Reading EBSD Data
To read experimental electron backscatter diffraction (EBSD) data three components are needed
EBSDMesh
Mesh objectEBSDReader
UserObjcetInitial conditions (such as the
ReconVarIC
action provides)
Mesh
The mesh is generated from the EBSD information in the specified EBSD data file to get an optimal reconstruction of the data. This is accomplished in the mesh block using the EBSDMesh
type. The mesh is created with one node per data point in the EBSD data file. If you wish to use mesh adaptivity and allow the mesh to get coarser during the simulation, the uniform_refine
parameter is used to set how many times the mesh can be coarsened. The block takes the form:
[Mesh]
[ebsd_mesh]
type = EBSDMeshGenerator
filename = IN100_120x120.txt
pre_refine = 2
[]
[]
(../moose/modules/phase_field/examples/ebsd_reconstruction/IN100-111grn.i)EBSD Reader UserObject
The UserObject reads in the data file, using the name supplied in the mesh block, and stores a data object with the local data at each material point as well as the average data about each grain. The block syntax is very simple:
[UserObjects]
[ebsd_reader]
type = EBSDReader
[]
[ebsd]
type = PolycrystalEBSD
coloring_algorithm = bt
ebsd_reader = ebsd_reader
enable_var_coloring = true
[]
[grain_tracker]
type = GrainTracker
flood_entity_type = ELEMENTAL
compute_halo_maps = true # For displaying HALO fields
polycrystal_ic_uo = ebsd
[]
[]
[ICs]
[PolycrystalICs]
[PolycrystalColoringIC]
polycrystal_ic_uo = ebsd
[]
[]
[]
(../moose/modules/phase_field/examples/ebsd_reconstruction/IN100-111grn.i)Applying Initial Conditions
The initial condition for the variables is set from the EBSD data. There are three possible use cases summarized below.
Case 1: Create grain structure from the grain numbers in the EBSD data, ignoring the phase number
A grain structure is created from the EBSD data by assigning initial condition values for order parameters. Many more grains can be represented than the number of order parameters. The required blocks are
[Mesh]
# Create a mesh representing the EBSD data
[ebsd_mesh]
type = EBSDMeshGenerator
filename = IN100_001_28x28_Marmot.txt
[]
[]
[GlobalParams]
# Define the number and names of the order parameters used to represent the grains
op_num = 4
var_name_base = gr
[]
[UserObjects]
[ebsd_reader]
# Read in the EBSD data. Uses the filename given in the mesh block.
type = EBSDReader
[]
[ebsd]
type = PolycrystalEBSD
coloring_algorithm = bt
ebsd_reader = ebsd_reader
output_adjacency_matrix = true
[]
[grain_tracker]
type = GrainTracker
# For displaying HALO fields
compute_halo_maps = true
# Link in the ebsd userobject here so that grain tracker can extract info from it
polycrystal_ic_uo = ebsd
[]
[]
[Variables]
[PolycrystalVariables]
# Create all the order parameters
order = FIRST
family = LAGRANGE
[]
[]
[ICs]
[PolycrystalICs]
[PolycrystalColoringIC]
# Uses the data from the user object 'ebsd' to initialize the variables for all the order parameters.
polycrystal_ic_uo = ebsd
[]
[]
[]
(../moose/modules/phase_field/test/tests/reconstruction/1phase_reconstruction.i)Case 2: Initialize a variable from a specific phase number in the EBSD data, ignoring the grain numbers
Here, the value for a single variable is initialized from the EBSD data corresponding to a single phase number. The required blocks are
[Mesh]
# Create a mesh representing the EBSD data
[ebsd_mesh]
type = EBSDMeshGenerator
filename = 'Ti_2Phase_28x28_ebsd.txt'
[]
[]
[UserObjects]
[ebsd]
