Strain controlled fatigue response of large-scale perfect and defect nickel nanowires: A molecular dynamics study

Abstract

In this study, the response of the nickel nanowire (NW) subjected to constant strain amplitudes in the range of 0.02–0.12 during cyclic deformation is investigated. The studies are carried out using molecular dynamics (MD) simulations on perfect and defect nickel NW containing ∼ 925,965 atoms. Embedded atom method (EAM) potential is used to model the interactions between nickel atoms. Initially, tensile test is conducted to determine the yield stress and yield strain of the NW at strain rate of 109 s−1 and temperature of 300 K. The yield stress is observed to be 14 GPa and the corresponding strain is 0.17. The cyclic deformation tests are carried out at a temperature of 300 K. During the cyclic deformation at strain amplitudes of 0.02 and 0.04 the plastic deformation features such as slip lines or slip bands do not appear on the surface of the NW's even after 1000 cycles of straining. These features surface when the strain amplitudes are above 0.04 and their density increase with the strain amplitude and cycles. The NWs exhibit asymmetric stress-strain (compression-tension) hysteresis loops at all the strain amplitudes and up to 1000 cycles. The compressive stress is observed to be higher than the tensile stress for all the cycles. The defect nickel NWs have also exhibited similar behavior as that observed in perfect NWs. Further, it is observed that the width of the loops increases with an increase in the strain amplitude and also with the number of cycles due to softening. The NWs did not fracture even after cyclic deformation for 1000 cycles which could be due to the lower strain amplitudes employed in the present study. Cylindrical shape NWs of different sizes are also investigated by subjecting to similar cyclic deformation conditions as above and are found to show similar behavior.