ICME 2017 HW2

From EVOCD
(Difference between revisions)
Jump to: navigation, search
(Added scale categories)
(Part 1 - Single Dislocation Mobility Calculations using MEAM: Filled in walkthrough)
Line 41: Line 41:
  
 
====Step 1====
 
====Step 1====
Generate the atomic structure
+
Generate the atomic structure using [[Atomistic Dislocation Generation]]. Once you have downloaded and compiled the fortran routine, simply run it at the command line as explained on the script page.
 +
For this calculation, you want make an edge dislocation in a PAD geometry. It will create the required data file as atoms.*.edge.pad, where * is either fcc or bcc, depending on your material. You will need to copy the data file to the directory where you will run the MD simulation.
  
 
====Step 2====
 
====Step 2====
Run the LAMMPS Script
+
Edit the LAMMPS input file for your material, applied stress, and desired temperature. These can all be set by variables at the top of the input file.
 +
<pre>
 +
# Variable definitions
 +
variable initTemp equal 300.          # desired temperature
 +
variable sigma equal 15000.    # applied stress in bar
 +
variable material string Ta # material symbol
 +
variable atom_file string atoms.bcc.edge.pad # the configuration was generated by SG with the preprocessor dislocation.f90
 +
</pre>
 +
 
 +
<code>initTemp</code> will determine the temperature of the system.
 +
 
 +
<code>sigma</code> will determine the applied shear stress in bar.
 +
 
 +
<code>material</code> will determine the name of your material used in your MEAM potential files. It expects to find a library file, <code>*.library.meam</code>, and a parameter file, <code>*.meam</code> where the * represents the material symbol.
 +
 
 +
<code>atom_file</code> is the name of the data file that contains the initial atom positions.
  
 
====Step 3====
 
====Step 3====
Run the post-processor and calculate the average dislocation velocity
+
 
 +
LAMMPS will create several output files from the simulation. You can load each of them in [[Ovito]] to see what each includes. You will want to run the post-processing script, [[Single Defect Velocity in Ovitos]], on the <code>dump.shear.unwrap</code> file, following the directions on the script page.
 +
 
 +
It will output a time versus position file which you can use to calculate the velocity of the dislocation.
 +
 
  
 
===Homework Assignment===
 
===Homework Assignment===

Revision as of 11:21, 20 February 2017

< ICME 2017 Overview

Contents

Overview

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

Objective

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.

You can obtain LAMMPS and find the user manual here. Visit the LAMMPS tutorials page for a wide range of examples.

Environment Setup

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.

Calculating Dislocation Velocity

Walkthrough

Step 1

Generate the atomic structure using Atomistic Dislocation Generation. Once you have downloaded and compiled the fortran routine, simply run it at the command line as explained on the script page. For this calculation, you want make an edge dislocation in a PAD geometry. It will create the required data file as atoms.*.edge.pad, where * is either fcc or bcc, depending on your material. You will need to copy the data file to the directory where you will run the MD simulation.

Step 2

Edit the LAMMPS input file for your material, applied stress, and desired temperature. These can all be set by variables at the top of the input file.

# Variable definitions
variable initTemp equal 300.          	# desired temperature
variable sigma equal 15000.    		# applied stress in bar
variable material string Ta		# material symbol
variable atom_file string atoms.bcc.edge.pad # the configuration was generated by SG with the preprocessor dislocation.f90

initTemp will determine the temperature of the system.

sigma will determine the applied shear stress in bar.

material will determine the name of your material used in your MEAM potential files. It expects to find a library file, *.library.meam, and a parameter file, *.meam where the * represents the material symbol.

atom_file is the name of the data file that contains the initial atom positions.

Step 3

LAMMPS will create several output files from the simulation. You can load each of them in Ovito to see what each includes. You will want to run the post-processing script, Single Defect Velocity in Ovitos, on the dump.shear.unwrap file, following the directions on the script page.

It will output a time versus position file which you can use to calculate the velocity of the dislocation.


Homework Assignment

  1. 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.
  2. Run LAMMPS using the atom positions file generated in the previous step along with the LAMMPS input file for each of the following:
    1. Show the atom positions before the calculation illustrating the dislocation by looking at the dump.equilibration file.
    2. 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.
    3. 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.
    4. Determine the drag coefficient using Equation 9.2 in the ICME for Metals textbook from the study in Part (c).
Dislocation Mobility

Part 2 - Dislocation Dynamics

Objective

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.

Environment Setup

Source code and example inputs can be downloaded from this link.
Post processing instructions for MDDP are found here.

Simulating the Motion of a Dislocation

Walkthrough

Step 1

Edit datain and create the geometry input file

Step 2

Edit DDinput for your material parameters and mobility

Step 3

Run MDDP

Step 4

Post-process using TecPlot or (hopefully) Ensight or Paraview

Homework Assignment

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.

Additional Guides

ICME 2012 HW2

ICME 2013 HW2

ICME 2015 HW2

LAMMPS tutorials

MDDP Post Processing

License

By using the codes provided here you accept the the Mississippi State University's license agreement. Please read the agreement carefully before usage.

Personal tools
Namespaces

Variants
Actions
home
Materials
Material Models
Design
Resources
Projects
Education
Toolbox