Tensile failure strain and microstructure of unidirectional carbon fibre non-crimp fabric composites

UD non-crimp fabric (NCF) carbon/epoxy composites were tested in longitudinal tension to assess the influence of the stitching on the tensile failure strain of the carbon fibre layers. The composites made with the stitched layers had the same tensile failure strain as the reference non-stitched layer composite. A composite where the stitching yarns has been removed appears to have a lower failure strain though. Computed tomography images revealed that the regions adjacent to the stitch showed the highest fibre volume fraction. The stitched layers clearly showed a higher fibre misalignment than the non-stitched layers. The fibre misalignment was very low in the layers in which the stitches were removed. The observations suggest that the fibre distortions due to stitching do not reduce the failure strain; the distortions caused by removing the stitches are detrimental and reduce the failure strain.