Molecular dynamics simulations using embedded atom method inter-atomic potential were used to study crack propagation under cyclic loading in a Ni single crystal and a Ni-Al bi-metallic system. The crack in Ni-Al initiates and propagates from Ni towards the Ni-Al interface. The cyclic loading was applied in a strain controlled manner with constant amplitude of maximum strains (emax) applied to the two systems. The crack growth and propagation mechanism of a crack propagating in Ni were compared with the crack growth and propagation of a surface crack in Ni-Al at two different values of emax. Our results suggest that depending on the maximum value of the applied strain (emax), the crack propagates either by fatigue cleavage of the atomic bonds in the crack plane or by void nucleation in the regions near the crack tip. The creation of voids slows down crack growth in both the Ni and Ni-Al at higher value of emax. A comparison of crack growth under tensile and cyclic loading (emax, 0.046) suggest that plastic deformation around crack tip dominate crack propagation during tensile loading that result in slower crack growth (due to early nucleation of dislocations at the crack tip), when compared to crack growth under cyclic loading.

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