ANSYS
Tutorial
Version 7
Fracture Analysis Consultants, Inc
www.fracanalysis.com
Revised: July 2016
Table of Contents:
1.0 Introduction .......................................................................................................................... 6
2.0 Tutorial 1: Crack Insertion and Growth in a Cube .............................................................. 6
2.1 Step 1: Create the ANSYS FE Model ............................................................................. 6
2.2
Step 2: Reading ANSYS FE Model into FRANC3D ...................................................... 8
Step 2.1: Importing ANSYS FE Model .................................................................................. 8
Step 2.2: Select the Retained Items in the FE Model ........................................................... 10
Step 2.3: Displaying the FE Model ....................................................................................... 12
2.3
Step 3: Importing as a Sub-Model ................................................................................... 13
2.4
Step 4: Insert a Crack ..................................................................................................... 18
Step 4.1: Define a new Crack from FRANC3D Menu ......................................................... 18
Step 4.2: Insert Cracks from Files......................................................................................... 23
2.5
Step 5: Static Crack Analysis ........................................................................................ 26
Step 5.1: Select Static Crack Analysis .................................................................................. 26
Step 5.2: Select FE Solver .................................................................................................... 27
Step 5.3: Select ANSYS Analysis Options ........................................................................... 28
2.6
Step 6: Compute Stress Intensity Factors ...................................................................... 30
Step 6.1: Select Compute SIFs.............................................................................................. 30
2.7
Step 7: Manual Crack Growth ....................................................................................... 31
Step 7.1: Select Grow Crack ................................................................................................. 32
Step 7.2: Specify Growth Rate.............................................................................................. 33
Step 7.3: Specify Fitting and Extrapolation .......................................................................... 33
Step 7.4: Specify Crack Front Template ............................................................................... 35
2.8
Step 8: Automatic Crack Growth .................................................................................. 36
Step 8.1: Open FRANC3D Restart File ................................................................................ 36
Step 8.2: Select Crack Growth Analysis ............................................................................... 36
Step 8.3: Specify Growth Parameters ................................................................................... 37
Step 8.4: Specify Growth Model Data .................................................................................. 38
Step 8.5: Specify Fitting and Template Parameters .............................................................. 39
Step 8.6: Specify Extension or Cycle Data ........................................................................... 40
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Step 8.7: Specify Analysis Code ........................................................................................... 41
Step 8.8: Specify Analysis Options ...................................................................................... 42
2.9
Step 9: SIF History and Fatigue Life ............................................................................ 44
Step 9.1: Select SIFs Along a Path ....................................................................................... 44
Step 9.2: Select SIFs For All Fronts ..................................................................................... 45
Step 9.3: Select Fatigue Life Predictions .............................................................................. 46
3.0 Tutorial 2: Multiple Load Cases plus Crack Face Tractions ............................................. 51
3.1 Step 1: Reading ANSYS FE Model into FRANC3D .................................................... 52
Step 1.1: Importing ANSYS FE Model ................................................................................ 52
Step 1.2: Select the Retained Items in the FE Model ........................................................... 55
Step 1.3: Displaying the FE Model ....................................................................................... 57
3.2
Step 2: Insert Crack From File ...................................................................................... 57
3.3
Step 3: Apply Crack Surface Traction .......................................................................... 60
3.4
Step 4: Static Analysis................................................................................................... 62
Step 4.1: Run ANSYS static crack analysis.......................................................................... 62
Step 4.2: Compute SIFs ........................................................................................................ 64
Step 4.3: Re-Run ANSYS static crack analysis with crack face contact .............................. 66
Step 4.4: Compute SIFs with crack face contact .................................................................. 68
3.5
Step 5: Apply Surface Treatment Residual Stress ........................................................ 71
3.6
Step 6: Apply Tractions from Mesh-Based Stress ........................................................ 77
Step 6.1: Create Mesh-Based Stress Field ............................................................................ 77
Step 6.2: Apply Mesh-Based Stress as Crack Face Traction ................................................ 79
4.0 Tutorial 3: Two Cubes Glued Together ............................................................................ 83
4.1 Step 1: Create the ANSYS FE Model ........................................................................... 83
4.2
Step 2: Import ANSYS FE Model into FRANC3D ...................................................... 85
Step 2.1: Importing ANSYS FE Model ................................................................................ 85
Step 2.2: Insert a Crack ......................................................................................................... 86
Step 2.3: Static Crack Analysis ............................................................................................. 88
Step 2.4: Compute SIFs ........................................................................................................ 88
Step 2.5: Plot Deformed Shape ............................................................................................. 88
Step 2.6: Contact surface mesh not retained ......................................................................... 89
Step 2.7: Specify No Crack Material Region........................................................................ 91
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5.0 Tutorial 4: Disk with Rotation and Temperature .............................................................. 92
5.1 Step 1: Create the ANSYS Disk Model ........................................................................ 92
5.2
Step 2: Run ANSYS Thermal Analysis ........................................................................ 94
5.3
Step 3: Run ANSYS Structural Analysis ...................................................................... 95
5.4
Step 4: Import Disk into FRANC3D ............................................................................. 96
5.5
Step 5: Insert Initial Crack ............................................................................................ 97
5.6
Step 6: Static Crack Analysis ........................................................................................ 99
5.6
Step 6: Compute SIFs .................................................................................................. 101
5.7
Step 7: Crack Growth .................................................................................................. 103
5.8
Step 8: Automatic Crack Growth ................................................................................ 106
5.9
Step 9: Analysis Results .............................................................................................. 108
6.0 Tutorial 5: Multiple Cracks in a Plate ............................................................................. 111
6.1 Step 1: Create the ANSYS Plate Model ...................................................................... 111
6.2
Step 2: Import Plate Model into FRANC3D ............................................................... 112
6.3
Step 3: Insert Multiple Cracks ..................................................................................... 114
6.4
Step 4: Static Crack Analysis ...................................................................................... 124
6.5
Step 5: Compute SIFs for Multiple Crack Fronts ....................................................... 126
6.6
Step 6: Grow Multiple Cracks ..................................................................................... 126
6.7
Step 7: Grow Crack around a Corner .......................................................................... 129
6.8
Step 8: Grow Crack through a Back Surface .............................................................. 134
7.0 Tutorial 6: Computing Fatigue Life Cycles .................................................................... 138
7.1 Step 1: Perform Crack Growth .................................................................................... 141
7.2
Step 2: Compute Fatigue Crack Growth Cycles ......................................................... 143
7.3
Step 3: Crack Growth and Fatigue Options ................................................................ 145
7.3.1 Variable Amplitude Loading ..................................................................................... 147
7.3.2 Spectrum Loading for Manu Model .......................................................................... 148
7.4
Step 3: Sequence Crack Growth ................................................................................. 150
7.5
Step 4: Spectrum Crack Growth ................................................................................. 150
7.6
Step 5: Transient Crack Growth .................................................................................. 150
8.0 Tutorial 7: Resume Growth with Larger Submodel ....................................................... 151
8.1 Step 1: Extract and Save Crack Geometry .................................................................. 151
8.2
Step 2: Restart from Saved Crack Geometry .............................................................. 152
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8.3
Step 3: Combine SIF Histories .................................................................................... 157
9.0 Tutorial 8: Fretting Fatigue ............................................................................................. 164
9.1 Step 1: Saving ANSYS Data ....................................................................................... 164
9.2
Step 2: Fretting Model Import..................................................................................... 166
9.3
Step 3: Fretting Crack Nucleation ............................................................................... 169
9.3
Step 3: Discrete Crack Nucleation .............................................................................. 173
10.0 Tutorial 9: Multiple Submodel Portions ......................................................................... 181
10.1
Step 1: Import Plate Model into FRANC3D ........................................................... 182
10.2
Step 2: Insert Multiple Cracks ................................................................................. 185
10.3
Step 3: Crack Analysis ............................................................................................ 190
11.0 Tutorial 10: Session Log Playback ................................................................................. 192
12.0 Tutorial 11: Python Interface .......................................................................................... 195
13.0 Tutorial 12: ANSYS Workbench .................................................................................... 197
5
1.0 Introduction
This manual contains tutorials that introduce the fracture simulation capabilities of FRANC3D
Version 7 and ANSYS Version 15 (other versions should work). The FRANC3D software is
introduced by first analyzing a simple surface crack in a cube. Subsequent tutorial examples
build on this first example and describe additional capabilities and features of the software. It is
intended that the user perform the operations as they are presented, but you should feel free to
experiment, and you should consult the other reference documentation whenever necessary.
Menu and dialog box button selections are indicated by bold text, such as File. Window regions
and dialog options, fields and labels will be underlined. Model names and file names will be
indicated by italic text.
2.0 Tutorial 1: Crack Insertion and Growth in a Cube
The first tutorial simulates a surface crack in a cube under far-field tension. It is assumed that
the user is familiar with a pre-processor for ANSYS; we use ANSYS Mechanical APDL. Once
the model is created, the FRANC3D steps necessary to read the mesh information, insert a crack,
rebuild the mesh, perform the ANSYS analysis, and compute stress intensity factors are all
described.
2.1
Step 1: Create the ANSYS FE Model
First, create a cube model using any pre-processor for ANSYS. Here we simply outline the
necessary steps to create the model and boundary conditions to ensure that we have a complete
model that we can use with FRANC3D.
1. Create a 10x10x10 cube geometry; assume units of length are mm.
2. Subdivide the edges for meshing using 10 to 20 subdivisions.
3. Define the element type as quadratic elements; use brick or tetrahedral elements.
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4. Define the material properties as 10000 for the elastic modulus and 0.3 for the Poisson’s
ratio; assume the units for E are MPa.
5. Mesh the volume.
6. Boundary conditions will consist of displacement constraints on the bottom surface and
uniform traction (a negative pressure) on the top surface of 10 MPa. The bottom surface
is constrained in the y-direction, the bottom left edge is also constrained in the xdirection, and the point at the origin is also constrained in the z-direction.
7. Save the model as a .cdb file (Ansys_Cube.cdb). When writing the .cdb file, use
“cdwrite,DB,file_name,cdb”; do not include the IGES data.
The resulting model should appear as in Fig 2.1. The symbols for the boundary conditions are
displayed attached to the mesh model.
Figure 2.1: ANSYS cube with brick element mesh and boundary conditions.
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2.2
Step 2: Reading ANSYS FE Model into FRANC3D
Start by importing an existing volume element mesh into FRANC3D. We use the model written
in the previous step.
Now you can choose to do either Step 2 or Step 3 (Section 2.3); we describe both Steps here, but
we use Step 3 for subsequent steps of this tutorial.
Step 2.1: Importing ANSYS FE Model
Start with the FRANC3D graphical user interface, Fig 2.2, and select File and Import. In the
window shown in Fig 2.3, choose Complete Model. Switch the Mesh File Type radio button in
the Select Import Mesh File window, Fig 2.3, to ANSYS, and select the file name for the model,
called Ansys_Cube.cdb here, Fig, 2.4. Select Next.
Figure 2.2: FRANC3D graphical user interface
8
Figure 2.3 Import type
Figure 2.4: Select Input Mesh File dialog box
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Step 2.2: Select the Retained Items in the FE Model
The next panel, Fig. 2.5, allows you to choose the mesh surface facets that are retained from the
ANSYS .cdb file. Surfaces with boundary conditions appear in blue as shown in Fig 2.6, and
turn red when selected, Fig 2.7. We retain the surfaces with boundary conditions (top and
bottom of the cube) by choosing Select All. The boundary conditions are transferred
automatically to the new mesh when a crack is inserted. Select Finish.
Figure 2.5: Select Retained BC Surfaces wizard panel.
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Figure 2.6: ANSYS Model retain BC Surfaces wizard panel.
Figure 2.7: ANSYS Model retain BC Surfaces wizard panel.
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Surface Mesh NOT Retained
Note that the surface mesh facets do not have to be retained, and if a crack will be inserted into a
surface that has boundary conditions, then the surface mesh must not be retained. In such a case,
the boundary condition data is transferred to the remeshed surface. In practice, transfer of
boundary condition data is simpler and more precise if the surface mesh can be retained, but
sometimes this is not possible and FRANC3D will automatically map the boundary condition
data to the new mesh.
Step 2.3: Displaying the FE Model
The model is displayed in the FRANC3D modeling window (with Markers turned off). You can
turn on the surface mesh, or manipulate the model view by rotating, etc. The model should
appear as in Fig 2.8, which shows that the mesh is retained on the top surface (as well as the
bottom surface that is not shown) where the boundary conditions are applied.
Figure 2.8: ANSYS model imported into FRANC3D, showing retained facets on the pressure
surface at the top of the cube.
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2.3 Step 3: Importing as a Sub-Model
If you chose to do Step 2 above, either skip this step, or close the current model using the File Close menu before starting this step.
The ANSYS model can be split into smaller parts before inserting the crack. Go to File and
Import, and choose the Import and divide into global and local models radio button shown in
Fig 2.9, and choose the Ansys_Cube.cdb model, Fig. 2.10, as before. Remember to set the Mesh
File Type radio button.
Fig 2.9: Import options
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Figure 2.10: Select Input Mesh File selection.
This time, instead of the retain BC surfaces window in Fig 2.5, the Define a Local Submodel
window shown in Fig 2.11 appears. Figures 2.12 and 2.13 show two of the selection tools.
Selections are made using the tools; elements to be retained appear red, and the selection is
confirmed with the Crop button. The Rubberband Box tool is used, as shown in Fig 2.14, to
create a smaller portion of the cube that still has an exposed face for crack insertion.
14
Figure 2.11: Define a Local Submodel Window
Figure 2.12: Plane Cutting tool
15
Figure 2.13: Element-by-Element un-selection
We are inserting a surface crack normal to the y-axis (loading direction) and located on the +z
surface, and the selection in Fig 2.14 is designed for this.
Figure 2.14: Rubberband Box selection tool
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Once the elements have been selected and cropped, select Next. The Save the Files window
appears, Fig 2.15. Choose the names of the local and global models and their location; we use
the default file names. Select Next.
