ABAQUS

Tutorial

Version 6

Fracture Analysis Consultants, Inc

www.fracanalysis.com

Revised: November 2011

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Table of Contents:

1.0 Introduction .......................................................................................................................... 4

2.0 Tutorial 1: Crack Insertion and Growth in a Cube .............................................................. 4 2.1 Step 1: Creating the ABAQUS Model ............................................................................ 5

Step 1.1: Open ABAQUS Sketcher ........................................................................................ 5 Step 1.2: Create square in Sketcher ........................................................................................ 6 Step 1.3: Extrude square to make cube ................................................................................... 7

Step 1.4: Define material ........................................................................................................ 7 Step 1.5: Create Section .......................................................................................................... 8 Step 1.6: Assign Section to cube............................................................................................. 8 Step 1.7: Create Instance......................................................................................................... 9

Step 1.8: Create Step ............................................................................................................... 9 Step 1.9: Set field output ......................................................................................................... 9

Step 1.10: Apply pressure load ............................................................................................... 9 Step 1.11: Apply constraints ................................................................................................. 10

Step 1.12: Set mesh type ....................................................................................................... 10 Step 1.13: Set element type ................................................................................................... 10 Step 1.14: Subdivide edges ................................................................................................... 10

Step 1.15: Mesh the volume.................................................................................................. 11 Step 1.16: Create Job ............................................................................................................ 11

Step 1.17: Submit Job for analysis ........................................................................................ 12 Step 1.18: Save files .............................................................................................................. 12

2.2 Step 2: Reading ABAQUS FE Model into FRANC3D ................................................ 13

Step 2.1: Reading ABAQUS FE Model ............................................................................... 13

Step 2.2: Select the Retained Items in the FE Model ........................................................... 14 Step 2.3: Importing and Displaying the Local FE Model ..................................................... 15

2.3 Step 3: Insert a Crack ..................................................................................................... 17

Step 3.1: Select Cracks from FRANC3D Menu ................................................................... 17 Step 3.2: Select Crack Type .................................................................................................. 17

Step 3.3: Specify the Crack Size ........................................................................................... 18 Step 3.4: Specify Crack Location and Orientation ............................................................... 19

Step 3.5: Specify Crack Front Template Parameters ............................................................ 19 Step 3.6: Surface and Volume Meshing of Local Model after the Crack Insertion.............. 20

2.4 Step 4: Static Crack Analysis ........................................................................................ 21 Step 4.1: Select Static Crack Analysis .................................................................................. 21 Step 4.2: Select FE Solver .................................................................................................... 22

Step 4.3: Select ABAQUS Analysis Options ....................................................................... 23 2.5 Step 5: Compute Stress Intensity Factors ...................................................................... 24

Step 5.1: Re-Open FRANC3D restart file ............................................................................ 24 Step 5.2: Select Compute SIFs.............................................................................................. 24

2.6 Step 6: Manual Crack Growth ....................................................................................... 26 Step 6.1: Select Grow Crack ................................................................................................. 26 Step 6.2: Specify Growth Rate.............................................................................................. 26 Step 6.4: Specify Fitting and Extrapolation .......................................................................... 27

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Step 6.5: Specify Crack Front Template ............................................................................... 28

2.7 Step 7: Automatic Crack Growth .................................................................................. 28 Step 7.1: Open FRANC3D Restart File ................................................................................ 29 Step 7.2: Select Crack Growth Analysis ............................................................................... 29

Step 7.3: Specify Growth Parameters ................................................................................... 29 Step 7.4: Specify Growth Model Data .................................................................................. 30 Step 7.5: Specify Fitting and Template Parameters .............................................................. 31 Step 7.6: Specify Extension or Cycle Data ........................................................................... 31 Step 7.7: Specify Analysis Code ........................................................................................... 32

Step 7.8: Specify Analysis Options ...................................................................................... 33 3.0 Tutorial 2: Center Through-Crack in a Plate Sub-Domain ................................................ 35

