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A quasi-static atomistic simulation method at finite temperature

Bin Liu's picture

Molecular dynamics (MD) method is an important simulation tool, but its results are always doubtful due to its unrealistic high strain rates. In this paper, a hybrid quasi-static atomistic simulation method at finite temperature is developed, which combines the advantages of MD for thermal equilibrium and atomicscale finite element method (AFEM) for efficient equilibration. Some temperature effects are embedded in static AFEM simulation by applying the virtual and equivalent thermal disturbance forces extracted from MD. Alternatively performing MD and AFEM can quickly obtain a series of thermodynamic equilibrium configurations such that a quasistatic process is modeled.

Moreover, a stirring-accelerated MD/AFEM fast relaxation approach is proposed in which the atomic forces and velocities are randomly exchanged to artificially accelerate the “slow processes” such as mechanical wave propagation and thermal diffusion. The efficiency of the proposed methods is demonstrated by numerical examples on single wall carbon nanotubes. The paper can be found at http://dx.doi.org/10.1115/1.4025807

 

Comments

Pu Zhang's picture

Prof Liu,

Do you think it is okay to call the 'equivalent thermal disturbance force' a kind of entropic force? It seems to me that they are close. Thanks.

Bin Liu's picture

Yes. You may call them entropic forces. It's ok to me. But I am not sure physicists have the same opinion.

sir, my general query is whether we need to increase load with time while analysing quasi-static process?

for example for analysing quasi-static crack propagation whether we need to increase load with time to compensate for energy lost in crack cpropagation?

Bin Liu's picture

Dear prerakchitnis,

In reality, many experiments are performing at a very low strain rate or quasi-static loading, such as a tensile test to obtain stress-strain curve. Regarding quasi-static crack propagation, if it is stable crack propagation, you need increase displacement loading to support its propagation.

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