Molecular dynamics study of fatigue behavior of nickel single-crystal under cyclic shear deformation and hyper-gravity condition

Abstract

Dynamic mechanical properties play an essential role in governing the intrinsic fatigue behavior of superalloys. In this work, [001](010), [110](-110), and [101](010) pre-existing center cracks model of nickel single crystals under increasing cyclic shear deformations were studied by molecular dynamics simulations. More importantly, we introduced three hyper-gravity forces, i.e., 3⨯1012 g, 4⨯1012 g, and 5⨯1012 g, during the fatigue deformation to simulate the high-speed rotation of the blade. The stress intensity factor for the first dislocation nucleation indicates that the critical stress is strongly dependent on the hyper-gravity intensities and temperatures. The fatigue life decreased rapidly with the elevated hyper-gravity strength. Moreover, the [001](010) crack propagation shows a brittle-to-ductile transition at temperatures below 300 K and is suppressed at high temperatures. The crack length in the relation to hyper-gravity intensities is discussed and shows anisotropy along the direction of hyper-gravity. No crack propagation is observed in [110](-110) and [101](010) central crack models.

The Microstructural Evolution of Nickel Single Crystal under Cyclic Deformation and Hyper-Gravity Conditions: A Molecular Dynamics Study

“…To generate the hyper-gravity environment at the atomic scale, we introduced a constant force that pointed along the hyper-gravity direction to each atom. Recently, such a hyper-gravity loading scheme has been reported by molecular dynamics and phase-field simulations [21,28]. In addition, the effect of rotation that introduces too many variables and makes the analysis difficult is ignored.…”

“…Zhou et al [20] extracted the da/dN metrics from the fatigue crack growth in polycrystal coherent twins. Recently, we applied hyper-gravity loading to study the fatigue behavior of nickel under cyclic shear deformation [21]. The critical stress is strongly dependent on the hyper-gravity intensities and temperatures.…”

Molecular dynamics simulation of effects of loading parameters on fatigue crack growth behavior in titanium single crystal

“…This phenomenon was attributed to the fact that higher temperatures make it easier to break atomic bonds, leading to lower resistance to crack propagation 17 . Xiao et al 18 revealed that the stress intensity factor K showed a strong temperature dependence during crack propagation. In addition, Tang et al 19 observed that the FCGR of magnesium decreased with increasing temperature and strain rate along a specific orientation.…”