3.1 Step 1: Create the Uncracked Model Using ABAQUS................................................. 35 Step 1.1: Create ABAQUS Model Database ........................................................................ 35

Step 1.2: Sketch a rectangle .................................................................................................. 36 Step 1.3: Extrude rectangle to make plate ............................................................................ 36

Step 1.4: Define material properties ..................................................................................... 36 Step 1.5: Define section ........................................................................................................ 37

Step 1.6: Assign section ........................................................................................................ 37 Step 1.7: Subdivide edges ..................................................................................................... 37 Step 1.8: Set mesh type ......................................................................................................... 37

Step 1.9: Mesh volume ......................................................................................................... 38 Step 1.10: Instance Assembly ............................................................................................... 38

Step 1.11: Create Job ............................................................................................................ 38 Step 1.12: Write Input ........................................................................................................... 39 Step 1.13: Create global orphan mesh .................................................................................. 39

Step 1.14: Create local orphan mesh..................................................................................... 39

Step 1.15: Edit global orphan mesh ...................................................................................... 39 Step 1.16: Edit local orphan mesh ........................................................................................ 40 Step 1.17: Create cut-surface node sets ................................................................................ 40

Step 1.18: Create Load Step.................................................................................................. 41 Step 1.19: Apply pressure load ............................................................................................. 41

Step 1.20: Apply constraints ................................................................................................. 42 Step 1.21: Create Job ............................................................................................................ 43

Step 1.22: Write Input ........................................................................................................... 43 Step 1.23: Save Model .......................................................................................................... 43

3.2 Step 2: Reading ABAQUS FE Model into FRANC3D ................................................ 43 Step 2.1: Read the ABAQUS FE model ............................................................................... 44 Step 2.2: Selecting the Retained Items in the local FE model .............................................. 44

3.3 Step 3: Insert a Crack .................................................................................................... 46 Step 3.1: Select New Flaw Wizard and Flaw Type .............................................................. 46

Step 3.2: Set Crack Size, Location and Template ................................................................. 46 2.5 Step 4: Static Crack Analysis ........................................................................................ 49

Step 4.1: Select Static Crack Analysis .................................................................................. 49 Step 4.2: Select FE Solver .................................................................................................... 49 Step 4.3: Select Analysis Options ......................................................................................... 49 Step 4.4: Merging Local/Global FE Models ......................................................................... 50

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3.4 Step 4: Compute Stress Intensity Factors and Grow Two Crack Fronts ....................... 52

Step 4.1: Re-Open FRANC3D restart file ............................................................................ 52 Step 4.2: Select Compute SIFs.............................................................................................. 52 Step 4.3: Select Grow Crack ................................................................................................. 53

Step 4.4: Set fitting, extrapolation and template parameters ................................................ 54 4.0 Tutorial 3: Automated Corner-Crack Growth in a Plate, with Crack Face Tractions ...... 56

4.1 Step 1: Create the Uncracked Model Using ABAQUS................................................. 56 Step 1.1: Create ABAQUS Model Database ........................................................................ 56 Step 1.2: Sketch a rectangle and extrude .............................................................................. 56

Step 1.3: Define material and section ................................................................................... 57 Step 1.4: Create Assembly .................................................................................................... 57 Step 1.5: Create Step ............................................................................................................. 57 Step 1.6: Apply boundary conditions.................................................................................... 58

Step 1.7: Mesh the volume.................................................................................................... 58 Step 1.8: Edit Model Keywords ............................................................................................ 59

Step 1.9: Run ABAQUS Analysis ........................................................................................ 59 Step 1.10: Save Model .......................................................................................................... 60

Step 1.11: Remove applied displacements and save file ...................................................... 60 4.2 Step 2: Read ABAQUS FE Model into FRANC3D ..................................................... 60

Step 2.1: Read the ABAQUS Mesh ...................................................................................... 60

Step 2.2: Select the Retained Items in the Local FE Model ................................................. 61 4.3 Step 3: Insert a Crack .................................................................................................... 62