Figure 2.15: Local/Global model save window
If the local cropped model has a surface with boundary conditions, then the Select Retained BC
Surfaces window from Fig 2.5 appears. Otherwise, the local model appears in the FRANC3D
main window, with retained surfaces wherever the local and global models connect (the cut
surfaces).
In this case, the cropped selection in Fig 2.14 avoids all surfaces with boundary conditions.
However, if there are ANSYS node components in the local model, then the Select Retained BC
Surfaces window will be displayed. In this case, just select Finish and the local model is
displayed in the FRANC3D main window, Fig 2.16.
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Figure 2.16: Local model with retained mesh facets on cut-surface
2.4
Step 4: Insert a Crack
We now insert a half-penny surface crack into the model. The local submodel from Section 2.3 is
used, as opposed to the full model. In Step 4.1, we describe how to define a new crack, and in
Step 4.2, we describe how to insert a flaw from a file.
Note that you should not try to re-insert a crack into a cracked model. Step 4.2 will be used in
subsequent tutorials, but is described here.
Step 4.1: Define a new Crack from FRANC3D Menu
From the FRANC3D menu, select Cracks and New Flaw Wizard, Fig 2.17. The first panel of
the wizard should appear as in Fig 2.18. The flaw being added is a crack with zero volume. We
select the Save to file and add flaw radio button to save the file for future analyses. Select Next.
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The second panel of the wizard, Fig 2.19, lets you choose the crack shape; the ellipse is the
default and is what we want in this case. Select Next.
Figure 2.17: New Flaw Wizard menu item selected.
Figure 2.18: New Flaw Wizard first panel – choose Crack (zero volume flaw).
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Figure 2.19: New Flaw Wizard second panel – choose ellipse library shape.
The crack is a circle with radius=1, centered on the cube’s front (+z) face, and parallel to the xzplane (normal to y). The third wizard panel lets you set the a and b parameters for the ellipse,
Fig 2.20; set a=1 and b=1. Select Next.
Figure 2.20: New Flaw Wizard third panel – set ellipse dimensions.
20
The fourth panel lets you set the crack location and orientation, Fig 2.21. We place the crack at
the center of the front face at coordinates (5,5,10) and we rotate the crack 90 degrees about the xaxis. Select Next.
Figure 2.21: New Flaw Wizard fourth panel – set crack location and orientation.
The final panel allows you to set the crack front mesh template parameters, Fig 2.22. We use the
defaults; the default template radius is based on the crack dimensions and might need to be
adjusted depending on the model and crack. Select Finish. At this point, you are asked to
specify the file name to save the crack information, Fig 2.23; we call it Cube_Crack.crk. Select
Accept.
21
Figure 2.22: New Flaw Wizard final panel – set template mesh parameters.
Figure 2.23: New Flaw Wizard final panel – set template mesh parameters.
The crack is inserted into the model and then remeshing occurs. A Flaw Insertion Status window
is displayed during this process, Fig 2.24. There are four stages: geometric intersection of the
crack with the model, surface meshing, volume meshing, and smoothing of the mesh to produce
better quality elements. The final result should appear as in Fig 2.25, with the surface Mesh
turned on.
22
Figure 2.24: Flaw Insertion Status window.
Figure 2.25: Remeshed cracked local model.
Step 4.2: Insert Cracks from Files
Note that you should not do this step if you have already inserted the crack into the model in
Step 4.1. If you want to try this step, you must close the model from Step 4.1 and re-import the
original uncracked model.
23
From the FRANC3D menu, select Cracks and Flaw From Files, Fig 2.26. The first panel of the
wizard should appear as in Fig 2.27. Choose the Cube_Crack.crk file and hit Accept. The flaw
being added is a circle with radius=1, centered on the cube’s front face, and parallel to the xzplane. This crack was created using the New Flaw Wizard and the save to file option in Step 4.1.
Figure 2.26: Flaw From Files option in Crack menu.
24
Figure 2.27: Flaw from file dialog to select .crk file.
The next panel of the wizard, Fig 2.18, allows you to adjust the location of the flaw. The
orientation cannot be changed. The final panel, Fig 2.29, allows you to set the template mesh.
Figure 2.28: Flaw wizard panel to set location.
25
Figure 2.29: Flaw geometry shown in the model with crack template mesh
2.5
Step 5: Static Crack Analysis
Once the crack is inserted and remeshed, we must perform the stress analysis using ANSYS,
which will provide the displacement results that are needed to compute stress intensity factors.
Typically you should run a “static crack analysis” of the initial crack prior to running automated
crack growth; this allows you to verify that the simulation is valid. You might also do a level of
template mesh refinement to verify that the computed SIFs are accurate.
Step 5.1: Select Static Crack Analysis
From the FRANC3D menu, select Analysis and Static Crack Analysis. The first panel of the
wizard should appear as in Fig 2.30. We specify the file name for the FRANC3D database first.
We call it Ansys_Cube_Subdivide.fdb here; select Next once you enter a File Name. Note that
you cannot use the initial uncracked Ansys_Cube.cdb or Ansys_Cube_LOCAL.cdb file, as a new
.cdb will be created and saved during the analysis, and the original uncracked .cdb files are
reused for each step of crack growth.
26
Figure 2.30: Static Analysis wizard first panel – File Name
Step 5.2: Select FE Solver
The next panel of the wizard, Fig 2.31, allows you to specify the solver; choose ANSYS and
select Next (button not shown in Fig 2.31).
Figure 2.31: Static Analysis wizard second panel – choose solver
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Step 5.3: Select ANSYS Analysis Options
The next panel of the wizard, Fig 2.32, allows you to specify the ANSYS output and analysis
options. The model is a sub-model and needs to be connected with the global model, so the
Connect to global model box should automatically be checked if the FRANC3D submodeler tool
was used. The next panel, Fig 2.33, allows you to set the local + global model connection.
Note that if the model being analyzed is a full/complete model, the panel in Fig 2.32 is the final
panel as there is no global model.
Figure 2.32: Static Analysis wizard third panel – ANSYS output options
28
The panel in Fig 2.33 shows the options for tying together the local and global models.
AUTO_CUT_SURF and GLOBAL_CONNECT_SURF are the sets/surfaces created by the
FRANC3D submodeling tool and should be selected automatically. Click Finish to start ANSYS
running (in batch/background mode). FRANC3D writes files and then attempts to execute
ANSYS based on the ANSYS Executable information, Fig 2.32. You can monitor the
FRANC3D CMD window and the ANSYS log files for errors or messages.
Choosing Write files but DO NOT run analysis will create all the necessary files if the analysis
needs to be run later or on a different computer. If you need to run analyses on a different
computer, you must bring the results file (.dtp) back to the current folder, and then you can use
the File – Read Results menu option to import the results into FRANC3D.
Figure 2.33: Local/Global model connection
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2.6
Step 6: Compute Stress Intensity Factors
Step 6.1: Select Compute SIFs
From the FRANC3D menu, select Cracks and Compute SIFs, Fig 2.34. The Stress Intensity
Factor wizard is displayed, Fig 2.35. You should use the M-integral, but you can check that the
Displacement Correlation results are similar. There are no thermal or crack face
traction/pressure terms. Select Finish and the SIFs Plot window is displayed, Fig 2.36. You can
view the three stress intensity factor (SIF) modes and export the data.
Figure 2.34: Compute SIF’s selected from the Cracks menu
30
Figure 2.35: Compute SIF options
Figure 2.36: Stress Intensity Factor plot
2.7
Step 7: Manual Crack Growth
We manually propagate the crack at this stage. You should at least examine the predicted crack
growth to determine suitable parameters for fitting and extrapolation before proceeding with the
automated crack growth in Section 2.8.
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Step 7.1: Select Grow Crack
From the FRANC3D menu, select Cracks and Grow Crack. The Crack Growth wizard is
displayed, Fig 2.37. In the first panel, we switch to Quasi-Static crack growth. We use quasistatic with a Power Law relationship (between points along the crack front) here as it is the
simplest extension model. Review the reference and theory documents for a description of the
other crack extension models. We use the Max Tensile Stress theory to determine the kink angle;
in this model, crack growth is essentially planar. Select Next.
Figure 2.37: Crack Growth wizard – first panel.
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Step 7.2: Specify Growth Rate
In the second panel, Fig 2.38, the default value of n is 2.0 for the Power Law growth Parameter.
The value of 2 provides reasonable values for the relative crack extension along the crack front.
The material has an isotropic toughness. We will not consider Mode II and III SIFs. We have
only one load case. Select Next.
Figure 2.38: Crack Growth wizard – second panel.
Step 7.3: Specify Fitting and Extrapolation
The next panel shown in Fig 2.39 allows you to specify the crack front point fitting parameters.
You can double click on the (crack) view to see the crack surface. The default growth values are
okay for this model. The median extension is set to 0.15; this value is set automatically based on
the initial template radius so your value might be different. A Fixed Order Polynomial fit with
33
order set to 3 and extrapolation set to 3% at both ends of the crack front is the default; the fitting
parameters might need to be adjusted as the crack grows. Select Next.
Note that the fitted (blue) curve through the predicted new front points (green) must be
extrapolated so that the ends fall outside of the model, but should not be extrapolated too much.
The new front must be extended far enough to provide space between the current and new fronts
along the entire front for new crack geometry to be defined.
Figure 2.39: Crack growth wizard panel for crack front fitting options
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Step 7.4: Specify Crack Front Template
The final panel shown in Fig 2.40 allows you to specify the crack front mesh template
parameters. The crack front mesh template shown in Fig 2.40 extends beyond the model surface,
which is necessary, corresponding to the polynomial extrapolation. Select Next on this panel
when ready to proceed with the crack insertion and remeshing.
Note that the crack geometry for the extended crack is inserted into the original uncracked
model, so do not overwrite or remove the original model files.
Figure 2.40: Crack growth wizard panel for mesh template options
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The resulting new mesh model can be analyzed as was done for the initial crack (see Step 5
above). Note that you will want to give this model a different name, such as Ansys_Cube_
step_001, so that you don’t overwrite the initial crack files. Automated crack growth analyses
are described next.
2.8
Step 8: Automatic Crack Growth
This section describes the steps for automatic crack growth starting from the initial crack model.
We start with an existing FRANC3D model, using the model created in Section 2.4 and 2.5.
Step 8.1: Open FRANC3D Restart File
Start with the FRANC3D graphical user interface (see Fig 2.2) and select File and Open. Select
the file name specified in Section 2.2, called Ansys_Cube_Subdivide.fdb. Select Accept. The
model will be read into FRANC3D (along with the results files that were created when running
the static analysis). We ignore the fact that we already propagated the initial crack in the
previous step, and proceed with setting up the automatic crack growth analysis.
Step 8.2: Select Crack Growth Analysis
From the FRANC3D menu, select Analysis and Crack Growth Analysis. The first panel of the
wizard should appear as in Fig 2.41; it allows you to choose the method for computing SIFs. We
leave all the default values. Select Next.
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Figure 2.41: Crack Growth Analysis wizard – first panel.
Step 8.3: Specify Growth Parameters
The second panel of the wizard should appear as in Fig 2.42. Set the growth type to Quasi-Static
for simplicity. All other values are left as defaults; select Next.
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Figure 2.42: Crack Growth Analysis wizard – second panel.
Step 8.4: Specify Growth Model Data
The third panel should appear as in Fig 2.43. The value of n defaults to 2.0 for quasi-static crack
growth; select Finish.
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Figure 2.43: Crack Growth Analysis wizard – third panel.
Step 8.5: Specify Fitting and Template Parameters
The fourth panel of the wizard should appear as in Fig 2.44. The default values can be used.
Select Next.
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Figure 2.44: Crack Growth Analysis wizard – fourth panel.
Step 8.6: Specify Extension or Cycle Data
The fifth panel should appear as in Fig 2.45. We are growing the crack for 5 steps using a
default Constant Median Crack Growth Increment of 0.2. Select Next.
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Figure 2.45: Crack Growth Analysis wizard – fifth panel.
Step 8.7: Specify Analysis Code
The sixth panel should appear as in Fig 2.46. We use ANSYS and the Current crack growth step
is set to 1 as we are starting from the initial crack. FRANC3D first extends the initial crack, and
then names the resulting set of files as Ansys_Cube_Subdivide_STEP_001.*. Subsequent file
names have the step number incremented as the automatic analysis proceeds. Select FINISH
(button not shown).
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Figure 2.46: Crack Growth Analysis wizard – sixth panel.
Step 8.8: Specify Analysis Options
The seventh panel should appear as in Fig 2.47. Some of the options are specific to your site; we
are using ANSYS 15. The Global model settings should be configured in the same way as for
the original analysis. If there is a global model, the window in Fig 2.48 will appear next, so the
two models can be connected. Click Finish when you are ready to start the automatic crack
growth.
Figure 2.47: Crack Growth Analysis wizard – seventh panel.
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Figure 2.48: Local + Global connection options
FRANC3D saves the .fdb, .cdb and other files for the first crack step model with the name
Ansys_Cube_Subdivide_STEP_001, and then ANSYS starts in the background. If the analyses
stop at any stage, they can be restarted from the last crack step. All of the _STEP_# files are
retained. The model for any step can be read into FRANC3D to view the stress intensity factors
or to restart the analysis with a modified crack growth increment (for example).
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2.9
Step 9: SIF History and Fatigue Life
The stress intensity factor history from the automatic crack growth simulation in Step 8 can now
be displayed. If you still have FRANC3D open and the crack growth from Step 8 is done, you
can proceed with Step 9.1. Otherwise, you can restart FRANC3D and read in the .fdb file for the
last step, using the File - Open menu option.
Step 9.1: Select SIFs Along a Path
From the FRANC3D menu, select Cracks and SIFs Along a Path. If the SIFs have not been
computed yet, the Compute SIFs dialog (see Fig 2.41) is displayed. Leave all the defaults as
before and select Finish.
