to provide multifunctionality in carefully tailored regions, allowing the manufacturer to designate areas as either multifunctional or purely structural based on design requirements. This is especially relevant when the multifunctional component inhibits formability, requiring the addition of flexible 'hinges' between multifunctional regions. This thesis tackles many of the manufacturing hurdles and presents an effective technique for the creation of such structures. This work constitutes a part of the EPSRC Hub project on the manufacturing of multifunctional composites, where the contribution of this thesis focuses on the application of this technique towards enhancing the formability of structural supercapacitors This is developed in collaboration with Imperial College London, who have pioneered the development of structural supercapacitors. Multifunctional elements tend to inhibit formability, however their introduction can also be used to improve forming if applied wisely, the modification of textile properties in regions where a defect is likely to form can lead to formability enhancement. Forming of dry fibre textile pre-forms is a commonly used technique to achieve complex shapes for light weight composite structures. Most conventional engineering fabrics can only deform through shearing. Excessive shearing often results in the formation of detrimental features, such as wrinkles, folds and fabric distortions. Modification can be achieved by the integration of patches: additional materials, such as reactive thermally-conditioned resins, tufted or stitched yarns, thermoplastic films, locally activated binder, etc. This method is simple and effective for a certain class of forming problems. Once formed the primary structural resin is added and the patch material becomes a part of the finished component. The success of the forming operation depends on the balance of properties between dry and patched materials. This thesis shows the feasibility of improving formability by local modification of preforms and explores various numerical modelling tools for optimising this process. Modification is implemented by depositing localised resin patches onto textile preforms. The technique allows for continuity of fibres throughout the preform with the additional benefit that the deposited resin can be thermally staged to the desired level of cure to tune the viscosity of the region for forming and consolidation. The location and dimensions of patches are specified through numerical modelling to inform the subsequent manufacturing process. Manufacturing trials successfully demonstrate the possibility of defect mitigation using this technique.