In this project, you will use discrete dislocation dynamics simulation to examine the increase in dislocation density in an Al sample, starting from a single Frank-Read source. You will examine the effect of (1) cross-slip, (2) the applied stress, and (3) the dislocation mobility parameters on the increase in dislocation density in a periodic simulation. This will allow you to examine how to provide information for higher length scale models, such as the density evolution equation you considered in Module 1.
You will produce a short report documenting your findings. Your
report should contain a separate section for each of the tasks listed
below, and provide the explicit deliverables requested for each task
indicated by [Report] below. For the input scripts
below, simply cut-and-paste your input script into your report. Your
report should be formatted as a single pdf document comprising your
report. You may wish to write your report in latex and convert using
pdflatex, or in markdown and convert using
pandoc report.text --to latex --out report.pdf;
alternatively, you can put together a clearly formatted jupyter
notebook. (module load pandoc and
module load texlive to have the most up-to-date versions of
each).
You should submit your report by creating a subdirectory called
/class/mse404pla/sp22/<your_net_id>/Project3
and copying your PDF into that directory by 11:59pm on 2 May
2022. Late submissions will not be accepted; let me know in advance if
you will have difficulty with completion..
You will use ParaDiS throughout for your simulations.
These codes are freely available (after signup) from the ParaDiS website; there are
copies of these on the EWS linux workstations, including the compiled
versions of the ParaDiS executables. There is also
documentation for both available on EWS in the
/class/mse404pla/ParaDiS/doc directory. The directories of
interest are:
ParaDiS and DDLab:
/class/mse404pla/ParaDiS/doc/class/mse404pla/ParaDiS/2.5.1The steps you will take below are:
In the directory /class/mse404pla/ParaDiS/Project you
will find a starting control file and node file. Copy these to an
appropriate subdirectory in your home directory. You will likely want to
use a similar directory structure to what we used in the
walkthrough.
NOTE: For this assignment, you will be running
multiple dislocation dynamics simulations. If you use the same
output directory for each run, ParaDiS will
append the output of the current run to whatever is already
there. This allows ParaDiS to “restart” a previous run,
continuing from where it left off. This is not the behavior you
will be interested in so either (a) make different output
directories for each run, or (b) copy out what files you need to an
appropriate place after running.
First, look through the control file. You will need to make a few edits to this to begin.
### This is the control file for the FCC Al Frank-Read source
# Output generated by this example will be placed under the directory
# specified by the <dirname> value and includes:
# restart files
# various properties files
dirname = "Output/"
# Domain geometry
numXdoms = 1
numYdoms = 1
numZdoms = 1
# Cell geometry
numXcells = 3
numYcells = 3
numZcells = 3
# Boundary type
xBoundType = 0
yBoundType = 0
zBoundType = 0
# Dynamic load balancing
decompType = 1
DLBfreq = 0
# Discretization and topological change controls
maxSeg = 400
minSeg = 20
remeshRule = 3
enforceGlidePlanes = 1
splitMultiNodeFreq = 1
# Simulation time and timestepping controls
maxstep = 200000
timestepIntegrator = "trapezoid"
nextDT = 1.0e-10;
rTol = 2.5
rmax = 5
rc = 5.0
# Fast Multipole Method controls
Rijmfile = "inputs/Rijm.cube.out"
RijmPBCfile = "inputs/RijmPBC.cube.out"
# fmEnabled = 1
# fmEnabled = 1
# fmMPOrder = 2
# fmTaylorOrder = 5
# fmCorrectionTbl = "inputs/fm-ctab.Al.m2.t5.dat"
# Loading conditions
loadType = 0
appliedStress = [ 0, 0, 100e6, 0, 0, 0 ]
# Material and mobility parameters
mobilityLaw = "FCC_0b"
shearModulus = 27e9 # Voigt Average
pois = 0.333
burgMag = 2.86e-10
# Mobility law and cross-slip
MobScrew = 60.000000e+04
MobEdge = 60.000000e+04
enableCrossSlip = 1
# I/O controls and parameters
#
savecn = 1
savecnfreq = 2000
saveprop = 1
savepropfreq = 100
savetimers = 0The dirname will need to be changed to the directory you
want to use. In addition, note the parameters that describe the loading
(constant stress, corresponding to a “creep” simulation), mobilities,
and the enabling of cross-slip. Also take note of the parameters that
control the number of steps, and how often information (restart files
and material properties) are stored. You may want to change these as
your simulations progress.
Turn cross-slip back on. Proceed through a number of simulations, going a \(z\) normal stress from 50 MPa to 150 MPa in steps of 25 MPa.
[Report] For each, make a plot of dislocation density with plastic strain. Try to reach 1% strain. What do you notice for the dislocation density with increasing stress?
[Report] For each stress, take a few snapshots (hit the F10 key to generate a postscript file in the X-window) to show example dislocation configurations. Discuss what types of dislocation configurations you see (junctions, loops, superjogs).
[Report] Is there a non-zero stress where the dislocation density does not grow? Explain.