The Stress Intensity Factors (along a path) dialog should appear, Fig 2.49. The crack fronts are
displayed on the left along with a path through the fronts; the SIF history along the path is shown
in the graph on the right. You can use the tabs above the graph to plot the Mode II and III SIF
history as well as the elastic J-integral and T-stress values along the path. You can define a new
path, Fig 2.50, and you can export the data; for example, you might need to export the Mode I
SIF history (K vs a) to compute fatigue cycles using a different program.
Figure 2.49: SIFs Along a Path dialog – KI plot
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Figure 2.50: SIFs Along a Path dialog – Define Path
Step 9.2: Select SIFs For All Fronts
From the FRANC3D menu, select Cracks and SIFs For All Fronts. If the SIFs have not been
computed yet, the Compute SIFs dialog (see Fig 2.41) will be displayed. Leave all the defaults
as before and select Finish.
The Stress Intensity Factors (for all fronts) dialog should appear, Fig 2.51. The crack fronts are
displayed on the left and the SIFs for all crack fronts are displayed on the right. You can use the
tabs above the plot to display Mode II and III SIFs as well as the elastic J-integral and T-stress
values. If there are multiple crack fronts or multiple load steps, these can be selected using the
drop-down lists; this will be seen in subsequent tutorials.
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Figure 2.51: SIFs for all Fronts dialog – KI plot
Step 9.3: Select Fatigue Life Predictions
From the FRANC3D menu, select Fatigue – Fatigue Life Predictions. If the SIFs have not
been computed yet, the Compute SIFs dialog (see Fig 2.41) will be displayed. Leave all the
defaults as before and select Finish.
The Fatigue Life dialog should appear as in Fig 2.52. The crack fronts are displayed on the left
and the window on the right side should be blank (assuming that lifing parameters have not been
defined previously). You must Set (or Read) Parameters. Selecting Set Parameters displays
the dialog shown in Fig 2.53.
We use Fatigue, Constant Amplitude with Given Stress Ratio (R). We switch the FEM model
units to MPa√mm and then select New Model for the Crack Growth Rate Model.
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Figure 2.52: Fatigue Life dialog
Figure 2.53: Fatigue Life parameters
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The new crack growth rate model dialogs are shown in Fig 2.54. In the first dialog, we switch
the units to MPa-mm. The units can be different from the FE model units, but in this case, we
make them consistent. In the second dialog, we choose Paris as the growth rate model; it is the
default. In the third dialog, we leave the default as Temperature Independent. Finally, in the last
dialog, we set the Paris model parameters; we use made up values here to match our made up
values for cube dimension, material properties and loading.
Note that the Paris exponent ‘n’ is set to 3 whereas we used n=2 for the quasi-static growth. In
practice, you can use the fatigue model and material data to compute growth so that it is
consistent with the fatigue life computations done here. However, it is not strictly necessary, and
it might work better using a lower exponent to predict increments of growth.
Figure 2.54: New Growth Rate model dialogs
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After entering the crack growth rate model parameters, we choose the value for R (which is the
minimum/maximum stress) and choose which load cases to use for computing Kmax (or Kmin),
Fig 2.55. In this case, we use R=0 and there is only one load case. Select Finish.
Figure 2.55: Constant amplitude with given R fatigue life parameter dialogs
The cycles are computed and can be plotted versus crack step number, Fig 2.56, or versus crack
path length. If we choose to plot cycles based on a path, we must select the Define button to
create a path, Fig 2.57. The default path is through the crack front midpoints. Once a path is
defined, the cycles versus crack path length is displayed, Fig 2.58.
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Figure 2.56: Fatigue cycles versus crack step number
Figure 2.57: Define crack path dialog
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Figure 2.58: Fatigue cycles versus crack length
3.0 Tutorial 2: Multiple Load Cases plus Crack Face
Tractions
In the first part of Tutorial 2, we describe the process of importing a model with multiple load
cases. Once a crack is inserted, an additional load case is applied as a crack face pressure. We
describe how to apply a simple constant pressure in the crack in Section 3.5, we describe how to
apply a surface treatment residual stress in Section 3.10, and we describe how to apply meshbased surface crack tractions in Section 3.11.
We use the same Ansys_Cube.cdb file from Tutorial 1, but with two additional load cases. The
first of the extra load cases is a positive (far-field) surface pressure equal in magnitude to the
traction in the first load case; this will compress the cube. The second extra load case is a
negative (far-field) surface traction with double the magnitude of the first load case. Note that
the first extra load case will cause the cube to compress, and we describe how to apply crack face
contact conditions to prevent negative Mode I SIFs in Section 3.8.
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For ANSYS, the load cases can be defined in the .cdb file, separated by “lswrite” commands.
More typically, the load cases are in extra .s## files. In our example file, the first load case is in
the .cdb file and the two extra load cases are in Ansys_Cube.s02 and Ansys_Cube.s03. Note that
the first load case could be contained in Ansys_Cube.s01, but we need to make sure it is not also
contained in the .cdb file.
3.1
Step 1: Reading ANSYS FE Model into FRANC3D
Step 1.1: Importing ANSYS FE Model
Start with the FRANC3D graphical user interface, Fig 3.1, and select File and Import. In the
window shown in Fig 3.2, choose Complete Model. Switch the Mesh File Type radio button in
the Select Import Mesh File window, Fig 3.3, to ANSYS and check the box on the top right side
for Extra load files. Select the file name for the model, called Ansys_Cube.cdb here, Fig, 2.4.
Select Next. The Extra Load Files dialog will be displayed, Fig 3.4. Select both .s02 and .s03
files; use the Shift or Ctrl key to select multiple files.
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Figure 3.1: FRANC3D graphical user interface
Figure 3.2: Import type
Note that we could subdivide the cube as we did in Section 2.3, but for simplicity we just import
the full model here. For relatively simple models, the time to remesh the volume is short.
However, for most models, we want to subdivide to avoid having to remesh the full model at
each step of crack growth.
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Figure 3.3: Select Input Mesh File dialog box with Extra load files checked
Figure 3.4: Select Extra Load Files dialog
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Step 1.2: Select the Retained Items in the FE Model
The next panel, Fig. 3.5, allows you to choose the mesh surface facets that are retained from the
ANSYS files. Surfaces with boundary conditions appear in blue as shown in Fig 3.6, and turn
red when selected, Fig 3.7. We retain the surfaces with boundary conditions (top and bottom of
the cube) by choosing Select All. The boundary conditions are transferred automatically to the
new mesh when the crack is inserted. Select Finish. Note that the boundary conditions for all
load cases are applied to the same surfaces in this model.
Figure 3.5: Select Retained BC Surfaces wizard panel.
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Figure 3.6: ANSYS Model retain BC Surfaces wizard panel.
Figure 3.7: ANSYS Model retain BC Surfaces wizard panel.
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Step 1.3: Displaying the FE Model
The model is displayed in the main window. You can turn on the surface mesh and manipulate
the view. The model should appear as in Fig 3.8, which shows that the mesh is retained on the
top and bottom (not shown) surfaces where the boundary conditions are applied.
Figure 3.8: ANSYS model imported into FRANC3D, showing retained facets on the top.
3.2
Step 2: Insert Crack From File
From the FRANC3D menu, select Cracks and Flaw From Files, Fig 3.9. The first panel of the
wizard appears as in Fig 3.10. Choose the Cube_Crack.crk file and hit Accept. The flaw being
added is a circle with radius=1, centered on the front face and parallel to the xz-plane. This crack
was created using the New Flaw Wizard with the save to file option in Section 2.4.
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Figure 3.9: Flaw From Files option in Crack menu.
The next panel of the wizard, Fig 3.11, allows you to adjust the location of the flaw. The
orientation cannot be changed. The final panel, Fig 3.12, allows you to set the template mesh.
We just leave all the defaults in these panels and select Next and Finish.
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Figure 3.10: Flaw from file dialog to select .crk file.
Figure 3.11: Flaw wizard panel to set location.
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Figure 3.12: Flaw geometry shown in the model with crack template mesh
3.3
Step 3: Apply Crack Surface Traction
From the FRANC3D main menu, select Loads and Crack Face Pressure/Traction, Fig 3.13.
Click on Add in the dialog box shown in the top left panel of Fig 3.14. Choose Constant Crack
Face Pressure, as shown in the top right panel of Fig 3.14; it is the default, and select Next. Set
the Pressure value to 1 in the next dialog, Fig 3.14 – bottom left, and select Finish. Note that a
positive pressure value will tend to open the crack. The original dialog now contains one entry,
Fig 3.14 – bottom right; click Accept.
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Figure 3.13: Crack Face Pressure/Traction menu
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Figure 3.14 Crack face traction dialogs.
3.4
Step 4: Static Analysis
Step 4.1: Run ANSYS static crack analysis
From the FRANC3D menu, select Analysis and Static Crack Analysis. The first panel of the
wizard should appear as in Fig 3.15. We specify the file name for the FRANC3D database; we
call it Ansys_Cube_LoadCases.fdb here. Select Next once you enter a File Name. The next
panel of the wizard, Fig 3.16, allows you to specify the solver; choose ANSYS and then click
Next.
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Figure 3.15: Static Analysis wizard first panel – File Name.
Figure 3.16: Static Analysis wizard second panel – solver.
The next panel of the wizard, Fig 3.17, allows you to specify the ANSYS analysis and output
options. The Apply crack face tractions box is checked automatically. There is no global model;
click Finish when ready to proceed with the ANSYS analysis. When ANSYS is done, proceed
to Step 4.2.
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Figure 3.17: Static Analysis wizard third panel – ANSYS output options.
Step 4.2: Compute SIFs
We now compute the stress intensity factors for this crack. If you are able to run ANSYS from
FRANC3D, then the results (.dtp) file is read automatically. From the FRANC3D menu, select
Cracks and Compute SIFs. When the Compute SIFs dialog is displayed, Fig 3.18, make sure
that the Include Applied Crack Traction box is checked; select Finish and the SIFs Plot dialog is
displayed, Fig 3.19. The initial plot shows the sum of KI for all load cases. You can view the
three stress intensity factor (SIF) modes for the four load cases. Fig 3.20 shows the KI values for
the four load cases.
Note that load case 2 has a negative KI. This is the compression load case and we did not
include crack face contact in the analysis, so the crack faces penetrate each other giving a
negative crack opening. In the next step, we turn on crack face contact and redo the analysis.
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Figure 3.18: Compute SIFs dialog.
Figure 3.19: Stress Intensity Factor dialog – sum of Mode I SIFs.
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Figure 3.20: Stress Intensity Factor dialog – Mode I SIFs for each of the 4 load cases.
Step 4.3: Re-Run ANSYS static crack analysis with crack face contact
From the FRANC3D menu, select Analysis and Static Crack Analysis. The first panel of the
wizard should appear as seen previously in Fig 3.15. We specify the file name for the
FRANC3D database; we call it Ansys_Cube_LC_CFC.fdb here. Select Next once you enter a
File Name. The next panel of the wizard, as seen in Fig 3.16, allows us to specify the solver;
choose ANSYS and then click Next.
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The next panel of the wizard, Fig 3.21, allows you to specify the ANSYS analysis and output
options. The Apply crack face tractions box is checked automatically. We need to check the
Define crack face contact box, which enables the Contact button. Click this button and the
dialog shown in Fig 3.22 is displayed. In practice, you must make sure that these parameters do
not conflict with any ANSYS data already in the model. We can leave all the defaults here
except we set the coefficient of friction to be 0.5. Click Accept and then click Finish in the
previous panel, Fig 3.21, when ready to proceed with the ANSYS analysis.
Figure 3.21: Static Analysis wizard third panel – ANSYS output options.
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Figure 3.22: ANSYS contact options.
Step 4.4: Compute SIFs with crack face contact
We now compute the stress intensity factors for this crack. If you are able to run ANSYS from
FRANC3D, then the results (.dtp) file will be read automatically. From the FRANC3D menu,
select Cracks and Compute SIFs. When the Compute SIFs dialog is displayed, Fig 3.23, make
sure that the Include Applied Crack Traction and the Include Contact Crack Pressure boxes are
checked; select Finish and the SIFs Plot dialog is displayed, Fig 3.24. The initial plot shows the
sum of KI for all load cases. Fig 3.25 shows the KI values for the second load case. Note that
value is closer to 0.0 than previous, although it is still not equal to 0.0. Contact analyses are
subject to some numerical error; to verify that the SIF results from the M-integral are correct, we
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compare to the SIF results using Displacement Correlation. In the Compute SIFs dialog, choose
Displacement Correlation, Fig 3.26. The Mode I SIFs for load case 2 are shown in Fig 3.27.
The results are comparable to those for M-integral.
Figure 3.23: Compute SIFs dialog.
Figure 3.24: Stress Intensity Factor dialog – sum of Mode I SIFs.
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Figure 3.25: Stress Intensity Factor dialog – Mode I SIFs for the second load case using the Mintegral.
Figure 3.26: Compute SIFs dialog.
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Figure 3.27: Stress Intensity Factor dialog – Mode I SIFs for the second load case using
Displacement Correlation
3.5
Step 5: Apply Surface Treatment Residual Stress
To simulate residual stress due to a surface treatment, such as shot-peening, FRANC3D allows
you to define a 1-D stress profile as a function of distance from the surface. We will demonstrate
this using the original Ansys_Cube.cdb model with one far-field load step (see Tutorial #1).
Start with the FRANC3D graphical user interface (see Fig 3.1), and select File and Import. In
the window shown in Fig 3.2, choose Complete Model. Switch the Mesh File Type radio button
in the Select Import Mesh File window, (see Fig 3.3), to ANSYS. Note that we are not using the
extra load steps in this demonstration. Select the file name for the model, called Ansys_Cube.cdb
here, and then select Next. As before, we choose to retain all the boundary condition surfaces
(see Figs 3.5 – 3.7). The model will appear as was shown in Fig 3.8.
Insert the same crack from file as before (see Figs 3.9 – 3.12). At this stage, we could do a static
analysis to verify that the model is correct and compute the SIFs for the far-field loading only;
the Mode I SIF should be the same as that shown in the top left panel of Fig 3.20. We leave this
as an exercise for the reader. The next step is to define the surface treatment residual stress.
