Cyclic deformation of ultra-fine and nanocrystalline metals through nanoindentation: similarities with crack propagation

Cyclic nanoindentation loading is a localized fatigue test providing very useful informations on dynamic damage phenomena of nanostructured materials. The main goal of the present paper is to examine ultra-fine and nanocrystalline metals fatigue through cyclic nanoindentation experiments. In the present study berkovitch indentations were performed in order to evaluate monotonic indentation stress–strain curves and cyclic indentation stress–number of cycles diagrams. Multi-step indentation allows for a rapid evaluation of variation of mechanical properties with increasing depth and in combination with single-step indentation response, is indicative of deformation induced structural changes in the material. In addition, it is put in evidence the depth propagation behavior under cyclic loading simulating a fatigue crack propagation. Such technique is very attractive for the evaluation of fracture toughness.