Characterization of the fatigue properties of a hybrid composite utilized in high voltage electric transmission

The fatigue properties of a unidirectional carbon/glass/epoxy hybrid composite used as the load bearing member of the next generation high voltage transmission lines were evaluated. It was found that the composite showed a strong sensitivity to the amount of transverse loading when tested using the rotating beam method. These results indicate that the bearing stress at mechanical connections must be considered for effective fatigue life design. At the lowest stress amplitude evaluated in this research, the hybrid composite material exhibited run-out behavior. For the remaining stress amplitudes, the S-N behavior of the hybrid composite material was well described by a “Basquin type” power law relationship. It was also found that the composite exhibited a period of “wear-in” behavior in which the composites' axial modulus increased substantially. This increase was attributed to a change in the alignment of the reinforcing fibers under the influence of an applied load.