Characterisation of random carbon fibre composites from a directed fibre preforming process: Analysis of microstructural parameters

This paper seeks to quantify the influence of microstructural parameters on the mechanical and physical properties of carbon fibre laminates produced by automated directed fibre preforming. The main objective was to establish whether a correlation exists between local areal density variation and mechanical performance. The parameters studied were fibre length, tow filament count and laminate thickness. A statistical process simulation was developed to predict preform density variation and the results were compared with experimental tensile properties.In general, consistent preforms with low areal density variations exhibit higher mechanical properties. There was a notable reduction in areal density variation and consequently an increase in tensile properties with shorter fibres (75–25 mm) and thicker laminates (1.5–4 mm for a constant volume fraction). The effect of filament count was less clear. Simulations indicated that filament count was the most significant parameter in terms of areal density variation; with low filament counts improving density variation by up to 50% (6 K compared with 24 K). However, no variation in tensile properties was observed because of a secondary filamentisation effect caused by the fibre surface treatment.