Step 3.1: Select New Flaw Wizard and Flaw Type .............................................................. 62 Step 3.2: Set Crack Size, Location and Template ................................................................. 62

4.4 Step 4: Static Crack Analysis ........................................................................................ 65

Step 4.1: Run ABAQUS Static Analysis .............................................................................. 65

Step 4.2: Compute SIFs ........................................................................................................ 65 4.5 Step 5: Apply Crack Face Traction ............................................................................... 66

Step 5.1: Read the ABAQUS FE Model and Select Retained Items .................................... 66

Step 5.2: Insert Crack ............................................................................................................ 66 Step 5.3: Apply Crack Face Traction .................................................................................... 66

Step 5.4: Run ABAQUS Static Analysis .............................................................................. 67 Step 5.5: Compute SIFs ........................................................................................................ 68

4.6 Step 4: Automated Crack Growth Analyses ................................................................. 70 Step 6.1: Run ABAQUS Crack Growth Analysis ................................................................ 70

4.7 Step 7: Extract SIF History ........................................................................................... 74 Step 7.1: Select Create Growth History ................................................................................ 75 Step 7.2: Select SIF History .................................................................................................. 75

4.8 Step 8: Multiple Load Cases ......................................................................................... 76 Step 8.1: Read FE Model and Insert Crack........................................................................... 76

Step 8.2: Apply Crack Face Traction .................................................................................... 76 Step 8.3: Run ABAQUS Static Crack Analysis ................................................................... 77 Step 8.4: Compute SIFs ........................................................................................................ 77

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1.0 Introduction

This manual contains tutorials that introduce the modeling capabilities available through the

interface of FRANC3D Version 6 and ABAQUS Version 6.10 (or later). The first tutorial

describes a simple model where the entire domain is remeshed during crack insertion and crack

growth. The second tutorial describes a model where only a local subdomain is remeshed during

crack insertion and growth. This tutorial provides somewhat more detailed instructions for the

ABAQUS portion because of the increased modeling effort. The third tutorial describes the

process of applying crack face tractions along with the process of automated crack growth. It is

intended that the user perform the operations as they are presented, but you should feel free to

experiment and consult the other reference documentation whenever necessary.

Menu and dialog box button selections are indicated by bold text, such as File. Model and

corresponding file names will be indicated by italic text. Window regions and dialog options,

fields and labels will be underlined.

2.0 Tutorial 1: Crack Insertion and Growth in a Cube

This tutorial contains an example for FRANC3D with ABAQUS 6.10. The capabilities of the

program are illustrated by analyzing a surface crack in a simple (cube) component. Note that the

ABAQUS CAE user interface often changes with each new release, so the images of icons or the

menu layout might be different if you are using later versions (e.g. 6.11). Older versions of

ABAQUS are supported by FRANC3D, but you might have to translate our ABAQUS

modeling instructions.

First, all the steps needed to create the model geometry using ABAQUS are briefly described. It

is assumed that the user is somewhat familiar with ABAQUS. Once the model is created in

ABAQUS, the FRANC3D steps necessary to read the mesh information, insert a crack, rebuild

the mesh, perform the ABAQUS analysis, and compute stress intensity factors are described.

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Note that ABAQUS often provides several different ways to access menu and dialog entries; you

can use your favorite shortcuts or follow the tutorial.

2.1 Step 1: Creating the ABAQUS Model

First, we create a cube model using ABAQUS. We assume that the user knows how to use

ABAQUS, but we provide enough details in the steps below for a novice user to create the

simple cube model.

Step 1.1: Open ABAQUS Sketcher

Start with the ABAQUS graphical user interface (ABAQUS CAE). In the Module list

located under the toolbar (Fig 2.1), select Part to access the Part Module:

; this is the default when you start ABAQUS CAE 6.10. From the main

menu (the top menu bar), select Part and then select Create (or select Create from the Part

Manager dialog, or alternatively right-click on Parts in the model tree window and select

Create). The Create Part dialog box will appear (Fig 2.2); provide a name (e.g. cube) and

set Approximate size to 10. The Modeling Space should be 3D, the Type should be

Deformable and the Shape should be Solid. Select Continue and a grid will be displayed

in the main CAE window this is the Sketcher Window.

