Interlaminar shear strength of carbon/epoxy composite with aligned carbon nanotube yarn interlayers

Carbon nanotubes can provide significant vibration damping to carbon/epoxy composites, which is a benefit for high vibration applications such as rotorcraft. One means of maximizing the volumetric concentration of CNTs, and thus damping, in composite laminates is to concentrate the CNTs in the interlayer regions rather than disperse them throughout the matrix. Also, aligning the CNTs along the principal strain direction maximizes damping. However, there is concern that the weak CNT/epoxy bond will compromise the interlaminar shear strength (ILSS) of the laminate. The current investigation aims to evaluate the ILSS of unidirectional carbon/epoxy with an interlayer consisting of CNT yarns. The ASTM D2344 short beam strength (SBS) test is used to evaluate the ILSS of 0-deg. unidirectional carbon/epoxy with a single layer of aligned CNTs at the midplane, where failure occurs predominantly due to the applied shear stress. The main variables in the tests are the non-ionic surfactant and the orientation of the CNTs (parallel or perpendicular to the shear direction). The SBS results indicate negligible reduction in ILSS due to the addition of just surfactant to the composite, although the glass transition temperature of the composite is reduced by 10°C. Upon the addition of surfactant-treated CNTs parallel to the shear direction, the ILSS reduction relative to the baseline material is small (4%). When the surfactant-treated CNTs are oriented perpendicular to the shear direction, the reduction in ILSS relative to the baseline is also small (8%). It is concluded that adding concentrated surfactant-treated CNT interlayers to carbon/epoxy laminates has a small adverse effect on ILSS and glass transition temperature.