Abstract: An experiment method is developed to investigate the low-cycle fatigue fracture behavior of nano-material interface. Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM) are used in the experiments. With FIB, a nano-cantilever specimen consisting of a copper (Cu) layer of 200-nm-thick and a silicon nitride (SiN) layer of 1000-nm-thick on a silicon (Si) substrate is fabricated from a macroscale multi-layered material (Si/Cu/SiN). Using a minute loading apparatus, the cyclic loading experiment is conducted in TEM, and the low-cycle fatigue fracture of Cu/Si interface in different specimens is in situ observed. The fatigue strength of Cu/Si interface is around GPa level owing to the high yield stress of the Cu nano-film and the deformation constraint associated with the neighboring hard materials. The S-N curve shows clear dependence of fatigue life on the applied stress in the high stress range and the existence of a fatigue threshold at low stress range. Moreover, the high ratio of fatigue limit to the fracture stress in a monotonic loading suggests the brittle behavior of the interface in nanoscale materials.

Key words: engineering mechanics, fatigue, interface, delamination damage, nanoscale, in situ experiment