Molecular Dynamics Study of Bulk Properties of Polycrystalline NiTi

Molecular dynamics (MD) simulations were carried out to study the bulk polycrystalline properties of NiTi. Thermally driven phase transitions of NiTi between martensite and austenitewere simulated using single crystalline simulation domains. With external stress boundary conditions, MD simulation successfully predicted experimentally observed phase transformation temperatures of bulk polycrystalline. Elastic characteristics of NiTi martensite were simulated using polycrystalline simulation domains that consist of realistic disorientations and grain boundary structures. The existence of grain disorientation and grain boundary lowered the potential energy of the simulation domain, which led to more realistic elastic modulus prediction. Analysis of simulation domains that predicted realistic bulk polycrystalline properties showed that the major difference between single crystalline and polycrystalline structures is atomic stress distribution.

Fatigue crack growth characteristics of Fe and Ni under cyclic loading using a quasi-continuum method

A quasi-continuum (QC) method based on the embedded atom method (EAM) potential was employed to investigate the fatigue crack growth and expansion characteristics of single-crystal Fe and Ni under cyclic loading modes I and II. In particular, the crack growth and expansion characteristics of Fe and Ni under cyclic loading were evaluated in terms of atomic stress fields and force–distance curves. The simulation results indicated that under cyclic loading, the initially damaged area of the crack will coalesce again after compression or shear to the initial geometry leading to a strengthening of the material. If no coalescence appears, the crack spreads rapidly and the material breaks. Moreover, under the cyclic loading of shear at any orientation, the slip dislocation observed in the materials considerably affects the release of stress.

An ISODATA Approach to the Estimation of Atomistic Definition for Continuum Stress

The atomic stress tensor at a given continuum point is a spatial average value of some volume near the point. Recent progresses in multiscale modeling include the dealing of the optimal number and the size of these volumes. In this paper, we motivate the application of Iterative self-organizing data analysis technique algorithm to estimate volume numbers. The size of these space averaging volumes then could be got using Gaussian mixture model. Reduced computation complexity is offered by this method. Atomistic simulations are conducted to analyze the stress of a stone-wales defect graphene sheet to validate the method. Other multiscale values could also be determined using this method.

Graphene mechanics: II. Atomic stress distribution during indentation until rupture

Using the Time-Resolved Force Distribution Analysis, we find a high stress concentration in the graphene sheet under the indenter tip, while the rest of the sheet remains at background stress levels.

Influence of Ageing on Surface Quality of Machined Nanostructures

A three-dimensional model of Monte Carlo (MC) simulation is proposed to study the effects of ageing on the surface quality of machined nanostructures. The model includes the utilization of the Morse potential function to simulate the interatomic force between the atoms in workpieces. The results show that the ageing processes have important influence on the surface morphology and internal structure of machined workpiece. Most of the disordered point defects and one large stacking fault structures in machined workpiece disappear after ageing, but still some defect structures remain. In addition, distribution of atomic potential and atomic stress in the workpiece become regular in the aging process, and the atoms of the defect structures have much higher potential energy and stress. Finally, surface roughness of machined workpiece definitely increases after ageing. To analyze the morphology of machined surface after ageing is very practical and meaningful.