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From the FRANC3D main menu, select Loads and Crack Face Pressure/Traction, Fig 3.28.
Click on Add in the dialog box shown in the left panel of Fig 3.29. Choose Surface Treatment
Residual Stress, as show in the right panel of Fig 3.29, and select Next. The dialog shown in Fig
3.30 is displayed. We use Read From File to import the residual stress distribution from a .txt
file. Using the Open File dialog shown in Fig 3.31, we select the file surf_treat_res.txt, and then
hit Accept. The distribution is read and displayed in the dialog, Fig 3.32. Select Next on this
dialog panel to choose the surface of the model that is treated. The dialog shown in Fig 3.33
appears with all surfaces shown as blue; use the Shift key and the left mouse button to select the
front surface of the model. Once selected, the surface is colored red/pink. Select Finish and the
original Add Traction dialog is displayed with one entry, Fig 3.34; click Accept.
Figure 3.28: Loads – Crack Face Pressure/Traction menu item selected.
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Figure 3.29: Crack Face Traction wizard panels; surface treatment selected.
Figure 3.30: Surface treatment residual stress panel.
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Figure 3.31: Select file for surface treatment residual stress.
Figure 3.32: Surface treatment residual stress panel - residual stress distribution displayed.
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Figure 3.33: Surface treatment residual stress panel to select the treated surface.
Figure 3.34: Crack Face Traction wizard panel - surface treatment added.
From the FRANC3D menu, select Analysis and Static Crack Analysis. We specify the file
name for the FRANC3D database; we call it Ansys_Cube_surf_treat.fdb here; select Next once
you enter a File Name. The next panel of the wizard allows you to specify the solver; choose
ANSYS and the click Next. The next panel of the wizard allows you to specify the ANSYS
analysis and output options. The Apply crack face tractions box is checked automatically. Click
Finish when ready to proceed with the ANSYS analysis.
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Once ANSYS is finished, from the FRANC3D menu, select Cracks and Compute SIFs. When
the Compute SIFs dialog is displayed make sure that the Include Applied Crack Traction box is
checked; select Finish and the SIFs Plot dialog is displayed, Fig 3.35. The initial plot shows the
sum of KI for both load cases. The lower two panels of Fig 3.35 show the KI values for the first
and second load cases separately. The first load case is the same as previously computed. The
second load case produces a negative SIF indicating that this residual stress tends to keep the
crack from opening, which is generally the purpose of surface treatment.
Figure 3.35: Mode I SIF plots showing the sum (top) and the individual load case values;
surface treatment load case produces a negative SIF (bottom right).
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3.6
Step 6: Apply Tractions from Mesh-Based Stress
Step 6.1: Create Mesh-Based Stress Field
This section describes how to apply a crack surface traction using pre-computed stresses from an
uncracked model. The uncracked model will typically be the same as the model that we use for
crack growth simulations. In this example, we use the Ansys_Cube model along with ANSYS
stresses; although, we could use ABAQUS or NASTRAN model and stresses.
To create the mesh-based stresses, we start with the base cube model and define an arbitrary farfield stress on the top surface of the cube, Fig 3.36. This creates a stress field that varies in the xdirection, Fig 3.37. FRANC3D reads the ANSYS stress listing, Fig 3.38. In ANSYS, we turn
off PowerGraphics, change the format for the listing (using the /Format command), create the
nodal stress component listing (using the ‘prnsol,s’ command), and save the listing to a file; we
call it Ansys_Cube_surf_gradient.str. The stress listing must be in the global Cartesian
coordinate system. We also must save the corresponding Ansys_Cube_surf_gradient.cdb file.
Note that if you use ABAQUS to generate the stresses for this tutorial, you need to write out the
.fil file or write an ABAQUS CAE report (.rpt) file that contains the nodal stresses. FRANC3D
will import an .inp and either the .fil or .rpt file. Additionally, if you are using ABAQUS CAE,
to create the model, you should set NoPartsInputFile=ON to create a “flat” .inp file prior to
running the analysis so that the stress listing has node ids that correspond exactly to the .inp file.
See Step 6.3 of the FRANC3D/ABAQUS Tutorial for more details.
If you use NASTRAN to create the stress, FRANC3D reads .bdf (or .nas) files along with .pch
files with the nodal stress data.
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Figure 3.36: Arbitrary far-field surface pressure.
Figure 3.37: Stress in the y-direction for the arbitrary far-field surface pressure.
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Figure 3.38: Nodal stress component listing.
Step 6.2: Apply Mesh-Based Stress as Crack Face Traction
Start with the FRANC3D graphical user interface (see Fig 3.1), and select File and Import. In
the window shown in Fig 3.2, choose Complete Model. Switch the Mesh File Type radio button
in the Select Import Mesh File window, (see Fig 3.3), to ANSYS. Note that we will not use
extra load steps in this demonstration; use the model from Tutorial #1. Select the file name for
the model, called Ansys_Cube.cdb, and then select Next. As before, we choose to retain all the
boundary condition surfaces (see Figs 3.5 – 3.7). The resulting model was shown in Fig 3.8.
Insert the same crack from file as before (see Figs 3.9 – 3.12). At this stage, we could do a static
analysis to verify that the model is correct and compute the SIFs for the far-field loading only;
the Mode I SIF should be the same as that shown in the top left panel of Fig 3.20. We leave this
as an exercise for the reader. The next step is to define the mesh-based crack surface traction.
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From the FRANC3D main menu, select Loads and Crack Face Pressure/Traction, Fig 3.39.
Click on Add in the dialog box shown in the left panel of Fig 3.40. Choose Residual Stress
Defined on a Mesh, as show in the right panel of Fig 3.40, and select Next. The dialog shown on
the left side of Fig 3.41 is displayed. We select the files for the mesh and the stress listing, and
then hit Next; the original Add Traction dialog is displayed with one entry, Fig 3.41 – right side;
click Accept.
Figure 3.39: Loads – Crack Face Pressure/Traction menu item selected.
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Figure 3.40: Crack Face Traction wizard panels; residual stress defined on a mesh selected.
Figure 3.41: Crack Face Traction wizard panels for residual stress defined on a mesh.
From the FRANC3D menu, select Analysis and Static Crack Analysis. We specify the file
name for the FRANC3D database; we call it Ansys_Cube_mesh_based.fdb here; select Next
once you enter a File Name. The next panel of the wizard allows you to specify the solver;
choose ANSYS and the click Next. The next panel of the wizard allows you to specify the
ANSYS analysis and output options. The Apply crack face tractions box is checked
automatically. Click Finish when ready to proceed with the ANSYS analysis.
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Once ANSYS is finished, from the FRANC3D menu, select Cracks and Compute SIFs. When
the Compute SIFs dialog is displayed make sure that the Include Applied Crack Traction box is
checked; select Finish and the SIFs Plot dialog is displayed, Fig 3.42. The initial plot shows the
sum of KI for both load cases. The lower two panels of Fig 3.42 show the KI values for the first
and second load cases separately. The first load case is the same as previously computed. The
second load case produces a negative SIF with a gradient due to the mesh-based crack face
tractions.
Figure 3.42: Mode I SIF plots showing the sum (top) and the individual load case values; meshbased stress load case produces a negative SIF (bottom right).
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4.0 Tutorial 3: Two Cubes Glued Together
In Tutorial 3, we use two cubes that are glued together to illustrate how to simulate crack growth
in models where there is contact or constraint between parts of the model.
4.1
Step 1: Create the ANSYS FE Model
We use the same initial cube geometry and boundary conditions from the first tutorial and add a
second adjacent cube, Fig 4.1, with slightly different material properties. The second cube has
an elastic modulus of 20,000, which is double that of the first cube; the Poisson ratio is the same.
The second cube is also constrained in the y-direction and has a surface traction (negative
pressure) of 10 on the upper surface, which is the same as the first cube.
We define contact conditions between the two cubes. The bottom image of Fig 4.1 shows the
contact elements. The first set of analyses use always-bonded contact conditions, Fig 4.2. The
ANSYS cdb file is exported as doublecube_ansys.cdb here.
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Figure 4.1: ANSYS double cube model with contact surface between the cubes.
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Figure 4.2: ANSYS contact wizard, with always-bonded contact selected.
4.2
Step 2: Import ANSYS FE Model into FRANC3D
We start by importing the ANSYS model into FRANC3D, using the .cdb file written in the
previous step, and we import as a full model.
Step 2.1: Importing ANSYS FE Model
Start with the FRANC3D graphical user interface, and select File and Import. In the Select Type
of Import panel, choose Complete Model and select Next. Switch the Mesh File Type radio
button in the Select Import Mesh File window to ANSYS and select the file name for the model,
called doublecube_ansys.cdb, Fig 4.3. Select Next.
Figure 4.3: FRANC3D FE model import.
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The Select Retained Surfaces dialog is displayed, Fig 4.4. The surfaces with boundary
conditions and the contact surface are highlighted in blue. Choose Select All to retain all of
these surfaces.
Figure 4.4: FRANC3D select retained surfaces.
Step 2.2: Insert a Crack
We insert a surface penny crack with radius of 1.0 in the second cube, Fig 4.5. Note that this
crack is the same as that defined in Tutorial #1, except that it is translated in the x-direction so it
falls in the second cube. The template mesh radius is left at the default value of 0.1, which is
what was used for Tutorial #1. The resulting remeshed model is shown in Fig 4.6; the contact
surface mesh facets between the two cubes are retained.
Note that the contact surface mesh does not have to be retained, and if the crack is located such
that the contact surface must be remeshed, we must not retain it. Here we retain it for simplicity
and for demonstration. We show what happens if we do not retain it in Step 2.6.
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Figure 4.5: FRANC3D new crack insertion panel showing location and orientation.
Figure 4.6: Remeshed cracked model, with contact surface mesh facets retained.
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Step 2.3: Static Crack Analysis
We run a static analysis using ANSYS. From the FRANC3D Analysis menu, select Static
Crack Analysis. Set the file name, we use Ansys_glued_cubes_crack.fdb here. Select the
ANSYS solver; all the default settings are used. Note that the .cdb file written by FRANC3D
includes ANSYS commands to regenerate the always-bonded contact between the two cubes.
Step 2.4: Compute SIFs
The resulting Mode I SIF is shown in Fig 4.7; the curve is not symmetric as it was for Tutorial 1.
Figure 4.7: Mode I SIFs for double_cube with always-bonded contact.
Step 2.5: Plot Deformed Shape
We can plot the deformed shape in FRANC3D. From the Advanced menu select View
Response. Fig 4.8 shows that the displacement is not uniform; the first cube deforms about
twice as much as the second, which is expected as it has a lower elastic modulus. The alwaysbonded contact between the two cubes is maintained.
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Figure 4.8: Deformed shape – 200x magnification.
Step 2.6: Contact surface mesh not retained
If we choose to not retain the mesh on the contact surface when importing the FE model into
FRANC3D (refer back to Step 2.1), we have to specifically unselect the contact surfaces, Fig
4.9; note that we unselect both sides of the interface here. Unselect/select is done using the Shift
key with the left mouse button. Note that you will have to use the Clipping button to see inside
the model.
Insert the same crack as in Step 2.2, into the second cube. The resulting surface mesh shown in
Fig 4.10 has a remeshed contact surface. The static analysis is done using ANSYS as in Step
2.3. The resulting Mode I SIFs, Fig 4.11, are the same as computed previously (see Fig 4.7).
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Figure 4.9: Import FE double_cube model with contact surface unselected.
Figure 4.10: Double_cube model with unretained contact surface remeshed.
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Figure 4.11: Mode I SIFs for double_cube with unretained contact surface mesh.
Step 2.7: Specify No Crack Material Region
If the crack in the second cube is allowed to propagate, it will reach the interface between the
two cubes. Depending on the material interface, the crack might stop or it might cross the
interface. If the crack should stop at the interface but continue growing in the original ‘cube’
material region, we can specify that the other ‘cube’ material region is not to be cracked.
Using the FRANC3D Advanced menu, select No Crack Regions, Fig 4.12. The dialog shown
in Fig 4.13 is displayed.
Figure 4.12: Advanced menu – No Crack Regions option.
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Figure 4.13: No Crack Regions dialog - uncracked model (left) and cracked model (right).
5.0 Tutorial 4: Disk with Rotation and Temperature
In Tutorial 4, we simulate crack growth in a simple disk model that includes temperature
variation and rotation. In Step 1, we describe briefly the model and the thermal analysis to
produce the temperature variation. Once the temperatures are defined, we run a structural
analysis that also includes rotation. With this model we can then proceed to do the crack growth
simulation. A goal of this tutorial is to show how temperature variation affects computed SIFs.
5.1
Step 1: Create the ANSYS Disk Model
The first step is to build the ANSYS FE model and to define the material properties. The outline
of the disk model is shown in the left panel of Fig 5.1. The inner radius is set to 1.0 and the outer
radius is set to 10. The disk is set to be one unit wide; the final geometry is shown in the right
panel of Fig 5.1.
We define both the thermal and structural properties, which will consist of density, specific heat,
enthalpy, thermal expansion, conductivity, elastic modulus and Poisson ratio. The material can
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be temperature dependent; for this analysis we use constant values for all data except for the
elastic modulus, Fig 5.2. Density is set to 1.0 and enthalpy is set to 0.
Figure 5.1: ANSYS disk geometry.
Figure 5.2: ANSYS disk material properties.
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5.2
Step 2: Run ANSYS Thermal Analysis
The first analysis is for heat transfer, so we set the element type (Solid87) and create a volume
mesh. The model is meshed with all tetrahedral elements, left panel of Fig 5.3. The boundary
conditions consist of temperatures on two surfaces; temperature at the inner radius of the disk is
set to 1000 and temperature at the outer radius is set to 100, right panel of Fig 5.3. The resulting
nodal temperatures are shown in Fig 5.4. These nodal temperatures are applied to the model as
initial conditions for the mechanical analysis.
Figure 5.3: Volume mesh and thermal boundary conditions.
