Fatigue behaviors of diamond-like carbon films

& nbsp;This work investigates the fatigue behaviors of diamond-like carbon (DLC) films by conducting cyclic tensile tests and interfacial fatigue tests via molecular dynamics. It is found that the strength of DLC films is reduced with the increasing cycle number due to the irreversible sp(3)-sp(2) transition of carbon atoms induced by tensile deformation. Regions with high sp(2)C fraction are easy to deform owing to their weak strength, thus the atomic strains are almost localized in such regions. The weakest region is regarded as the defect of the films and suffers from the most severe strain localization. As a result, many sp(3)C atoms are transformed into sp(2) hybridization in the defect, destroying the integrity of sp(3)C network. Hence, the film failure occurs in the defect because of its badly degraded strength. Furthermore, interfacial fatigue of DLC films is induced by the sp(3)-sp(2) transition during the cyclic tensile tests.