Augmenting mode-II fracture toughness of carbon fiber/epoxy composites through carbon nanotube grafting

Systematic experimental investigation is carried out to characterize the effect of carbon nanotubes (CNTs) grafting on the average mechanical properties and mode-II fracture toughness of carbon fiber reinforced plastics (CFRPs). Two growth strategies are used in a chemical vapor deposition (CVD) reactor to ensure uniform coverage of both sides of fiber fabric with CNTs. Improvement in interlaminar shear strength of CFRP due to incorporation of CNTs is found to be sensitive to the uniformity of grafted CNTs on the fabric surface. It is shown that the use of optimum CNT grafting strategy on the fiber surfaces leads to a significant improvement in flexural properties and mode-II fracture toughness of conventional CFRPs. However, the use of CNT grafted laminas in the composite laminate does not alter the response of CFRP under the uniaxial tensile loading. Scanning electron microscopy (SEM) analysis of failed composite coupons after mode-II testing reveals that different failure mechanisms operate in composite laminate fabricated with or without the use of CNT grafted laminas.