Figure 2.1: ABAQUS CAE 6.10 tool bar and main menu.

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Step 1.2: Create square in Sketcher

The cube is created by first creating a square in the Sketcher Window. Select the Rectangle

tool from the toolbar on the left side of the Sketcher Window, and create a square that

goes from (-1,-1) to (1,1) (you can start at any of the four corners). The part should appear as

in Fig 2.3.

Figure 2.2: Create Part dialog.

Figure 2.3: ABAQUS Sketcher with a square

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Step 1.3: Extrude square to make cube

Click on the red X or use the middle mouse button to click in the Sketcher Window so that

the Done button appears in the lower prompt area:

. The Edit Base Extrusion window will be

presented after pressing Done (Fig 2.4); enter 2 for the depth and select OK. The square will

be extruded to create a cube.

Figure 2.4: Edit Base Extrusion dialog.

Save the model by selecting File and Save As. Enter a file name (e.g. cube) and select OK

to save the .cae file.

Step 1.4: Define material

From the Module list, select Property . From the main menu, select

Material and then select Create; or select the Create Material icon. The Edit

Material dialog box is displayed (Fig 2.5). Provide a name for the material (e.g. steel) and

then select Mechanical Elasticity Elastic from the list. Enter values for the Youngs

modulus and Poisson ratio (e.g. 10000 and 0.3) and select OK.

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Step 1.5: Create Section

From the main menu, select Section and Create; or select the Create Section icon. The

Create Section dialog will be presented; enter a name for the section (e.g. cube_section) and

select Continue. The Edit Section window is displayed next. The Material should be the

material created in Step 5 (e.g. steel). Select OK to finish.

Figure 2.5: Edit Material dialog.

Step 1.6: Assign Section to cube

Assign the section properties to the cube by selecting Assign from the main menu and then

Section from the available options. Move the mouse over the cube and click the left mouse

button. Select Done from the lower prompt area once the cube has been highlighted. The

Edit Section Assignment window is displayed; select OK to finish.

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Step 1.7: Create Instance

From the Module list, select Assembly. From the main menu, select Instance and select

Create. The Create Instance window is displayed, select OK to finish.

Step 1.8: Create Step

From the Module list, select Step. From the main menu, select Step and Create. The

Create Step window is displayed, provide a name (e.g. CubeLoad) and choose Static,

General and select Continue... The Edit Step window is then displayed. Type in a

description of the loading and select OK to finish. (You can examine the other tabs and

fields at your leisure.)

Step 1.9: Set field output

The default ABAQUS output is okay, but if you want to see which results are available

follow these steps. From the main menu, select Output and then Field Output Requests

and then Manager. The Field Output Requests Manager window is displayed. Click on the

cell labeled Created and select Edit from the right side to view the output options. Select

OK or Cancel to close the Edit dialog and then select Dismiss to finish with the Output

Request Manager.

Step 1.10: Apply pressure load

From the Module list, select Load. From the main menu, select Load and Create. The

Create Load window is displayed. Provide a name and choose Pressure and select

Continue. Pick the top surface of the cube and select Done from the lower prompt area.

The Edit Load window is displayed; set the uniform pressure magnitude to be -1.0. The

resulting model should appear as in Fig 2.6; the symbols for the boundary conditions are

shown.

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Step 1.11: Apply constraints

From the Module list, select Load (if you changed modules after Step 11). From the main

menu, select BC and then select Create. The Create Boundary Condition window is

displayed. Provide a name and choose Symmetry/Antisymmetry/Encastre and select

Continue. Pick the bottom face of the cube and select Done from the lower prompt area;

you will need to rotate the model to see the bottom face. The Edit Boundary Condition

window will be presented, choose PINNED and select OK. The boundary condition

symbols are shown on the model.