Figure 5.4: Resulting nodal temperature contours.
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5.3
Step 3: Run ANSYS Structural Analysis
We switch the element type in the model (Solid87 to Solid92) for the structural analysis. The
boundary conditions for the structural analysis consist of rollers on the (symmetry) surfaces at
x=0 and y=0. We also fix a point in the z-direction to prevent rigid body motion, and we apply
the temperatures from the heat analysis as initial conditions. Finally, we define the rotational
velocity (omega) as 0.53 about the z-axis. The resulting model with boundary conditions should
appear as in the left panel of Fig 5.5. The resulting maximum principal stress contours from the
structural analysis are show in the right panel of Fig 5.5.
We save the ANSYS db file in case we need to re-analyze the model. We also archive the model
to a .cdb file for use with FRANC3D. Note that we could create global and local model portions
in ANSYS for FRANC3D. However, for this tutorial we rely on the FRANC3D submodeler
tool, so we will just archive the full model; use “cdwite,DB,file_name,cdb”.
Figure 5.5: Boundary conditions for structural analysis – left panel,
and resulting maximum principal stress contours – right panel.
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5.4
Step 4: Import Disk into FRANC3D
Start with the FRANC3D graphical user interface, and select File and Import. In the Select Type
of Import panel, choose the Import and divide into global and local models radio button and
select Next. Switch the Mesh File Type radio button in the Select Import Mesh File window to
ANSYS and select the file name for the model, called Ansys_Disk.cdb, Fig 5.6. Select Next.
Figure 5.6: FRANC3D FE model import.
Figure 5.7: FRANC3D FE model import.
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Figure 5.8: FRANC3D FE model import.
5.5
Step 5: Insert Initial Crack
We insert an elliptical crack with a radius of 0.1, Fig 5.9. The crack is located at the front of the
disk, rotated 45 degrees from the x-axis, Fig 5.10. The crack front template has a radius of 0.01,
Fig 5.11. The resulting remeshed crack model is shown in Fig 5.12.
Figure 5.9: Elliptical crack dimension dialog.
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Figure 5.10: Crack location and orientation dialog.
Figure 5.11: Crack front template dialog.
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Figure 5.12: Final meshed crack model.
5.6
Step 6: Static Crack Analysis
We perform a static crack analysis using ANSYS. Choose Analysis and Static Crack Analysis
from the FRANC3D menu. Provide a file name (Ansys_disk_crack.fdb) and choose ANSYS as
the solver. The ANSYS options are shown in Fig 5.13; the default settings will cause ANSYS to
write nodal temperatures to the results (.dtp) file. The Connect to global model option is checked
automatically. Select Next.
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Figure 5.13: Static analysis options for ANSYS.
The next dialog box has options for connecting the local and global portions. We use node
merging with the automatically selected local and global cut-surfaces. Click Finish to begin the
ANSYS analysis.
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Figure 5.14: Static analysis ANSYS local/global model connection dialog.
5.6
Step 6: Compute SIFs
Once ANSYS has finished running, we compute the SIFs; choose Cracks and Compute SIFs
from the FRANC3D menu. The dialog, Fig 5.15, allows you to specify the method for
computing SIFs. If we use the M-integral, we make sure that the Include Thermal Terms option
is checked; the Reference Temperature is 0 degrees for this model. The SIFs based on the Mintegral are shown in Fig 5.16 and the SIFs based on Displacement Correlation (DC) are shown
in Fig 5.17. It should be noted that the SIFs differ very little, indicating that the results are
computed correctly. If your results differ significantly, you should ensure that the nodal
temperatures are all correct. Note that if you do not include the thermals terms when computing
M-integral SIFs, the results will be very different from the DC SIFs, Fig 5.18.
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Figure 5.15: Compute SIFs dialog.
Figure 5.16: M-Integral based SIFs.
102
Figure 5.17: Displacement correlation based SIFs.
Figure 5.18: M-Integral based SIFs without thermal terms added.
5.7
Step 7: Crack Growth
The next step is to propagate the crack. Choose Cracks and Grow Crack from the FRANC3D
menu. We switch to quasi-static growth, Fig 5.19, and select Next. We leave all the defaults in
the next panel, Fig 5.20, and select Next. The median extension is set to 0.015, and the
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extrapolation is increased to 4% for both ends, Fig 5.21. The template radius is set to 0.01, Fig
5.22. Select Next when ready to start the process of crack growth, insertion and remeshing.
Note that the crack front and template should extend beyond the model surface at every step; this
sometimes requires small adjustments in the fitting depending on the crack front and model
surface geometry. For this model, 3% extrapolation is not quite enough to ensure that all the
template end points fall outside of the model.
Figure 5.19: Crack growth first wizard panel.
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Figure 5.20: Crack growth second wizard panel.
Figure 5.21: Crack growth third wizard panel.
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Figure 5.22: Crack growth wizard – final panel.
5.8
Step 8: Automatic Crack Growth
We can continue doing static analyses and manually growing the crack at each step or we can do
automatic crack growth. We proceed with automatic crack growth at this point. Select Crack
Growth Analysis from the Analysis menu. A series of dialog panels some of which you have
just seen in Step 7 when manually growing the crack will be displayed; use the same settings.
We specify 10 crack growth steps with a constant median increment, Fig 5.23. We set the
current crack growth step to 1 as we have extended the crack but have not yet analyzed it, Fig
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5.24. The last two panels are the same as those for Step 6 (see Fig 5.13 and 5.14). All the
default settings should be okay; select Finish to start the automatic growth.
Figure 5.23: Crack growth plan dialog for automatic crack growth.
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Figure 5.24: Crack growth step number and base file name dialog for automatic crack growth.
5.9
Step 9: Analysis Results
After 10 steps of crack growth using a constant increment of 0.015, the crack appears as in Fig
5.25. You can monitor the FRANC3D CMD window for any error messages as well as
monitoring the ANSYS logs. The SIF history is shown in Fig 5.26. You can continue to grow
this crack and/or you can compute fatigue cycles – we leave this as an exercise.
We can examine the temperature contours in ANSYS to verify that these are mapped correctly,
Fig 5.27. The deformed shape of the crack at step #11 is shown in Fig 5.28.
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Figure 5.25: Crack configuration after 10 steps of automatic crack growth.
Figure 5.26: Mode I SIF history after 10 steps of automatic crack growth.
109
Figure 5.27: Contours of structural temperatures at crack step #11.
Figure 5.28: Deformed shape of crack step #11.
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6.0 Tutorial 5: Multiple Cracks in a Plate
In Tutorial 5, we simulate multiple cracks using a simple plate model.
6.1
Step 1: Create the ANSYS Plate Model
The plate dimensions are defined as: 20 x 50 x 5. The bottom surface is fixed in the y-direction
and the top surface has a traction of 10. Additional constraints on the bottom left edge prevent
motion in the x-direction, and the node at the origin is also fixed in the z-direction, Fig 6.1.
Figure 6.1: ANSYS plate model.
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The material properties are shown in Fig 6.2. The model is meshed with 20-noded brick
elements. Once the model has been defined and analyzed in ANSYS to verify that the boundary
conditions are suitable, the model can be archived to a .cdb file; we call it Ansys_plate.cdb.
Figure 6.2: ANSYS plate model material properties.
6.2
Step 2: Import Plate Model into FRANC3D
From the FRANC3D menu, we select File and Import. We Import and divide the plate model,
Fig 6.3. We extract the mid-portion of the plate using the Rubberband tool in the Submodeler
window, Fig 6.4. Select Crop and Next in this dialog to extract the portion of the model
selected. There are no boundary conditions on this middle portion, so the model is immediately
displayed in the FRANC3D main window, Fig 6.5. The cut-surface mesh facets are
automatically retained.
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Figure 6.3: FRANC3D model import of plate model.
Figure 6.4: FRANC3D submodel extraction for plate model.
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Figure 6.5: Plate submodel in FRANC3D main window – Multiple Flaw Insert menu selected.
6.3
Step 3: Insert Multiple Cracks
From the FRANC3D menu, select Cracks and Multiple Flaw Insert, Fig 6.5. The dialog
shown in Fig 6.6 is displayed. Use the Add button to define each crack that will be added.
Note that one could also define single cracks using the New Flaw Wizard menu, save each
crack to a file without adding it to the model, and then use the Flaws From Files to add the
multiple .crk files.
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Figure 6.6: Multiple crack definition dialog.
After selecting Add, the usual Flaw Definition wizard panels are displayed. Figs 6.7 – 6.10
provide the parameters for the first crack, which is a middle (or center) through crack. This
crack has two fronts. The crack geometry must be defined such that intersections between the
crack and model can be computed; we set g=5.2 as the plate is 5.0.
Figure 6.7: Flaw definition – middle through crack selected.
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Figure 6.8: Middle through crack dimensions.
Figure 6.9: Middle through crack orientation.
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Figure 6.10: Middle through crack template.
Select the Meshing Parameters button in Fig 6.10 to display the dialog in Fig 6.11. Turn off
the Do Coarsen Crack Mouth Mesh so that we generate a more refined mesh to help improve the
results. A coarse tetrahedral mesh near the crack typically leads to a rough SIF curve.
Figure 6.11: Meshing parameters – Do Coarsen Crack Mouth Mesh turned off.
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Once the template is defined, select Finish, Fig 6.10, and the Multiple Crack Definition dialog
shows the first crack name, Fig 6.12. Select Add again to add the second crack, which will be an
edge through crack, with one crack front, Fig 6.13.
Figure 6.12: Multiple crack definition dialog with one crack defined.
Figure 6.13: Flaw definition – edge through crack selected.
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The crack geometry is again defined such that it is bigger than the plate and such that it is bigger
(0.6) than what we intend the crack depth to be (0.5), Fig 6.14. You must orient the crack so that
the front falls inside the model, Fig 6.15; if you are unsure of the orientation, select Next and
look at the template, Fig 6.16. If you set the orientation incorrectly, select Back to fix it. When
you are done, select Finish. The Multiple Crack Definition dialog shows two crack names, Fig
6.17.
Figure 6.14: Edge through crack dimensions.
Figure 6.15: Edge through crack orientation.
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Figure 6.16: Edge through crack template.
Figure 6.17: Multiple crack definition dialog with two cracks defined.
Select Add again to add the third crack, which will be a long shallow crack, Fig 6.18. Note that
we typically use this crack instead of high-aspect ratio ellipses as the geometry at the ends is
better for the template mesh. The crack geometry is again defined such that intersection with the
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plate surface can easily be computed, Fig 6.19 - 6.20. Select Finish, Fig 6.21, to return to the
Multiple Crack Definition dialog, which now shows three crack names, Fig 6.22.
Figure 6.18: Flaw definition – long shallow crack selected.
Figure 6.19: Long shallow crack dimensions.
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Figure 6.20: Long shallow crack orientation.
Figure 6.21: Long shallow crack template.
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Figure 6.22: Multiple crack definition dialog with three cracks defined.
Select the Display button, Fig 6.22, to show all three cracks in the model, Fig 6.23. The cracks
should not be overlapping or intersecting.
Figure 6.23: Multiple cracks displayed together.
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Select Accept, Fig 6.22, to start the crack insertion and remeshing process. Note that you can
use the Add / save radio button to save the cracks to a .crk file first if you think you might need
to restart from this initial configuration; you might want to vary the mesh refinement (template
radius) for instance. The remeshed model is shown in Fig 6.24. We can now proceed with the
static analysis.
6.4
Step 4: Static Crack Analysis
Follow the same procedure as in the previous tutorials to run the ANSYS analysis. Select Static
Crack Analysis from the FRANC3D menu, set the file name (we use Ansys_plate_multi_crack),
set the ANSYS options, Fig 6.25, set the local + global connection, Fig 6.26, and select Finish.
Figure 6.24: Remeshed model with three cracks inserted.
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Figure 6.25: Static analysis wizard panel to set ANSYS solver options.
Figure 6.26: Static analysis wizard panel to set local / global connection.
125
6.5
Step 5: Compute SIFs for Multiple Crack Fronts
Once ANSYS has finished, select Compute SIFs from the FRANC3D menu. The SIF dialog
allows you to select specific crack fronts to display SIF plots. The front is identified on the left
by the red A and B. As you grow the crack, you will have SIF curves from all fronts for all crack
growth steps. And if there are multiple load steps, you will have separate SIF curves for each of
those also.
Figure 6.27: Mode I SIF for crack front #3.
6.6
Step 6: Grow Multiple Cracks
Select Grow Cracks from the FRANC3D menu. We switch to quasi-static growth as in Tutorial
4 and leave all the other parameters at their default values. We end up with the dialog shown in
Fig 6.28, which shows predicted crack growth for all four crack fronts. We set the median
extension to 0.15 to ensure that we have growth for all fronts. Note that you can turn off growth
for a specific crack front by unchecking the grow box. Each front has its own fitting parameters.
In this case, this is important as the front on the left side can easily be fit to a 3rd order
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polynomial (2nd order would work too), Fig 6.29. The front on the right must use a different type
of fit, Fig 6.30. For this crack front, a cubic spline or moving polynomial fit would work;
however, we use the multiple polynomial here. Once you have checked the fit, you can proceed
to re-insert and remesh to grow all three cracks.
Note that FRANC3D currently does not track crack front ids perfectly; so as the cracks grow,
crack front ids might vary or change.
Figure 6.28: Crack growth wizard panel.
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Figure 6.29: Crack growth wizard panel – showing crack front #2.
128
Figure 6.30: Crack growth wizard panel – showing crack front #3.
6.7
Step 7: Grow Crack around a Corner
In this section, we describe how to grow a crack around a 90 degree corner, creating a throughedge-crack from a corner-crack shape. Import the local portion of the plate model that was
created during Step 2. We can import as “already divided” or we can subdivide again choosing
the retained element listing. The model will appear as in Fig 6.5.
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We insert a single crack, using the elliptical shape from the flaw library. The crack radius is 1.0.
It is located as shown in Figure 6.31. The mesh template settings are left at their default values.
Figure 6.31: Single corner crack location and orientation.
