Simulations of surface stress effects in nanoscale single crystals

Abstract

Onset of vacuum arcing near a metal surface is often associated with nanoscale asperities, which may dynamically appear due to different processes ongoing in the surface and subsurface layers in the presence of high electric fields. Thermally activated processes, as well as plastic deformation caused by tensile stress due to an applied electric field, are usually not accessible by atomistic simulations because of long time needed for these processes to occur. On the other hand, finite element methods, able to describe the process of plastic deformations in materials at realistic stresses, do not include surface properties. The latter are particularly important for the problems where the surface plays crucial role in the studied process, as for instance, in case of plastic deformations at a nanovoid. In the current study by means of molecular dynamics and finite element simulations we analyse the stress distribution in single crystal copper containing a nanovoid buried deep under the surface. We have developed a methodology to incorporate the surface effects into the solid mechanics framework by utilizing elastic properties of crystals, pre-calculated using molecular dynamic simulations. The method leads to computationally efficient stress calculations and can be easily implemented in commercially available finite element software, making it an attractive analysis tool.

In situ resistivity measurement of metal surfaces to track down dislocations caused by high field conditioning

“…In recent years, theoretical models and simulations were presented supporting the hypothesis of intrinsic process connected with the changes under surface [13,14]. These are thermally activated processes, initiated by electron field emission, accompanying the plastic deformation caused by tensile stress due to an applied electric field [15,16].…”

Irregular and suppressed elastic deformation by a structural twist in cellulose nanofibre models

“…The torsion-derived mechanical properties have rarely been considered because previous all-atom MD simulations could only treat very small crystal models with an upper length limit of ~ 50 nm owing to balancing issues of the computational load and accuracy of the intermolecular interactions [23][24][25][26] . In addition, there is an inherent disadvantage in all-atom MD-based mechanics calculations that the obtained data are not unique because of the vague definition of the atomic cross-sectional area 27 . Therefore, it is still a great challenge to separately consider the twisting mechanism and the mechanical characteristics derived from the twisted structure based on cellulose crystals.…”