Stochastic Characterisation of the In-Plane Tow Centroid in Textile Composites to Quantify the Multi-scale Variation in Geometry

Abstract

Optical imaging is performed to quantify the long-range behaviour of the in-plane tow centroid of a 2/2 twill woven textile composite produced by resin transfer moulding. The position of the carbon fibre tow paths is inspected over a square region of ten unit cells and characterised by decomposing the centroid data into a non-periodic non-stochastic handling effect and non-periodic stochastic fluctuations. A significantly different stochastic behaviour is observed for warp and weft direction. Variability of the in-plane coordinate, identified by the standard deviation, is found to be six times higher in weft direction. The spatial dependency of deviations along the tow demonstrates a correlation length of ten unit cells for warp tows, which is twice the length computed for weft tows. The observed bundling behaviour of neighbouring tows of the same type is quantified by a cross-correlation length. Warp tow deviations affect neighbouring centroid values within the unit cell dimension, while this effect exceeds the unit cell size for weft tows. The stochastic information reflects the difference in tow tensions during the weaving of the fabric.