An initial static crack analysis is completed to obtain the initial SIFs, Fig 6.32. The crack growth
is done using the quasi-static growth model with n=2. The initial growth and fitting parameters
are shown in Fig 6.33. To keep things simple, 24 steps of automated crack growth are completed
using this same constant median extension. The mesh template parameters are left at their
default values.
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Figure 6.32: Single corner crack SIFs.
Figure 6.33: Single corner crack initial growth.
131
At step #24, the crack front is close to the back surface. The crack will transition from a corner
crack to an edge crack, and this can happen automatically (Fig 6.34), but if a user wants to
capture SIF values as the crack transitions, then some “manual” crack growth steps and static
analyses can be performed.
Fig 6.35 shows a series of manual crack growth steps where the median increment is adjusted so
that the crack front transitions in a user-controlled manner around the corner. Note that when the
crack front is at the corner, and when it intersects the model surface at shallow angles, we can
turn on Simple Intersections for the template mesh. This forces the template to be pulled back
from the model surface; FRANC3D should turn this on automatically as needed, but we can
ensure that it is on by checking the box (see middle right image). If the back surface of the plate
is not being refined enough when the crack front is close, you can edit the Meshing Parameters
and turn on Do Local Surface Refinement (see bottom right image).
Figure 6.34: Single corner crack after 24 steps (left) and after 26 steps (right) of growth.
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Figure 6.35: Manual steps of growth for single corner crack as it transitions around a corner.
6.8
Step 8: Grow Crack through a Back Surface
In this section, we describe how to grow a crack through a back-surface, creating a centerthrough-crack with two fronts from a surface-penny crack in a plate. The steps to grow a crack
front through a back-surface are similar to those for transitioning a crack around a corner. We
use manual crack growth and static analysis steps when the crack front gets close to the surface
and as it breaks through. We describe the steps here using the same plate model but with a single
surface-penny crack inserted on the front surface of the plate.
Import the local portion of the plate model that was created during Step 2. We can import as
“already divided” or we can subdivide again choosing the retained element listing. The model
will appear as in Fig 6.5.
We insert a single crack, using the elliptical shape from the flaw library. The crack radius is 1.0.
It is located as shown in Figure 6.36. The mesh template settings are left at their default values.
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Figure 6.36: Single surface crack location and orientation.
An initial static crack analysis is completed to obtain the initial SIFs, Fig 6.37. The crack growth
is done using the quasi-static growth model with n=2. The initial growth increment and fitting
parameters are shown in Fig 6.38. To keep things simple, automated crack growth is completed
using a constant median extension for 10 steps, and then a slightly larger extension for another
10 steps, etc. The mesh template parameters are left at their default values.
Figure 6.37: Single surface crack SIFs.
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Figure 6.38: Surface crack growth parameters.
At step #28, the crack front is close to the back surface. The crack will transition from a surface
crack to a center-through crack, and this might happen automatically, but if a user wants to
capture SIF values as the crack transitions, then some “manual” crack growth steps and static
analyses can be performed.
Fig 6.39 shows a series of manual crack growth steps where the median increment is adjusted so
that the crack front transitions in a user-controlled way toward and through the back-surface. If
the back surface of the plate is not being refined enough when the crack front is close, you can
edit the Meshing Parameters and turn on Do Local Surface Refinement (top left image). The
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crack increment and template radius can be reduced to get the front close to the back surface
before breaking through, but there needs to be enough room to volume-mesh (top right image).
Eventually, the crack must be propagated through the back surface (bottom left image). Note
that when the crack front intersects the model surface at shallow angles, we can turn on Simple
Intersections for the template mesh. This forces the template to be pulled back from the model
surface; FRANC3D should turn this on automatically as needed, but we can ensure that it is on
by checking the box (bottom right image). When the crack front intersects the back surface at a
more reasonable angle (closer to a right angle), the Simple Intersection can be turned off.
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Figure 6.39: Surface crack in a plate after automatic growth to the back surface of the plate; usercontrolled growth and static analysis allows controlled break-through of the back surface.
7.0 Tutorial 6: Computing Fatigue Life Cycles
In Tutorial 6, we describe the Fatigue module in more detail by presenting an example
simulation of a surface crack in a plate under cyclic loading, comparing the computed number of
cycles to experimental values from: Manu, C. (1980) Three-dimensional finite element analysis
of cyclic fatigue crack growth of multiple surface flaws, PhD Thesis, Cornell University.
The plate and initial crack dimensions are shown in Fig 7.1. The loading is uniaxial tension.
The physical testing produced the crack growth seen in Fig 7.2. The crack grows through the
plate, eventually becoming a center-through crack with two crack fronts.
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Figure 7.1: Single surface crack in plate under tension:
Figure 7.2: Single surface crack in plate under tension (from Manu, 1980).
The crack growth is simulated using FRANC3D and ANSYS. Fig 7.3 shows the simulated crack
fronts. The fatigue cycles are computed using the resulting SIF history and appropriate crack
growth rate material data. For units of MPa and mm, the Paris parameters for this material are:
C=1.14e-15 and m=3.85; Kth is 121 MPa•mm½ and KIc is 6949 MPa•mm ½. The cycles are
compared to previous simulations and experimental observations from: Barlow, K., 2008,
Propagation Simulation of Multiple Cracks in a Tensile Specimen, International Conference on
Fatigue Damage of Structural Materials VII, Hyannis, MA.
139
Figure 7.3: FRANC3D simulated crack growth for single surface crack in a plate in tension
Figure 7.4: Crack growth cycles for single surface crack in plate under tension.
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7.1
Step 1: Perform Crack Growth
The first step is to import the ANSYS model of the plate into FRANC3D. We import and divide
the full model using the FRANC3D Submodel tool, Fig 7.5. There are no boundary conditions
on the local model; it is displayed in the FRANC3D main modeling window with the cut-surface
facets retained once we Crop and finish with the Submodel tool.
Figure 7.5: Local and global model portions.
The semi-elliptical surface crack dimensions are defined in Fig 7.1. We use a template radius of
0.25, set the number of template rings to 6, and turn off the Do Crack Mouth Coarsen Mesh flag
to generate a more refined mesh to compare the SIFs to the handbook solution, Fig 7.6.
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460
455
450
445
440
435
Newman-Raju
430
FRANC3D
425
0.0
0.2
0.4
0.6
0.8
1.0
Figure 7.7: Mode I SIF for initial semi-elliptical surface crack – comparing FRANC3D with
handbook solution.
The crack growth could be simulated using a few steps with relatively large increments, but we
use a larger number of steps with small increments of growth. For the initial analyses, the
growth is based on constant amplitude loading with Paris crack growth rate material data, as
given in Fig 7.1. Variable amplitude loading options are discussed in Step 3.
Using the automatic Crack Growth Analysis menu option in FRANC3D, the crack is
propagated for 55 steps with crack fronts as shown in Fig 7.3. The Mode I SIF history is shown
in Fig 7.8 for a path through the first 48 crack fronts. This SIF history can be exported and used
in an external program to compute fatigue life or crack growth cycles; in Step 2, we describe
how the Fatigue module built into FRANC3D is used to compute cycles.
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Figure 7.8: Mode I SIF history.
7.2
Step 2: Compute Fatigue Crack Growth Cycles
The crack growth in Step 1 was performed using a constant amplitude loading with Paris fatigue
parameters. When we select Fatigue and Fatigue Life Predictions from the FRANC3D main
menu, the dialog shown in Fig 7.9 is displayed. The cycles versus crack growth step number are
plotted by default. The number of cycles is computed at each step of growth and stored in the
FRANC3D database; the number of cycles is an average of the values computed at each mid-side
node along the crack front.
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Figure 7.9: Mode I SIF history – cycles vs crack step number.
The Fatigue Life dialog also allows us to plot cycles versus crack length, Fig 7.10 and 7.11,
where the length might be the crack length measured on the model surface, which is what was
observed and measured during the experiments. Regardless of the path chosen, the number of
cycles is consistent, if the path goes through all of the fronts.
The number of cycles is 112,026 at the current configuration, where the crack front is very close
to the back surface of the plate, but has not yet broken through; there is about 0.75 mm between
the deepest point on the crack front and the back surface. This number of cycles is based on
constant amplitude loading with R=0, which is not representative of the actual tests.
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Figure 7.10: Mode I SIF history – define a path on the model surface.
Figure 7.11: Mode I SIF history – cycles vs crack length.
7.3
Step 3: Crack Growth and Fatigue Options
The applied (measured) loading spectrum from the Manu experiments is shown in Fig 7.4. It
consists of a complete history of ‘blocks’ of constant amplitude load cycles, where the ‘blocks’
have different R values (where R = minimum load / maximum load) and different numbers of
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cycles. There are only two different R values (0.15 and 0.575), and these values differentiate the
‘blocks’ of cycles. There are a total of 375,370 cycles applied during the test, which consists of
47 constant amplitude blocks.
The options for crack growth in FRANC3D consist of: 1) quasi-static which implies a single
constant or a simply increasing load, 2) constant amplitude cyclic load, 3) variable amplitude
sequence loads, 4) variable amplitude spectrum loads, and 5) variable amplitude transient loads.
The constant amplitude cyclic loading was used in Step 1 and 2 above, with R=0. The computed
number of cycles is significantly less than the number measured in the experiment, which is
expected as the K value is higher, and thus the crack growth rate is much higher. If we modify
the R value in the Fatigue Life dialog and use 0.15, Fig 7.12, the computed cycles increases to
209,421. We can also try setting R to 0.575, and in that case the number of cycles is 3,020,415.
Figure 7.12: Fatigue Life dialog – Life Parameters with R set to 0.15.
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7.3.1 Variable Amplitude Loading
The three variable amplitude load options are briefly described here.
The sequence option involves a number of load steps (or load cases). For example, for a jet
engine component, a user defines a set of load steps where each step has a different temperature
distribution and a different angular velocity; each load step represents a different time point in a
typical flight (e.g., ground idle, takeoff/climb, cruse, maneuver, decent, reverse thrust). The load
step order in the analysis does not need to correspond to how they would be encountered in a real
flight. In FRANC3D, a user constructs a ‘Load Sequence’ (or mission profile) that describes a
typical mission or flight. For each stage in the sequence, an optional load and temperature
multiplier can be applied, giving a sequence table such as:
Load_Step
1
3
2
4
2
4
2
5
1
Load_Mult
1.0
1.0
1.0
0.8
1.1
1.2
1.0
1.0
1.0
Temp_Mult
0.5
1.0
1.0
1.0
1.0
1.1
1.0
1.0
1.0
Comment
Ground idle (cold)
Climb
Initial cruse
Maneuver 1
Second cruse
Maneuver 2
Third cruse
Descent
Ground idle (hot)
FRANC3D computes SIFs for each of the stages in the sequence and then steps through those
SIFs and find the K and R for each reversal (e.g. from ‘off’ to ‘ground idle’). For each K and
R, FRANC3D finds da = da/dN(K,R,T), and sums the da's for each stage in the sequence to get
da total for one pass through the sequence. Note that da is the change in crack length. Each pass
through the sequence represents one flight. FRANC3D passes through the sequence as many
times as necessary to predict crack length as a function of number of flights (rather than as a
function of the number of cycles).
Spectrum loading involves a load history that defines the stress level at a (typically large)
147
number of time points. This load history is “counted” using "rainflow" or other method to come
up with a list of load reversals (stress_max and stress_min pairs). This is a counted load
spectrum, and there are industry standard spectra (e.g. FALSTAFF, TWIST, TURBISTAN and
HELIX).
FRANC3D steps through the spectrum one load reversal at a time. For the current crack length,
FRANC3D computes the sum of the K's from one or more analysis load steps (as per the user's
input) and multiplies the nominal K by the stress_max and stress_min values to get K_max and
K_min for the current load reversal. FRANC3D then computes K and R, and then da =
da/dN(K,R,T). The crack length is updated and the computation repeated.
Transient loading involves a series of load steps that mimic a ‘moving’ load or a load that
changes in time. An example of this is gear tooth contact; as two gears rotate the load on a tooth
changes in magnitude and location as the tooth comes into and goes out of contact with the
opposing tooth. Another example is the changing load on a railway wheel as it comes into and
goes out of contact with the track as the wheel revolves. In these cases, the user defines a set of
load steps in (time) sequence. FRANC3D computes the SIFs for each load step and computes an
increment of crack growth, both extension and direction. The resulting vector sum of all the
increments for all load steps gives the total crack growth for one instance of the transient series.
7.3.2 Spectrum Loading for Manu Model
The Manu load spectrum can be read into FRANC3D and used to compute cycles, Fig 7.13. The
number of cycles computed by FRANC3D is 323,070, which is relatively close to the number of
cycles in the test. Fig 7.14 shows the series of FRANC3D dialog boxes used to read and define
the Manu load spectrum. The same Paris crack growth model and data that was used during
crack growth is used here.
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Figure 7.13: Fatigue Life dialog – using Manu average spectrum.
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Figure 7.14: Variable amplitude load spectrum dialogs – using Manu average spectrum.
7.4
Step 3: Sequence Crack Growth
As described in 7.3, the sequence crack growth option in FRANC3D uses the results from a set
of load steps. In this step of the tutorial, we use the simple disk model from Section 4 with three
unique load cases. The load steps will consist of: 1) rotation with initial constant temperature,
2) rotation with increased temperature distribution, and 3) load step #2 with additional surface
pressure. To be completed….
7.5
Step 4: Spectrum Crack Growth
As described in 7.3, the spectrum crack growth option in FRANC3D uses the results from one or
more load steps in combination with a load spectrum (file). In this step of the tutorial, we use the
simple disk model from Section 4 with a single load case and two different made-up spectrum
files. To be completed….
7.6
Step 5: Transient Crack Growth
As described in 7.3, the transient crack growth option in FRANC3D uses the results from
multiple load steps, and crack growth is based on the combined (vector sum) results. In this step
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of the tutorial, we use a portion of a gear model with load steps that mimic discrete time points as
the gear teeth rotate. To be completed….
