Investigation of the deformation behavior and mechanical characteristics of polycrystalline chromium-nickel alloys using molecular dynamics.

In this study, the mechanical properties and plastic deformation responses of nanocrystalline Cr-Ni alloy were investigated via tensile tests by molecular dynamics (MD) simulation. The effect of various compositions, various grain sizes (GSs) from 4.7 to 11.0 nm, and various temperatures from 300 to 1500 K is analyzed. The results indicate that the yield strength of the polycrystalline Cr-Ni alloy decreases as decreasing GS, which shows the inverse Hall-Petch relation in the metal softening as reducing GS.  Young's modulus (E) increases in the order of the increasing GSs and single crystalline. E rises as raising the percent of Ni from 5 to 15% and then decreases as increasing %Ni to 20%. Besides, E is the linear decrease function with increasing temperature. The maximum stress decreases as increasing temperature and increasing %Ni from 5 to 15%. But that decreases as increasing %Ni from 15 to 20%. The maximum stress value of single crystalline is smaller than that of polycrystalline. The high shear strain zones depend on the GS and alloy composition. The shear strain zones focus on the grain boundary at a low temperature and disperse over the entire specimen when the specimen works at a high temperature. The reason is that the grain boundary helps release stresses to prolong the plastic deformation period to prevent rapid specimen destruction.

Anisotropic crack propagation and self-healing mechanism of freestanding black phosphorus nanosheets.

In this study, an indentation simulation is employed to study the anisotropic crack propagation and re-forming mechanism of freestanding black phosphorus (FBP) nanosheets by molecular dynamics simulation. The results indicate that the size of the FBP nanosheet decides the crack direction as well as the von Mises stress concentration. It is found that crack directions are not influenced by temperature. With increasing specimen size, the crack propagation rate is nearly the same as at the first stage of crack formation, while in the later stage, cracking develops very quickly in larger specimens. Especially, small FBP nanosheets almost re-form in a short time at ambient temperature. However, after being destroyed, the larger specimen has no possibility of recovery. Besides, when increasing the number of layers of FBP, the energy stored by the top layer and the system undergoing deformation increases. In addition, the specimen with two fixed edges is less stable, leading to increased stress and decreased Young's modulus compared with the specimen with four fixed edges.