Improved interlaminar fracture toughness of carbon fiber/epoxy composites by a combination of extrinsic and intrinsic multiscale toughening mechanisms

Carbon fiber reinforced polymer (CFRP) composites with hierarchical structure interleave composed of nanoscale core-shell rubber (CSR) and microscale short carbon fiber (SCF) were fabricated. The hierarchical structure interleave exhibits superior interlaminar toughening efficiency than either CSR or SCF alone. Triggering intrinsic and extrinsic toughening mechanisms at different scales by CSR and SCF, respectively, the mode-I critical energy release rate (GIC) and mode-II critical energy release rate (GIIC) of multi-phase interleaved CFRP composite are 127% and 154% higher than those of unmodified sample. While the tensile properties and glass transition temperature (Tg) are not compromised. The fracture toughness of epoxy/CSR system was also investigated to better understand the effect of matrix toughness on interlayer toughness of CFRP. Numerical analysis and fracture surface observations revealed the synergistic toughening mechanisms in SCF/CSR interleaved CFRP composites. The synergy between nanoscale intrinsic toughening mechanism and microscale extrinsic toughening mechanism, evolving with crack propagation, contributes to a greater energy absorption. The usefulness of the present study for preparation of high-performance CFRP is discussed.