8.0 Tutorial 7: Resume Growth with Larger Submodel
In Tutorial 7, we describe the process of extracting the current crack geometry and inserting this
into a larger submodel to resume crack growth for the case when the crack reaches the limits of
the submodel.
8.1
Step 1: Extract and Save Crack Geometry
The crack geometry information for each step of crack growth is saved in the FRANC3D restart
(.fdb) file. The data appears in this block:
FLAWSURF
(
VERSION: 5
NUM_SURFS: 763
SURF: 0
263 264 356
6.83559456365193
…
…
4.73891556707121
)
5.00380971299962
9.72712346638146
5.00420103803897
8.3468309877949
This data can be copied from the .fdb file and saved to a .crk file, using any text editor.
Using the example from Tutorial 1, we open the Ansys_Cube_sub_STEP_006.fdb file, copy the
FLAWSURF data, and save it to a .crk file, called Ansys_Cube_step_6.crk here.
At step 6, the crack is approaching the boundary of the submodel region, Fig 8.1, so we could not
have grown the crack much further in Tutorial 1.
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Figure 8.1: Ansys_cube model at crack step #6 from Tutorial 1.
8.2
Step 2: Restart from Saved Crack Geometry
Start FRANC3D, and from the menu select File and Import. We could extract a larger
submodel region from the cube, but for this example, we will just import the full cube model and
run subsequent crack growth simulations using the full model. Select Import a complete model
from the dialog, Fig 8.2, and then set the Mesh File Type to ANSYS and select the
Ansys_Cube.cdb file, Fig 8.3; select Accept to continue.
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Figure 8.2: FRANC3D model import dialog.
Figure 8.3: FRANC3D mesh import file selector.
We use the Select All button in the next dialog, Fig 8.4, to retain all the mesh facets where
boundary conditions are applied. Select FINISH when ready; the model will be imported and
then displayed in the FRANC3D main window.
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Figure 8.4: Use Select All button to retain all highlighted mesh facets.
From the FRANC3D menu, select Cracks and Flaw From Files. Select the
Ansys_Cube_step_6.crk file, Fig 8.5, which was extracted and saved previously from the .fdb
data, and select Accept. The .crk file is read and then displayed in the Orient User Flaw dialog,
Fig 8.6. Note that the crack geometry includes the original circular crack and all the subsequent
steps of growth. Also note that part of the geometry falls outside the model so that intersections
can be computed correctly. In general, a crack that is read from a file can be translated in
Cartesian space, but for continuing crack growth, we do not want to do this.
Figure 8.5: Select step_6.crk file.
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Figure 8.6: Step 6 crack geometry displayed in cube model.
Select Next to set the mesh template parameters, Fig 8.7; we just use the defaults. Select Finish
when ready; the crack will be inserted and the model remeshed.
Figure 8.7: Step 6 crack mesh template.
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From the FRANC3D menu, select Static Crack Analysis and set all the analysis parameters the
same as for Tutorial 1 (see Section 2.5). The only thing that is changed here is the file name so
that we do not overwrite the original submodel step files; we call it Ansys_cube_STEP_006, Fig
8.8.
This analysis produces SIFs that are identical (or nearly so) to the SIFs computed for the last step
when using the smaller submodel region. Fig 8.9 shows the Mode I SIFs for the two cases.
There is a small difference as the mesh around the crack front is different. At this point, the
crack can be propagated further; we do another 6 steps of crack growth here.
After propagating the crack an additional 6 steps, we can combine the SIF history for the two
analyses. We do this using the FRANC3D Advanced menu option: Create Growth History.
Figure 8.8: Set FRANC3D restart file name – don’t overwrite previous step 6 files.
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Figure 8.9: Step 6 Mode I SIFs for the original submodel analysis (top) compared with the new
results using the full model (bottom).
8.3
Step 3: Combine SIF Histories
Start FRANC3D, and select the File and Open menu option. Select the
Ansys_Cube_sub_STEP_006.fdb file, Fig 8.10, and select Accept. From the Advanced menu,
select Create Growth History, Fig 8.11. The Compute SIFs dialog is displayed; select Finish.
The dialog shown in Fig 8.12 is displayed. Note that the initial crack is labeled as CrackStep_1
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and then there are 6 steps of growth after that. You can use the Plot menu command to display
the crack fronts, Fig 8.13.
Figure 8.10: FRANC3D restart file selector.
Figure 8.11: FRANC3D Advanced menu.
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Figure 8.12: Create Growth History dialog – submodel data.
Figure 8.13: Create Growth History dialog.
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Using the File menu in the Create Growth History dialog, select Save History, Fig 8.14, and
save the SIF history to a .fcg file, called Ansys_Cube_sub_steps.fcg here. Close this dialog using
the Cancel button, and then close the model in FRANC3D using the main File menu Close
option. Now open the Ansys_Cube_STEP_012.fdb file using the File menu Open option. As
with the submodel, we save the SIF history for the full model. The SIF history for the full model
is shown in Fig 8.15. Note that CrackStep_1 gives the same SIFs as CrackStep_7 in the
submodel, Fig 8.12. However, note that CrackStep_1 includes Extension data.
Figure 8.14: Create Growth History dialog File menu.
Figure 8.15: Create Growth History dialog – full model data.
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Save the full model SIF history to a .fcg file, called Ansys_Cube_full_steps.fcg here. Close the
Create Growth History dialog and close the model. This leaves the FRANC3D main model
window empty, and the Advanced menu has only one active entry, Fig 8.16. Select the Create
Growth History menu option to display the dialog. It does not have any CrackGrowthData.
Figure 8.16: Advanced menu when there is no model data.
Use the File menu and select Read History, Fig 8.17. Select the Ansys_Cube_sub_steps.fcg file.
Then using the same menu, select Append History and select the Ansys_Cube_full_steps.fcg
file. Note that there will be 14 steps of crack data at this stage. We need to delete CrackStep_7
from the Submodel data as it does not include Extension data. We highlight CrackStep_7, Fig
8.18, and then right-click the mouse to display the submenu, Fig 8.19. Select Delete Crack Step
and it will be removed, leaving 13 crack steps. You can plot the combined fronts, Fig 8.20.
Figure 8.17: Create Growth History dialog – File menu.
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Figure 8.18: Create Growth History dialog – combined SIF history data.
Figure 8.19: Right-mouse button click on the CrackStep_7 to delete.
Use the File menu in this dialog to save the combined SIF history to a .fcg file, called
Ansys_Cube_combined_steps.fcg here. The dialog can be closed by selecting the Cancel button
at the bottom; selecting the Save button prompts you save the history data to file.
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Figure 8.20: Create Growth History dialog – combined crack fronts.
The combined SIF history data can be imported into the Fatigue Life module using the Read SIF
Data button, Fig 8.21. Once you have Set Parameters, you can plot cycles and SIF data. See
Section 7 for more details on the Fatigue Life dialog.
Figure 8.21: Fatigue Life dialog.
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9.0 Tutorial 8: Fretting Fatigue
In Tutorial 8, we describe the Fretting Fatigue module by presenting an example simulation,
using an ANSYS finite element model of a fretting test rig.
Figure 9.1: Fretting test rig (from: Golden, IJF, 31, 2009).
9.1
Step 1: Saving ANSYS Data
The ANSYS model is shown in Fig 9.2. Using symmetry, only one quarter of the actual model
is required. There are two load steps applied; the deformed shapes for both cases are shown in
Fig 9.3. The specimen (darker blue colored piece in Figure 9.2) is pulled downward and then
partially unloaded; the load ratio (R) is 0.1. There is contact between the specimen and the
fretting pad; the coefficient of friction is 0.3.
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Figure 9.2 ANSYS model of fretting test rig.
Figure 9.3 Fretting test rig deformed shape for load step #1 (left) and #2 (right).
Using the ANSYS post-processor, nodal results are extracted and saved to ASCII files. The
results must be in the global Cartesian coordinate system. The following ANSYS ADPL
commands are used:
/graphics,off
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rsys,0
/format,,g,20,12
prnsol,s
prnsol,epto
prnsol,dof
prnsol,cont
Each set of results for each load step are saved to files with the following extensions: .str, .stn,
.dsp and .con. The base file name should be the same for each extension, we use fretting_rig_ls1
and fretting_rig_ls2. In addition to these results, we must also save the ANSYS model to a .cdb
file, called fretting_rig.cdb here.
9.2
Step 2: Fretting Model Import
Start FRANC3D and from the main menu, choose Fretting and Read model and results, Fig
9.4. You are prompted to select the model file; in this case, we choose the fretting_rig.cdb file,
Fig 9.5; the default file type is ANSYS, but ABAQUS or NASTRAN model files can also be
read. You are then prompted to select the results files, Fig 9.6. In this case, we have two load
steps corresponding to Qmax and Qmin conditions, where Q represents the load that causes
sliding (and ultimately the fretting). Select the .str file corresponding to each load case (the .stn,
.dsp and .con files will be read automatically). Select Finish to proceed to the next step, which
will define the contact surface(s) where fretting is to be evaluated.
Figure 9.4 FRANC3D menu selection for fretting analysis.
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Figure 9.5 FRANC3D mesh model file selector for fretting module.
Figure 9.6 FRANC3D results file selector for fretting module.
The next dialog, Fig 9.7, allows you to select the materials and contact surfaces. In this case, we
can select all materials and have the contact surface selected automatically as there is only one.
For models with multiple contact surfaces, you might want to choose the master and slave
surfaces of interest, Fig 9.8. You can also choose the edge of contact node set if it is defined;
otherwise, the nodes on the boundary of the contact region will be determined from the analysis
results. Select Finish and the model will be displayed in the FRANC3D main window; the
material regions will be colored if the materials are different, Fig 9.9
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Figure 9.7 Fretting model data filter – auto selected contact surfaces.
Figure 9.8 Fretting model data filter to select master and slave contact surfaces.
Note that we did not have to choose the .stn, .dsp and .con files separately. As long as the base
file names are the same as for the .str file, they will be read automatically.
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Figure 9.9 Fretting test rig model displayed in FRANC3D.
9.3
Step 3: Fretting Crack Nucleation
The next step is to compute the fretting nucleation parameters. From the FRANC3D Fretting
menu, select Fretting crack nucleation, Fig 9.10. There are five fretting nucleation models
available. The models have been described in the literature; they use some or all of the results
data that was read earlier to compute a fretting nucleation parameter. The computed fretting
parameter is then compared with empirical or test data to determine number of fretting cycles to
discrete crack nucleation.
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Figure 9.10 Fretting crack nucleation menu option.
Figure 9.11 Fretting nucleation models.
For this example, we choose the Equivalent Stress nucleation model, and select Next (not
shown). The next dialog, Fig 9.12, allows you to specify the model parameters used to compute
the Seq value along with the number of cycles. FRANC3D computes the Seq values at nodes in
the contact region and then computes number of cycles (Ni) based on the equation shown at the
top of the dialog.
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Figure 9.12 Equivalent stress fretting nucleation model parameters.
Select Next to proceed to the final dialog, Fig 9.13, which allows you to display the contact
surfaces, and color contours of fretting nucleation cycles or nucleation parameter, Fig 9.14.
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Figure 9.13 Fretting nucleation display window.
The Equivalent Stress model requires several material dependent parameters. For this example,
the material is Ti-6Al-4V, which corresponds with the default parameters in the dialog; these
parameters were obtained from the literature.
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Figure 9.14 Seq contours on fretting specimen surface.
9.3
Step 3: Discrete Crack Nucleation
Assuming that fretting fatigue causes crack nucleation, we will extract a submodel and insert a
crack and run the analysis in this section. The first step is to import the model; we choose to
import and subdivide and select the fretting_rig.cdb file, Fig 9.15. Note that we need to check
the Extra load files box so that we can import the two load step files as well, Fig 9.16.
Figure 9.15: Import the fretting rig model.
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Figure 9.16: Import the load step files also.
The submodeler tool is displayed once the files are imported, Fig 9.17. The first selection can be
done using the By Material option; click the Select button and check material #4, Fig 9.17- left
panel. Use the Crop button to remove the remainder of the model, Fig 9.17 – right panel.
Figure 9.17: Submodel selection based on material id 4.
Next we use the Rubberband Box tool to select a smaller submodel, Fig 9.18. Note that this
submodel includes the entire contact surface region; this is important to remember when we are
going to set up the static analysis of the full model as we will have to redefine the contact by
adding an extra connection.
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Figure 9.18: Submodel selection based on a Rubberband box.
After extracting the appropriate submodel and saving the local and global ANSYS .cdb files, the
dialog in Fig 9.19 is displayed. This allows us to retain the mesh facets where the boundary
conditions are applied. In this case, we do not select these facets as the surface must be
remeshed to accommodate the through crack that we are inserting. Just select Finish in this
dialog, and the model will be displayed in the FRANC3D main model window.
A shallow through (or edge) crack is inserted near the lower edge of contact at the location
predicted by the fretting nucleation model(s). Fig 9.20 shows two views of such a crack. Note
that for shallow cracks, it is a good idea to change the default meshing parameters when setting
the crack front template. Fig 9.21 shows the meshing parameters dialog with Do Local Surface
Refinement checked and Do Coarsen Crack Mouth Mesh unchecked. The resulting remeshed
cracked submodel is shown in Fig 9.22.
175
Figure 9.19: Select retained surfaces dialog – do not select this surface.
Figure 9.20: Through crack near the lower edge of contact.
176
Figure 9.21: Meshing parameters dialog.
Figure 9.22: Cracked remeshed submodel.
177
This portion of the model is combined with the global model and the analysis of this combined
model is done using ANSYS. The user controls the analysis step using the Static Analysis
dialogs in FRANC3D, shown in Figs 9.23 – 9.26. An extra connection for the contact between
the fretting pad and specimen is defined using paired contact, Fig 9.24.
Figure 9.23: Static analysis dialogs.
Figure 9.24: Static analysis dialogs.
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Figure 9.25: Static analysis dialogs.
Figure 9.26: Static analysis dialogs.
