Improving compressive strength of high modulus carbon-fiber reinforced polymeric composites through fiber hybridization

There has been a strong demand in using high-modulus (HM) carbon-fiber composites potentially enabling lightweight aircraft structures with significant weight savings. However, extremely low fiber-direction compressive strength has been a well-recognized weakness of the HM composites, prohibiting their implementation in aircraft platforms. Hybridizing fibers with varying moduli provides an innovative means for improving the fiber direction compressive strength of composites. This has been implemented by comingling intermediate-modulus (IM) and high-modulus (HM) carbon fibers in HM carbon fiber reinforced polymer (CFRP) toughened with nano-silica. Comingling IM and HM fibers at the filament level in addition to the matrix nano-sized structural reinforcement throughout the composite, increases shear modulus to axial modulus ratio of the composite material, thus improving microstructural stability likely governing the fiber-direction compressive strength behavior. The basis for this new material design stems from the fact that fiberdirection compressive strength increases with the shear modulus to axial modulus ratio of composites across different fiber and resin combinations. The results demonstrate that the new hybrid HM composite fiber-direction compressive strength achieves that of IM legacy composites but with more than 30% higher axial modulus. (C) 2019 Published by Elsevier Ltd.