# Read in the EBSD data. Uses the filename given in the mesh block.
type = EBSDReader
[]
[]
[Variables]
# Creates the two variables being initialized
[c1]
[]
[c2]
[]
[]
[ICs]
[phase1_recon]
# Initializes the variable info from the ebsd data
type = ReconPhaseVarIC
ebsd_reader = ebsd
phase = 1
variable = c1
[]
[phase2_recon]
type = ReconPhaseVarIC
ebsd_reader = ebsd
phase = 2
variable = c2
[]
[]
(../moose/modules/phase_field/test/tests/reconstruction/2phase_reconstruction.i)Case 3: Create an initial grain structure from the EBSD data only corresponding to one phase number Here, the grain and phase numbers are used. The order parameters are initialized from the EBSD data, but only using those grains with a given phase number.
[Mesh]
[ebsd_mesh]
type = EBSDMeshGenerator
filename = Ti_2Phase_28x28_ebsd.txt
[]
[]
[GlobalParams]
op_num = 2
var_name_base = gr
[]
[UserObjects]
[ebsd_reader]
type = EBSDReader
[]
[ebsd]
type = PolycrystalEBSD
coloring_algorithm = bt
ebsd_reader = ebsd_reader
phase = 1
output_adjacency_matrix = true
[]
[]
[Variables]
[PolycrystalVariables]
[]
[]
[ICs]
[PolycrystalICs]
[PolycrystalColoringIC]
# select only data for phase 1 from the EBSD file
polycrystal_ic_uo = ebsd
[]
[]
[]
(../moose/modules/phase_field/test/tests/reconstruction/2phase_reconstruction2.i)Using EBSD Crystal Info
The EBSDReader
local grid data is extracted using the getData(Point)
function call, where you pass in location of the point where you want the data. The available data that can be extracted for a given point is
phi1
- The first Euler anglephi
- The second Euler anglephi2
- The third Euler anglegrain
- The index of the grainphase
- The index of the phasesymmetry
- The symmetry class (from TSL)
An example of using this function is shown here
const EBSDReader::EBSDData & d = _ebsd_reader.getData(p);
_euler_angles(0) = d.phi1;
_euler_angles(1) = d.phi;
_euler_angles(2) = d.phi2;
The EBSDReader average grain data is extracted using the getAvgData(unsigned int)
function call, where you pass in the grain number for which you want the data. The available data that can be extracted
phi1
- The average first Euler anglephi
- The average second Euler anglephi2
- The average third Euler anglephase
- The index of the phase of the grainsymmetry
- The symmetry class (from TSL)p
- Point with centroid location
An example of using this function is show here, taken from ReconVarIC
const EBSDReader::EBSDAvgData & d = _ebsd_reader.getAvgData(grn_index);
_centerpoints[gr] = d.p;
Plotting Color Representation of Crystal Orientations
It is common to use an inverse pole figure representation of the crystal orientations to color the grains to represent EBSD data. To simplify the comparison with experiments, MOOSE has a tool for outputting color values for the inverse pole figure representation that can then be visualized using Paraview. The spatially varying red, green, and blue (RGB) values are outputted as auxvariables that are automatically read by Paraview as a vector.
Two Auxkernels
can be used to output the RGB values. The first, EulerAngleProvider2RGBAux is the simplest but requires the entire domain to have the same crystal structure. The second, EulerAngleVariables2RGBAux requires various other auxvariables that contain the Euler angles, the crystal structure, and the phase number.
The easiest way of outputting the values is to use a custom action block in the input file that is available. The syntax is
[Modules]
[./PhaseField]
[./EulerAngles2RGB]
crystal_structure = cubic
euler_angle_provider = ebsd
grain_tracker = grain_tracker
[../]
[../]
[]
We recommend you plot the colors using Paraview. The EulerAngle2RGB action will create three auxvariables with default names RGB_x
, RGB_y
, and RGB_z
. Paraview will automatically create a vector variable of name RGB_
. To correctly represent the colors,
Select
RGB_
as the visualization variable.In the properties section with the advanced properties toggled on, uncheck
Map Scalars
underScalar Coloring
.