[MatSQ Tip] Module Utilization Tip: LAMMPS (Dislocation) - It's Over 9000!


[MatSQ Tip] Module Utilization Tip: LAMMPS (Dislocation)

2020-07-15 11:41:36
Dislocation is a defect in a crystal in which the arrangement of atoms is displaced due to shear stress.

Dislocation simulation is for evaluating the plasticity and the motion of dislocations. "Dislocation" module enables to calculate the critical resolved shear stress and to evaluate the mobility of a dislocation. You may get the stress-strain curve and the structure variations during shear deformation.

You can perform the dislocation simulation with just a few clicks, by using the "Dislocation" template of the MatSQ LAMMPS module.



1. Modeling

Dislocation shear simulation needs a massive model. So the model is made in the LAMMPS (Dislocation Shear Simulation) module by determining the model size, instead of modeling that directly in the structure builder module.

Therefore, connect the module to the structure builder module, which modeled the orthogonal unit cell, to perform the dislocation shear simulation with LAMMPS (Dislocation Shear Simulation) module.

The following is the model used for the simulation.

  • FCC <110>{111} slip system

  • BCC <110>{110} slip system


Other systems will be added continuously as soon as possible.

The model used for simulation will have the following form.







Edge dislocation

Models should be chosen between edge dislocation and screw dislocation. Both two models can be commonly divided into two parts. 'Fixed layer’ to which stress is applied, and 'Deformation region’ to which is deformed by the applied stress. 'Fixed layer’ is fixed to consider as the suspended region of the experiment. This region is set to a length equal to 10 times of the first nearest distance from the unitcell in the structure builder module. This is kept in mind when using this module.

 

2. Simulation input setting

To perform the dislocation simulation, you should set the input parameters as the following.

  1. Select the appropriate interatomic potential for the system.
    You can check if the potential is suitable for the system you desired to calculate by referring to the DOI.

  2. Select the type of crystal structure of unit cell. (FCC or BCC)

  3. Determine the size of the simulation model.

  4. Select the kind of dislocations. (Edge or Screw)

  5. Set the proper Poisson`s ratio (the metal is normally 0.3).

  6. Determine the displacement to shear direction.

  7. Set the total shear strain.


 

3. Cautions


To obtain appropriate dislocation simulation results, please note the following cautions.

  • Normal direction and glide direction of the dislocation should be moderately long to estimate more accurate results.

  • In the case of the edge dislocation shear simulation, the Z size of the supercell should be at least three times of the unit cell in the z direction.

  • In the case of the screw dislocation shear simulation, the both X and Z size of the supercell should be moderately long to estimate more accurate results.

  • Please note that a lot of charges may be added if the supercell is too large.

  • The calculation times are fast but can be inaccurate if the displacement is too large. Meanwhile, the calculation times are too slow if the displacement is too small.

  • If the total shear strain is small, only the elastic region is calculated. Therefore, the proper total shear strain should be given.



 

 
Need more information?

-Documentation: LAMMPS (Dislocation)

-YouTube: Module Utilization Tip: Edge Dislocation Simulation for Nickel




 

 

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