Morphological analysis of the fibres random distribution in unidirectional composite lamina by digital image processing

The prediction of the transversal strength of long fiber reinforced composite materials plays a significant role in designing components made with these materials. Since failure is mainly a local phenomenon, the random distribution of fibres and the local fiber packing density in the transverse section have to be taken into account, under the hypothesis they are the dominant parameter of the problem. This paper describes a methodology to analyze the stress of a transversally loaded long-fiber composite lamina. The fiber distribution has been obtained by an image processing of a lamina cross section by which a finite element evaluation of the stress and a final statistical analysis were performed. The effects of the local fiber density on the stress distribution and, consequently, on the predicted strength are presented, demonstrating the effect of fiber density on the probability of transversal failure. A linear correlation between local stress and packing density has been demonstrated thus suggesting the possibility to develop a predictive strength model based only on the average local packing density.