Hybrid carbon nanotube - carbon fiber composites for high damping

Carbon nanotubes (CNTs) are known to increase damping in continuous fiber reinforced polymer composites without a loss of stiffness, which is important for designing materials for vibration- and weight-sensitive aircraft structures. The purpose of the current investigation is to explore new types of hybrid CNT - carbon/epoxy composites tailored for high damping and stiffness. Initially, different CNT surfactant treatments, orientations, and concentrations were evaluated. Based on this comparison, the material system with the best performance was identified and the dynamic behavior of this system was further investigated using a [0/±45]_s laminate subjected to different cyclic strain excursions and different temperatures. It is shown that a 10% volumetric concentration of highly aligned CNT yarns treated with a non-ionic surfactant, located at the interlayers and oriented along the loading direction, provides superior damping and stiffness characteristics. Damping increased monotonically with increasing cyclic strain amplitude, but was nearly insensitive to the mean strain. For a tensile strain amplitude of ~3000 με, the loss factor, loss modulus, and storage modulus of a hybrid [0/±45]_s laminate increased by 454%, 529%, and 14%, respectively, due to the addition of CNT yarns. Sensitivity of the dynamic properties to elevated temperatures was slightly increased in the hybrid laminate due to the surfactant, although the room temperature tensile strength was nearly unchanged in comparison to the baseline laminate.