Tension–tension fatigue behavior of carbon nanotube wires

The tension–tension fatigue behavior of three types of as-received carbon nanotube (CNT) wires, comprising of 30-, 60-, and 100-yarn, was investigated. Fatigue tests were conducted at 35%, 50%, 60%, 75% and 80% of their ultimate tensile strengths which provided the fatigue life data (S–N curves). Their electrical conductivities were measured as a function of the number of cycles. Fatigue strength of the CNT wires at a given number of cycles decreased with an increase in the number of yarns. Their electrical conductivity increased with increase of applied fatigue load and number of fatigue cycles. Damage and failure mechanisms involved relative sliding of yarns in CNT wires leading to the formation of kink bands, followed by plastic deformation and then breakage of yarns. Microtomography density measurements provided the evidence that the increase in conductivity was due to the reduction of micro/nano voids between and inside the yarns, which decreased with increasing fatigue load and number of fatigue cycles.