Synergetic effects on the mechanical and fracture properties of epoxy composites with multiscale reinforcements: Carbon nanotubes and short carbon fibers

The ball-milling/liquid-phase oxidation (BMLPO) method was used to fabricate surface-modified short carbon fibers (SCFs). Multiscale epoxy composites reinforced with a combination of SCFs and multiwalled carbon nanotubes (MWNTs) were prepared. Atomic force microscopy observations and contact angle measurement were used to investigate the modification effect of the BMLPO method. Mechanical tests and scanning electron microscopy observations were used to study the effects of the SCFs, MWNTs, and their combination on tensile properties, impact strength, and fracture toughness of the epoxy composites. The results show that the surface roughness of the SCFs after BMLPO treatment increased, and the wettability of the SCFs was improved as well. The combined use of the SCFs and MWNTs had a synergetic effect on the tensile strength, fracture toughness, and impact strength of the epoxy composites. The addition of MWNTs promoted the plastic deformation of the epoxy matrix and decreased the stress-concentration level near the SCF/matrix interface; these were considered the main causes of the synergetic effect. (C) 2016 Wiley Periodicals, Inc.