ICME 2017 HW2
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Revision as of 10:50, 20 February 2017
In this homework, we will bridge information from the nanoscale to the microscale by calculating the dislocation mobility drag coefficient using Molecular Dynamics, and using it to run Dislocation Dynamics simulations. There are two parts to this homework,
- Molecular Dynamics (MD) using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS)
- Dislocation Dynamics (DD) using Multiscale Dislocation Dynamics Plasticity (MDDP)
All necessary input files and scripts are provided here or in /scratch/ICME_2017/Homework2/ . Move any of these files to your own directory (and make a backup copy) before trying to perform any simulations.
Use /scratch/"Your Directory" for best results, especially if your job reads/writes much data.
Write a full report that follows a journal article manuscript format (include figures and tables in the text).
Upon completion, submit a .pdf and .doc(x) file of your report. Be sure to also include the requested files and plots from each section of the homework.
Part 1 - Single Dislocation Mobility Calculations using MEAM
For this section, you will use the Modified Embedded Atom Method (MEAM) in Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to acquire the dislocation mobility drag coefficient for your material.
LAMMPS is an open source code and can be downloaded here. The source code can be easily compiled, or binary distributions are available for easy installation.
In addition to the software, you will need an input file, an atom position file, a post-processing script, and two files for your atomistic potential.
- The input file for this simulation is DislocationVelocity.
- The atom position file will be created by Atomistic Dislocation Generation.
- The post-processing script uses Ovito's scripting and analysis capabilities: Single Defect Velocity in Ovitos.
- The atomistic potential files will be from ICME 2017 HW1.
Calculating Dislocation Velocity
Generate the atomic structure
Run the LAMMPS Script
Run the post-processor and calculate the average dislocation velocity
- Generate the atom positions file to be used for studying the mobility of an edge dislocation for your FCC or BCC material. A unit cell size of 100 x 60 x 2 will produce a simulation box containing ~70,000 atoms for an FCC structure.
- Run LAMMPS using the atom positions file generated in the previous step along with the LAMMPS input file for each of the following:
- Show the atom positions before the calculation illustrating the dislocation by looking at the dump.equilibration file.
- Use a minimum of three (3) different MEAM parameter sets based on the sensitivity analysis from HW1. Compare the position vs. time curves for each set.
- Study the effects of the applied shear stress on the dislocation velocity in your material compared to aluminum as in Figure 9.7 (a) in the ICME for Metals textbook.
- Determine the drag coefficient using Equation 9.2 in the ICME for Metals textbook from the study in Part (c).
Part 2 - Dislocation Dynamics
In this section, you will use Multiscale Dislocation Dynamics Plasticity (MDDP) to simulate the motion of a dislocation, thereby upscaling the dislocation mobility from the nanoscale.
Simulating the Motion of a Dislocation
Edit datain and create the geometry input file
Edit DDinput for your material parameters and mobility
Post-process using TecPlot or (hopefully) Ensight or Paraview
1. Run MDDP using the single Frank-Read source (SFRS) input. Be sure to change the data file to reflect the properties of your material as determined from LAMMPS.
- a. Generate stress-strain curves using a minimum of three (3) different mobilities.
- b. Illustrate the SFRS at several intervals as the dislocation loop propagates.
2. Run MDDP using the multiple Frank-Read sources (MFRS) input. Be sure to change the data file to reflect the properties of your material as determined from LAMMPS.
- a. Generate stress-strain curves using a minimum of three (3) different mobilities. These will be used for upscaling to crystal plasticity.
- b. Illustrate the MFRS at several intervals as the dislocation loops propagate.
|Frank Read Source Operation|
Part 3 - Room for Improvement
Improve the instructions and/or tutorials for running LAMMPS/MDDP using your experience gained from Parts 1 and 2.
By using the codes provided here you accept the the Mississippi State University's license agreement. Please read the agreement carefully before usage.