An investigation into the influence of fabric weaves on the consolidation of commingled thermoplastic composites was undertaken. The study was carried out to investigate the influence of fabric weaves on the fibre volume fraction of composites and the resultant effect on the mechanical properties of the composites. Furthermore the correlation between changes in composite void content with changes in the consolidation parameters and the changes in composite thicknesses was also investigated. Four samples representing some of the common preform weave styles used in the production of thermoplastic composites were selected for experimental and theoretical investigations. The sample weaves were, Plain, 2x2 twill, 4x4 twill and unidirectional plain weave. In order to study the influence of preform weaves on the melt impregnation of commingled fabrics, dry preform modelling was carried out to develop a method for predicting nesting in multilayer stacking of plain and nonplain woven preforms. This allows for the prediction of the fibre volume fraction of the dry preform before the onset of melt impregnation. Experimental measurements using the samples show a good correlation between the models and experimental data. Void fraction measurements were carried out using optical microscopic methods. The consolidated samples were subjected to tensile, shear and flexural tests to assess their mechanical properties. Results indicated that preform weaves strongly influenced the consolidation quality measured as a function of the void content and the mechanical properties of the composites. Fabrics with fewer interlacements generally consolidated into composites with void contents lower than fabrics with higher number of interlacements at lower consolidation temperature and pressure. This is due to lower fibre volume fraction and larger inter-tow pore spaces, which is due to very low inter-layer nesting. However, at higher temperatures, void contents of composites consolidated from fabrics with higher interlacements were lower than those consolidated from fabrics with fewer interlacements. This is attributed to nesting within the preform leading to reduction in the pore size of the inter-tow spaces coupled with the reduction in matrix viscosity. The changes in composite thickness as the processing parameters were varied were found to correlate closely with changes in the void content of the corresponding composite. This led to the conclusion that changes in composite thickness can be used as a measure of consolidation quality. This is important as it allows for quick measurements to be taken without the need for tedious void content measurements. Mechanical properties of the composites indicate that preforms with longer float length had better tensile, interlaminar shear and flexural properties. However, unidirectional preforms with little or no transverse bridging fibres tend to be pushed apart during matrix impregnation resulting in resin rich areas. This ultimately results in poorer interlaminar bond strength.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:515219 |
| Date | January 2010 |
| Creators | Ogunribido, Abiodun Oludare |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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