Papers by Keyword: Molecular Dynamic

Abstract: The characteristics of shock wave propagation in aluminum single crystal are simulated by using the molecular dynamics (MD) method based on the embedded atom method (EAM) potential function. The structure of the shock front and the Hugonoit relation are obtained. The simulated results show that a two-wave structure exists in the aluminum single crystal for the particle velocity bellower than 2 km/s and the velocity of the elastic wave increases slightly with the shock loading. While only plastic wave exists in the aluminum single crystal for the particle velocity higher than 2 km/s and the width of the shock front decreases by exponent with the normal stress. The MD simulation results are basically consistent with the experimental results.

Abstract: In this study, the effects of 555-777 defect on Young’s modulus, fracture strength and fracture strain of armchair graphene nanoribbons (AGNRs) and zigzag graphene nanoribbons (ZGNRs) were investigated by using Molecular Dynamics simulations under uniaxial tension. The simulation results show that 555-777 defect significantly reduces the fracture strength and fracture strain of AGNRs and ZGNRs, but has little effect on Young's modulus. The influence of 555-777 defect on the mechanical properties of AGNRs is greater than that of ZGNRs. This study provides a better understanding of mechanical properties of graphene nanoribbons.

Abstract: Interfacial behavior of Al and α-Al₂O₃ are investigated via molecular dynamic simulation (MD) employing reactive force fields parameterized for Al and Al₂O₃. The main result of this work is elucidating the wetting behavior and interface chemistry of molten aluminum on the α-Alumina (0001) surface through MD simulations. Wetting and interface chemistry are studied at 8 different temperatures from 700 to 1400 K for four different droplet sizes: with 16, 24, 32 and 40 Å diameters. Chemical reactions are observed at all temperatures and sizes in addition to diffusion between droplet and substrate atoms into each other during the wetting process. To define the level of wetting, we characterized contact angles of aluminum droplets on alumina substrates for all temperatures and sizes by using a method developed by Hautman and Klein. Chemical reactions are more extensive for the small droplets (16 and 24 Å) due to their larger surface to volume ratio in comparison to the larger droplets (32, and 40 Å) of droplets.

Abstract: We have studied spallation in single crystal of metals under shock at very high strain rate. Our work has been devoted to understanding, and predicting the dynamic ductile damage processes of nucleation, growth and coalescence of voids in these extreme conditions of impact. Recovered sample only indicates final state of damage. Molecular Dynamics calculations are predicting the phenomenon over time. However we need experimental results to validate and improve simulations and models. X-ray tomography analyses are appropriate to extract pore volume distributions. Our study on ductile materials allowed us to conclude that experimental analyses exhibit two power laws attributed to growth and coalescence regimes. Moreover power law is scale invariance so it is possible to compare experiment (macroscopic) to calculation (microscopic). We show that there are good correlations between experimental and Molecular Dynamics pore volume distribution. Thanks X-ray microtomographies findings we progress in understanding the phenomenon of dynamic damage.

Abstract: Crystalline silicon and amorphous silicon are main materials of solar cell. Under prolonged exposure to light, silicon will degrade in quality. Hydrogenation is believed can minimize this degradation by reduce the number of dangling bond. These Molecular dynamics simulations are aimed to elaborate the hydrogenation process of crystalline silicon and amorphous silicon and to elucidate effect of temperature on distribution of hydrogen atoms. Reactive Force Field is selected owing to its capability to describe forming and breaking of atomic bonds as well as charge transfer. Hydrogenation is performed at 300 K, 600 K, 900 K, and 1200 K. Hydrogenated silicon surface hinders further hydrogen atoms to be absorbed such that not all deposited Hydrogen atoms are absorbed by silicon surface. Generally, the higher hydrogenation temperature the more hydrogen atoms are absorbed. Increment of temperature from 900 K to 1200 K only enhances a few numbers of absorbed hydrogen atoms. However, it can enable hydrogen atoms to penetrate into deeper silicon substrate. It is also observed that hydrogen atoms can penetrate into amorphous silicon deeper than into crystalline silicon.