The susceptibility to delamination is one of the main concerns in fiber
reinforced polymer composites (FRPs), while carbon nanotubes (CNT) carry
the promise of enhancing this poor out-of-plane mechanical performance.
This work reviews the progress to date towards methods of integrating
CNTs into FRPs, along with a summary of the measured improvements in the
mechanical properties (especially in fracture toughness) of the
resultant hierarchical composites. The CNTs loading, type and
orientation effects on fracture toughness of resultant laminates are
discussed in detail in order to enable us to wisely select the best
combination and thus maximize the reinforcing potential of CNTs.
Toughening mechanisms of CNT-toughened laminate at different length
scales are systematically reviewed as well. In experimental part, a
facile and scalable approach are presented, by which CNT fibers with an
unusual yarn-like structure can be perfectly integrated into structural
laminate composites. Interlaminar fracture toughness (IFT) of resultant
products was determined in Mode I (opening mode) test and crack
propagation mechanisms are analyzed by means of optical microscope, SEM,
and Raman analysis. Finally, brief conclusions are summarized together
with a detailed discussion on the future work.