Estimation of three-dimensional fibre-orientation distribution in short-fibre composites by a two-section method

The overall fibre orientation in a composite can be statistically characterized by a fibre-orientation distribution. Fibre-orientation studies have concentrated on two major areas: those dealing with continuous fibres and those dealing with short fibres. This paper presents a novel two-section based method for statistical characterization of the fibre-orientation distribution within short-fibre composites. This method produces unbiased distribution data for the near-zero misalignment angles and simultaneously resolves the orientation-duality problem. The method's novelty lies in its ability to determine accurately (within 1 mum) the relative positions of two sections. While taking advantage of the extra information provided by the two sections, the proposed method also makes use of the single-section method's main principles, namely: (1) intersection of a plane and a cylindrical fibre is an ellipse and (2) the ellipse's shape is a function of fibre's orientation relative to the intersecting plane. Therefore, by sectioning a specimen, acquiring images of the cross-sectional surfaces, and collecting the fibre-ellipse data from these images, the orientation of every fibre intersecting the sectioning plane can be determined. The probability distribution for fibre orientations within the sectioning plane is then related to that within the specimen volume.