Characterising microstructural organisation in unidirectional composites

Understanding the three-dimensional variability of unidirectional composites is relevant to the material performance and the development of advanced material modelling strategies. This work proposes a new methodology for the characterization of unidirectional composites, showcased on carbon fibre/poly(ether-ether-ketone) tapes. Three microstructural descriptors were here introduced, each representing an increasing level of complexity in the fibre architecture: from a tortuosity-based single fibre trajectory analysis to fibre groups’ behaviour, to fibre network interconnectivity. The methodology was developed and validated on real material datasets acquired via X-ray computed tomography. A facile method for image analysis was used to reconstruct the three-dimensional fibrous architecture at a single fibre path resolution. The approach bridges a gap in the traditional approach and nomenclature typical of the composite field to describe and quantify complex fibre organization in unidirectional composites, highlighting micro- and mesoscopic features, such as edge-core effects in the fibre arrangement, possibly occurring in tow spreading. The study of the parameter interdependence showed relationships, which will provide further insight for future research in the study of microstructure formation of unidirectional composites, its evolution during processing or loading, and input for advanced modelling techniques based on Representative Volume Elements.