Little is known about the fatigue properties of nanocrystalline materials or the effect of prolonged cycling on their internal structure. For example, it could be speculated that continuous deformation would lead to extensive grain growth. An initial set of fatigue experiments have been carried out on nanocrystalline Cu, with

the primary goal of examinin g the stability of the internal structure under cycling. In addition, external surfaces were examined for possible clues to deformation mechanisms.