Step 1.12: Set mesh type

From the Module list, select Mesh. Choose Part from the Object list:

. Alternatively, you can create an independent instance

in Step 8. Structured hexahedral meshing is the default, but if you want to make sure, follow

these steps. From the main menu, select Mesh and then Controls. The Mesh Controls

window is displayed. Choose Hex and Structured and select OK to finish.

Step 1.13: Set element type

From the main menu, select Mesh and then select Element Type. The Element Type dialog

is displayed; leave Standard for Element Library, choose Quadratic for Geometric Order

and leave 3D Stress for the Family. Select OK to finish.

Step 1.14: Subdivide edges

From the main menu, select Seed and then select Part. Leave the default Approximate

global size at 0.2 and select OK to finish.

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Step 1.15: Mesh the volume

From the main menu, select Mesh and then select Part. Select Yes from the command

prompt area to the question: "Ok to mesh the part?". The part will be meshed with brick

elements, Fig 2.7.

Step 1.16: Create Job

From the Module list, select Job. From the main menu, select Job and Create. The Create

Job dialog is displayed; provide a job name (cube_in_tension for example) and select

Continue. The Edit Job window is displayed. Type in a description and select OK to finish.

(You can peruse the other tabs and fields at your leisure.)

Figure 2.6: ABAQUS cube with boundary conditions

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Figure 2.7: ABAQUS brick mesh for a cube

Step 1.17: Submit Job for analysis

From the main menu, select Job and Manager. The Job Manager window is displayed.

Select Submit on the right side. The analysis will start and should complete successfully.

Select the Results option on the right side to view the results.

Step 1.18: Save files

Save the model using the File and Save As menu options. Note that a number of files will be

created automatically as ABAQUS runs. Included in the set of files should be an .inp file

with the job name as the prefix. This is the file that will be read by FRANC3D. This initial

analysis provides baseline results and ensures that we have created a correct model.

Note that the purpose of Steps 1.17 and 1.18 is not merely to create the .inp file that

FRANC3D requires, but to perform an analysis and look at the results to make sure the

displacement and stress results are as expected. You can skip these steps and simply Write

Input by right-clicking on the job name under Analysis and Jobs in the model tree window.

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Dont forget to save the .cae model file in case you wish to return to this model and modify

properties, etc. You can Exit from ABAQUS CAE now.

2.2 Step 2: Reading ABAQUS FE Model into FRANC3D

We start with an existing mesh for FRANC3D. We use the .inp file created by ABAQUS in the

previous step.

Step 2.1: Reading ABAQUS FE Model

Start with the FRANC3D graphical user interface, Fig 2.8, and select File and Open. Switch

File Filter in the Open Model File window, Fig 2.9, to Abaqus Files (*.inp) and select the file

name for the model, called cube.inp here, and then select Accept.

Figure 2.8: FRANC3D graphical user interface

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Figure 2.9: Open Model File dialog box

Step 2.2: Select the Retained Items in the FE Model

The next set of wizard panels allows you to choose the data that will be retained from the

ABAQUS .inp file, in addition to the nodes and elements. The first panel, Fig 2.10, lets you

choose to select all or individual items, choose selected items and select Next to get to the

panel shown in Fig 2.11. We will retain all the material and boundary conditions as this is a

full-model; both the material and boundary conditions will be transferred to the new mesh

once the crack is inserted. Select Finish.

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Figure 2.10: ABAQUS Model retain wizard panel.

Figure 2.11: Select items to retain wizard panel.

Step 2.3: Importing and Displaying the Local FE Model

The model will be read and displayed in the FRANC3D modeling window. You can turn on

the surface mesh and manipulate the view (see Section 2.1 of the FRANC3D Reference

guide for more details). The model should appear as in Figs. 2.12 and 2.13, which shows that

the mesh on the upper and lower surfaces is retained because we chose to retain all the

boundary conditions.

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Figure 2.12: ABAQUS model converted to FRANC3D showing retained facets on the pressure

surface at the top of the cube.

