20 research outputs found
Investigation of point defect evolution and Voronoi cluster analysis for magnesium during nanoindentation
The present study investigates the effect of nanoindentation on single-crystal magnesium specimens using the embedded-atom method potential in molecular dynamics simulation. Analyses are done under dynamic loading where the load-bearing capacity and change in the structural configuration are studied on the basal (Z–direction) and two prismatic planes (X– and Y–directions) with varying indenter velocities. The investigation of structural evolution is done using atomic displacement analyses to measure the net magnitude of displacement, atomic strain analyses to evaluate the shear strain developed in the process, and Wigner–Seitz defect analyses to calculate the total vacancies at varied timesteps. Furthermore, Voronoi analyses are done when indented on the basal plane to identify the cluster distribution at different planar depths of the specimen. From the analyses, it has been observed that the load-bearing capacity of the specimen varies with the indentation velocity and the direction of indentation on the specimen. Additionally, it is seen that the observed shear and total atomic displacement in the Z–direction is the least in comparison to the other two axes. The partial dislocation 1/3 is seen to be majorly present and the population of dislocation loops is more abundant for lower indenter velocities. Furthermore, clusters and are the major indices developed during nanoindentation on the basal plane where they exhibit symmetrical distribution as observed from the Z–direction
Molecular dynamics simulation-based study of creep–ratcheting behavior of nanocrystalline aluminum
International audienceIn the present study, molecular dynamics simulations have been performed to investigate the creep–ratcheting deformation behavior of nanocrystalline aluminum (NC Al) having an average grain size of ~ 8 nm. The influence of deformation temperature on creep–ratcheting behavior has been studied and associated with underlying mechanisms based on the structural evolution of the material identified. The vacancy concentrations, strains and dislocation densities have been evaluated at the end of each stage of creep–ratcheting process for two ratcheting stress ratios and three different temperatures. In the mean time, the microstructural and defect evolution has been investigated. Accumulation of creep–ratcheting strain is found to increase with the deformation temperature in the range of temperature investigated: 10–467 K. Cyclic hardening dominates in the initial stages of creep–ratcheting, whereas cyclic softening dominates in the final stages at a higher temperature. The creep–ratcheting plots exhibit a primary and steady state regions at room temperature (300 K). In addition, a tertiary region is also perceived at high temperature (467 K). The NC Al specimen is also found to be damaged earlier at a higher temperature (i.e., 467 K) than at 10 K and 300 K. The highest dislocation density is attained for room temperature creep–ratcheting deformation. Finally, it is seen from the dislocation analysis that the Shockley partial and full dislocations are the driving dislocations for the creep–ratcheting deformation process
Molecular Dynamics simulation based investigation of possible enhancement in strength and ductility of nanocrystalline aluminum by CNT reinforcement
International audienceMolecular dynamics (MD) based study of nanocrystalline (NC) Al and CNT (carbon nanotube) reinforced NC Al specimens having grain sizes ~9 nm have been carried out under tensile loading using hybrid potentials for different temperatures (10 K, 300 K and 681 K) at a particular strain rate of 1010 s-1. Structural variation and defect evolution during the deformation have been investigated. An enhancement in both strength and ductility is observed in case of the CNT embedded NC Al specimens with respect to NC Al specimen and such improvement is significant in case of (30,30) CNT embedded NC Al specimen. It is also found that NC Al matrix is fractured first, then the CNT at lower test temperature, whereas at high temperature, the CNT fractures before the matrix