A multiple field image analysis procedure for characterisation of fibre alignment in composites

A novel method is presented for the characterization of fibre misalignment in composite specimens. The method is based on analysis of low magnification images in which the local fibre direction can be inferred from the orientation of elongated features in the image. Specimen preparation procedures and the image analysis algorithm employed are presented and their usage is illustrated by application to two types of carbon fibre composite, one of which showed a high degree of alignment while the other exhibited noticeable fibre waviness. Factors affecting the choice of certain image analysis parameters are briefly explored. Comparisons are presented with results obtained using conventional sectioning, followed by measurement of the aspect ratios exhibited by individual fibres. It is shown that the proposed method is robust, sensitive and experimentally convenient. It is particularly well suited to the characterization of specimens exhibiting significant variations in fibre alignment direction over large distances, i.e. pronounced fibre waviness, and the potential utility of such measurements for the prediction of compressive strength is highlighted.