Defect Development during the Preforming of Non-Crimp Fabrics

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The research questions that this PhD is trying to address are by what mechanisms do the defects such as wrinkles develop during the preforming of textile reinforcements and how can these defects be characterised and minimised. Textile reinforcements are a critical area of research within composite manufacturing as they provide a pathway towards more cost effective and faster production of composite components for the aerospace and automotive industries. However, currently the defects that develop during the preforming step of the manufacturing process pose a significant hurdle and thus this PhD attempts to address this issue. The textile reinforcements that are considered are non crimp fabrics (NCFs) which are novel multi-layered textiles that are stitched together instead of being woven. The approach for this PhD is to develop a novel experimental preforming rig that is able to track and measure the development of wrinkles and the associated fibre strains in the NCFs using 3D digital image correlation (DIC), under a variety of boundary conditions. This data will then be used to develop relationships between the strains and wrinkle amplitudes in order to attempt to develop a wrinkling forming limit diagram (WFLD) that is able to characterise the onset of wrinkling for a particular textile reinforcement in terms of the strains induced. The research will highlight a plausible standardised methodology for experimentally obtaining the wrinkling limits of a particular fabric from a series of simple tests, which can then be applied to a range of fabrics and significantly simplify the fabric selection process and their subsequent manufacture. Furthermore, the understanding of wrinkle development during forming obtained in these experiments will be used to inform the development of a micromechanical model finite element (FE) model of the forming of NCFs. This model will be able to predict the locations and amplitudes of wrinkles and the associated strains, and can be used directly to develop the WFLD for a particular fabric, without the need for any experimental tests. Ultimately, the PhD will attempt to conduct an optimisation study based on both experimental and simulation data that is able to optimise the preforming process with regards to minimising defects. This project fits within the EPRSC research area of 'Materials engineering - composites.'