Experimental and Microscopic Investigation on Mechanical Performance of Textile Spread-tow Thin Ply Composites

Textile non-crimp carbon fabrics (NCCFs) are made of several dry uni-directional (UD) tows which are aligned straight and stitched together. The use of these reduces resin rich areas and stress concentrations that are likely found in woven fabrics composites during manufacturing. The use of spread tows to manufacture the thin plies leads to the fibre areal weight (FAW) of lower than 150 g/m2. This current research aims at investigating the tensile, flexure and interlaminar shear response of thin ply carbon composites with a view to deduce the failure mechanisms. The baseline comparison is carried out with conventional thick ply composites and differences in the failure mechanisms are studied. For tensile tests, reduced number of acoustic emission counts in the case of thin ply composites indicated that the stresses were unaffected until the laminate ultimate strength. In flexural tests, it was noticed that the resin rich sites near the stitches first initiated compression failure followed by translaminar cracking or longitudinal fibre fracture. This is due to the strong fibre-matrix adhesion in the case of thin ply composites. No interlaminar shear fracture was seen to occur throughout the laminate thickness and across the width, leading to a significant improvement in the flexural properties of the thin ply composites. These thin laminates have better interlaminar shear properties. It was observed through microscopy that thin ply laminates first undergo interlaminar shear followed by inelastic deformation at the ultimate strength of the material.