179
The resulting contact surfaces are shown in Figure 9.27. The analysis produces results as shown
in Figure 9.28, which shows the deformed mesh in dark-blue with the white dashed lines
representing the original shape. The Mode I SIFs along the crack front are shown in Fig 9.29,
for the first load step.
Figure 9.27: New contact surfaces.
Figure 9.28: Deformed shape after analysis.
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Figure 9.29: Mode SIFs for first load step.
10.0 Tutorial 9: Multiple Submodel Portions
In Tutorial 9, we describe how to extract multiple portions of a full model to create a submodel,
which might be useful when inserting multiple cracks into a model where the cracks are far
apart. We will use the plate model from Section 6, Figure 10.1, to demonstrate.
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Figure 10.1: ANSYS plate model.
10.1 Step 1: Import Plate Model into FRANC3D
From the FRANC3D menu, we select File and Import. We Import and divide the plate model,
Fig 10.2. We first extract the mid-portion of the plate using the Rubberband tool in the
Submodeler, Figure 10.3. Select Crop and then continue with the subsequent Rubberband
selections and Crops as shown in Figures 10.4-6. Note that we switch the cropping option to
highlight the inverse selection in Figures 10.4-6.
Figure 10.2: FRANC3D model import of plate model.
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Figure 10.3: FRANC3D first submodel extraction for plate model.
Figure 10.4: FRANC3D second submodel extraction for plate model.
183
Figure 10.5: FRANC3D third submodel extraction for plate model.
Figure 10.6: FRANC3D fourth submodel extraction for plate model.
Select Next in Figure 10.6 after selecting Crop, and the model will be displayed in the
FRANC3D main model window, Figure 10.7. There are no boundary conditions on these two
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portions. The cut-surface mesh facets for both portions are retained automatically. The next step
is to insert cracks into the two portions; we insert edge through cracks in the next step.
10.2 Step 2: Insert Multiple Cracks
From the FRANC3D menu, we select Cracks and Multiple Flaw Insert. The dialog shown in
Fig 10.8 is displayed. Use the Add button to define the two edge cracks. Figure 10.9 shows the
dimensions for both edge cracks that will be inserted. Figures 10.10-11 show the location,
orientation and mesh template for crack #1, and Figures 10.12-13 show the location, orientation
and mesh template for crack #2.
Figure 10.7: FRANC3D main window with two portions of the full model.
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Figure 10.8: Multiple crack definition dialog.
Figure 10.9: FRANC3D edge through crack definition.
186
Figure 10.10: FRANC3D edge through crack location and orientation – crack #1.
Figure 10.11: FRANC3D edge through crack mesh template – crack #1.
187
Figure 10.12: FRANC3D edge through crack location and orientation – crack #2.
Figure 10.13: FRANC3D edge through crack mesh template – crack #2.
After defining both edge cracks, the Multiple Crack dialog shows the two crack names, Figure
10.14. Click on Display in this dialog to show the cracks in the model, Figure 10.15. Click
188
Accept (in Figure 10.14) to finish crack insertion and remeshing. The resulting model is shown
in Figure 10.16.
Figure 10.14: FRANC3D multiple crack insertion dialog.
Figure 10.15: FRANC3D multiple crack insertion display.
189
Figure 10.16: FRANC3D main window with edge cracks in two separate model portions.
10.3 Step 3: Crack Analysis
Follow the same procedure as in the previous tutorials to run the ANSYS static crack analysis.
Select Static Crack Analysis from the FRANC3D menu, set the file name, make sure the local
+ global connection is set, and run ANSYS.
Once ANSYS has finished, select Compute SIFs from the FRANC3D menu. The SIF dialog
allows you to select specific crack fronts to display SIF plots. The front is identified on the left
by the red A and B. Figure 10.17 shows the SIF for crack #1, and Figure 10.18 shows the SIF
for crack #2.
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Figure 10.17: Mode I SIF for crack #1.
Figure 10.18: Mode I SIF for crack #2.
The cracks can be propagated as described in previous tutorials; see Section 6.6 for example.
Figure 10.19 shows the crack growth dialog. Subsequent crack growth is left as an exercise for
the reader.
191
Figure 10.19: Crack growth dialog.
11.0 Tutorial 10: Session Log Playback
In Tutorial 10, we describe the session log and its playback. When running the FRANC3D
(GUI) program, a session log file is saved for (almost) every menu command that is executed.
The session log file is a text file that can be edited, played back in the FRANC3D GUI, played
back from the command line, and/or converted to a Python script that can be used with the
FRANC3D Python module. The session log file number in the current working directory is
incremented each time FRANC3D is started using that directory.
As an example, the session log file for Tutorial 1 is given here:
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# session log for tutorial 1
Submodeler(
model_type=ANSYS,
orig_file_name='Ansys_Cube.cdb',
submodel_file_name='Ansys_Cube_LOCAL.cdb',
global_file_name='Ansys_Cube_GLOBAL.cdb',
elem_file_name=' Ansys_Cube_RETAINED_ELEMS.txt')
OpenMeshModel(
model_type=ANSYS,
file_name='Ansys_Cube_LOCAL.cdb',
global_name='Ansys_Cube_GLOBAL.cdb')
InsertFileFlaw(
file_name='Cube_Crack.crk')
RunAnalysis(
model_type=ANSYS,
file_name='Ansys_Cube_sub.fdb',
flags=[OUTPUT_MAT,OUTPUT_CS,NO_WRITE_TEMP,TRANSFER_BC,NO_CFACE_TRACT,NO_
CFACE_CNTCT],
merge_tol=0.0001,
connection_type=MERGE,
element_series_type=SOLID_185_187,
executable='ANSYS150.exe',
command='" ANSYS150.exe" -b -p struct
-i "Ansys_Cube_sub.macro" –o "Ansys_Cube_sub.out"',
global_model=' Ansys_Cube_GLOBAL.cdb',
merge_surf_labels=[AUTO_CUT_SURF],
global_surf_labels=[GLOBAL_CONNECT_SURF],
offset_mat=0,
offset_csys=0,
license=struct,
crack_face_contact=false)
ComputeSif()
SetGrowthParams(
load_model=QS_EXPONENTIAL,
kink_angle_strategy=MTS,
const_median_step=0.15)
GrowCrack(
load_model=QS_EXPONENTIAL,
kink_angle_strategy=MTS,
const_median_step=0.15,
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temp_radius_type=ABSOLUTE,
temp_radius=0.1)
SetGrowthParams(
load_model=QS_EXPONENTIAL,
kink_angle_strategy=MTS,
const_median_step=0.15)
AutoGrowthAnsys(
cur_step=1,
file_name='Ansys_Cube_sub',
load_model=QS_EXPONENTIAL,
kink_angle_strategy=MTS,
const_median_step=0.15,
num_steps=5,
step_type=SCONST,
const_step_size=0.15,
temp_radius_type=ABSOLUTE,
temp_radius=0.1,
flags=[OUTPUT_MAT,OUTPUT_CS,NO_WRITE_TEMP,TRANSFER_BC,NO_CFACE_TRACT,NO_
CFACE_CNTCT],
merge_tol=0.0001,
connection_type=MERGE,
element_series_type=SOLID_185_187,
executable='ANSYS150.exe',
command='" ANSYS150.exe" -b -p struct
-i "Ansys_Cube_sub_STEP_001.macro" -o "Ansys_Cube_sub_STEP_001.out" ',
global_model='Ansys_Cube_GLOBAL.cdb',
merge_surf_labels=[AUTO_CUT_SURF],
global_surf_labels=[GLOBAL_CONNECT_SURF],
offset_mat=0,
offset_csys=0,
license=struct,
crack_face_contact=false)
WriteSifPath(
file_name='cube_crack_sif_hist_p5.sif',
load_step=1,
flags=[TAB,A,KI,KII,KIII,CRD])
Start the FRANC3D GUI, and choose File and Playback. Using the file selector, Fig 11.1,
choose the session log file and select Accept. FRANC3D will read the log file and process the
commands; so in this case the ANSYS cube model is subdivided, the crack is inserted and
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analyzed, and then propagated for five steps. Finally the SIF history is extracted and written to a
file.
A playback.log file is written that includes all of the commands and any FRANC3D messages.
If something goes wrong, you should first open the playback log file, which is a text file, and
look at the last command that was attempted. The playback.log should be written to the current
working directory, but if that is not set, it might be saved to the folder where FRANC3D is
located.
Figure 11.1: Select session log file to play back in FRANC3D.
12.0 Tutorial 11: Python Interface
In Tutorial 11, we briefly describe how to use the Python module. The Python module is
designed to work with Python version 2.7.8; it should work with versions between 2.7.6 and
2.7.11.
The FRANC3D session log (see Tutorial 10) can be converted to Python using the Fcl2Py
executable that is shipped with FRANC3D. This program takes one argument, which is the
session (command) file name. It reads the commands from the file, converts them to equivalent
Python script, and writes the information to stdout, which can be piped to a file. For example:
 C:/examples/Fcl2Py.exe session01.log > ses01.py
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The ses01.py file will be similar to:
#!/usr/bin/python
import sys
sys.path.append("/home/bruce/hg/v7/franc3d_v7/Drivers")
import PyF3D
f3d = PyF3D.F3DApp()
# session log for tutorial 1
f3d.Submodeler(
model_type="ANSYS",
orig_file_name='cube.cdb',
submodel_file_name='cube_LOCAL.cdb',
global_file_name='cube_GLOBAL.cdb',
elem_file_name='cube_RETAINED_ELEMS.txt')
f3d.OpenMeshModel(
model_type="ANSYS",
file_name='cube_LOCAL.cdb',
global_name='cube_GLOBAL.cdb')
f3d.InsertFileFlaw(
file_name='cube_02.crk')
f3d.RunAnalysis(
model_type="ANSYS",
file_name='cube_surf_v7.fdb',
flags=["NO_WRITE_TEMP","TRANSFER_BC","NO_CFACE_TRACT","NO_CFACE_CNTCT"],
merge_tol=0.0001,
connection_type="MERGE",
executable='ansys',
command='ansys –i cube_surf_v7.macro –o cube_surf-v7.log',
global_model='cube_GLOBAL.cdb',
merge_surf_labels=["AUTO_CUT_SURF"],
global_surf_labels=["GLOBAL_CONNECT_SURF"])
f3d.ComputeSif()
You can run this script from the command line:
 python ses01.py
This assumes that Python (2.7.8) is in your PATH and that you are running from within the
folder where the ses01.py and corresponding FE files exist.
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13.0 Tutorial 12: ANSYS Workbench
In Tutorial 12, we describe the ANSYS Workbench interface. Workbench combined with
simple ADPL commands can be used to create CDB files which can be used in FRANC3D. The
following shows the process with an example model.
A model is created in Workbench and a Mechanical ADPL is linked to the setup. This is used to
edit the models in ANSYS Classic to create the CDB files if the commands in Workbench Setup
are not used.
Mechanical APDL
linked to Setup, Use
right click and Edit
in Mechanical
APDL
Figure 13.1: Workbench Interface to ANSYS Classic.
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Figure 13.2: Basic Example Model with Temps, Pressures, Forces, Contacts, Cyclic Symmetry
Named Local and
Global Models
LOCAL_MODE
L
Commands to
export Local and
Global CDB files
Figure 13.2: Model Defining the Local and Global Models
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The following method was used to create the local and global cdb models for use in FRANC3D.
Ansys Workbench:
- materials
- geometry (sub-models)
* Global model
* Local model
* Interface
- coordinate systems
- loads, mission
- boundary conditions
-APDL commands
- Change Units (EMUNIT)
- Check Jacobian values
- add SHPP,OFF
Global_Model
Remove CYCLIC commands,
Add SHPP, OFF
Add CYCLIC,,,,’CYCLCIC’
Move Coord System to Top
Find Max Node and
Cosines (PRVECT)
Local_Model, using
SLICE, single part
Define Crack
Move Coord to Top
Remove all other Tables
FRANC3D
Interface_Section
SIF
ANSYS:
1. Create model in Workbench
a. Set up coordinate systems
b. Name parts as GLOBAL_MODEL, LOCAL_MODEL, and INTERFACE
c. Add Temperatures, Pressures, Forces, Contacts, etc.
d. Add Boundary Conditions
e. Use consistent Units
2. Link ADPL to Setup of Structural Model
a. Edit Mechanical in ADPL (This will launch ANSYS Classic)
3. In Ansys Classic the following commands (with potential modifications) will be needed
to create the CDB files or add commands to the Workbench Mechanical Setup:
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ANSYS CLASSIC APDL CLICKS/COMMANDS:
SelectEverything
CDWRITE,DB,F3D_FULL_MODEL,CDB
CMSEL,U,LOCAL_MODEL
NSLE
CDWRITE, DB,F3D_GLOBAL_MODEL,CDB
CMSEL,,LOCAL_MODEL
NSLE
CDWRITE, DB,F3D_LOCAL_MODEL,CDB
ANSYS WORKBENCH ADPL COMMNADS:
ALLSEL,ALL,ALL
CDWRITE,DB,D:\ F3DMODELS\DOVETAIL\F3D_FULL_MODEL,CDB
ALLSEL,ALL,ALL
CMSEL,U,LOCAL_MODEL
NSLE
CDWRITE,DB,D: \F3DMODELS\DOVETAIL\F3D_GLOBAL_MODEL,CDB
ALLSEL,ALL,ALL
CMSEL,,LOCAL_MODEL
NSLE
CDWRITE,DB,D:\ F3DMODELS\DOVETAIL\F3D_LOCAL_MODEL,CDB
ALLSEL,ALL,ALL
GLOBAL MODEL FILE EDITS:
The following was changed in the GLOBAL_MODEL.CDB file:
1. REMOVED the following lines in the CDB file:
*DIM,_CYCLICMAP ....
*SET,_CYCLICMAP ....
CYCL,CDWR ....
2. ADDED the following Element Shape Checking Command:
SHPP,OFF
3. ADDED the following lines in the CDB file before the /GO and /FINISH Commands:
CYCLIC,,,,'CYCLIC'
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