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 fiber-direction 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.