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

A novel method is presented for the characterisation of fibre misalignment in composite specimens. The method is based on analysis of low magnificatio n images in which the local fibre direction can be inferred from the orient ation of elongated features in the image. Specimen preparation procedures a nd the image analysis algorithm employed are presented and their usage is i llustrated by application to two types of carbon fibre composite, one of wh ich showed a high degree of alignment while the other exhibited noticeable fibre waviness. Factors affecting the choice of certain image analysis para meters are briefly explored. Comparisons are presented with results obtaine d using conventional sectioning, followed by measurement of the aspect rati os exhibited by individual fibres. It is shown that the proposed method is robust, sensitive and experimentally convenient. It is particularly well su ited to the characterisation of specimens exhibiting significant variations in fibre alignment direction over large distances, i.e. pronounced fibre w aviness, and the potential utility of such measurements for the prediction of compressive strength is highlighted. (C) 2001 Elsevier Science Ltd. All rights reserved.