T700 or T300 with Nano-/Micro- Aramid fiber mechanical cross-linking: Flexural properties of carbon fiber composites before and after impact

• T300 toughened by nano-/micro-Aramid pulp outperform T700 under bending before and after impact. • Mechanical cross-linking between plies is created in ultra-thin interlays < 20 μ m. • Flexural strength of T300 with 6 g/m 2 AP increased by 49 % before impact and by 68 % after impact. • Both interlayer thickness and interlayer fiber volume density are crucial for Z-directional cross-linking. • Short-beam-shear strength of T300 with AP cross-linking is 40% higher than T700. Flexural and compressive failures of carbon fiber composites, more critical than direct tensile failure, imply T700 with higher tensile strength (about 40 % higher than T300) can still be outperformed by T300 in flexure and compression through careful composite microstructure designs. We show mechanical cross-linking from nano-/micro- Aramid Pulp (AP) fibers of a few hundred microns in length can be generated if the interleaving thickness is reduced to around or below 20 μm. Flexural properties of T300 with mechanical cross-linking from AP (4–6 g/m 2 ) are more superior than those of T700, both before and after low energy impacts. Up to 40 % and up to 50 % increase in shear and flexural strengths were observed. This work compared flexural properties and impact resistance of T700 and AP toughened T300 composites, showing the importance of structural design (e.g. using thin layer interlayer AP cross-linking) for higher strength and toughness simultaneously.