Figure 2.13: ABAQUS model converted to FRANC3D showing retained facets on the bottom

fixed surface.

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2.3 Step 3: Insert a Crack

We will now insert a half-penny surface crack into the model.

Step 3.1: Select Cracks from FRANC3D Menu

From the FRANC3D menu, select Cracks and New Flaw Wizard. The first panel of the

wizard should appear as in Fig 2.14. The default flaw type is Crack (zero volume flaw) and

this is what we want, so select Next. Note that you can choose to Save to file and add flaw;

this saves the flaw to a .crk file before adding it to the model.

Figure 2.14: New flaw wizard first panel to choose flaw type.

Step 3.2: Select Crack Type

The next panel of the wizard, Fig 2.15, allows you to choose the type of crack. The default

shape is the ellipse, which is what we want, so select Next.

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Figure 2.15: Flaw wizard panel to choose crack shape type

Step 3.3: Specify the Crack Size

The next panel of the wizard, Fig 2.16, allows us to specify the size of the ellipse. Enter 0.2

for both a and b and select Next.

Figure 2.16: Flaw wizard panel to set size of ellipse

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Step 3.4: Specify Crack Location and Orientation

The next panel of the wizard, Fig 2.17, allows you to specify location and orientation of the

flaw. Enter 90 for the 1st Rotation Angle and set the rotation axis to X and set the Z axis

Translation to 2. The flaw is displayed along with the model and should appear as in Fig

2.17; select Next when ready.

Figure 2.17: Flaw wizard panel to set location and orientation

Step 3.5: Specify Crack Front Template Parameters

The next panel of the wizard, Fig 2.18, allows you to specify the crack front template

parameters. We will leave all values at their defaults; select Finish when ready.

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Figure 2.18: Flaw wizard panel to set crack front template parameters

Step 3.6: Surface and Volume Meshing of Local Model after the Crack Insertion

The program begins the process of inserting the flaw into the original model and then meshes

the resulting cracked model. The progress of the operations is displayed on the screen, Fig

2.19. When the meshing is completed, the Flaw Insertion Status window will disappear and

the meshed cracked model will be displayed, Fig 2.20. Note that the mesh that is generated

will have about 16,500 elements.

Figure 2.19: Flaw Insertion Status window

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Figure 2.20: Meshed model with crack

2.4 Step 4: Static Crack Analysis

We will now perform the stress analysis using ABAQUS.

Step 4.1: 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 2.21. We will specify the file name for the FRANC3D

database first. We called it cracked_cube.fdb here; select Next once you enter a File Name.

Note that you must not overwrite the initial uncracked .inp file.

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Figure 2.21: Static Analysis wizard first panel File Name

Step 4.2: Select FE Solver

The next panel of the wizard, Fig 2.22, allows you to specify the solver; choose ABAQUS

and select Next (not shown in Fig 2.22).

Figure 2.22: Static Analysis wizard second panel solver

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Step 4.3: Select ABAQUS Analysis Options

The next panel of the wizard, Fig 2.23, allows you to specify the ABAQUS output and

analysis options. We want to use all quadratic elements, we do not have nodal temperatures,

and the model is a full-model and will not be combined with a global model, so uncheck the

Connect to global model and select Finish. FRANC3D will write files and then attempt to

execute ABAQUS based on the ABAQUS Batch /Executable information, Fig 2.23

Figure 2.23: Static Analysis wizard third panel ABAQUS output options

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Special Note: if ABAQUS fails to run, check the FRANC3D terminal window as well as the

ABAQUS .dat and .msg files for possible errors. Note that the ABAQUS Batch/Executable

information can be saved in the FRANC3D Preferences under the Edit menu.

2.5 Step 5: Compute Stress Intensity Factors

We will now compute the stress intensity factors for this crack. If you were able to run

ABAQUS from FRANC3D, then the model and the results should be ready, and you can skip to

Step 5.2.

Step 5.1: Re-Open FRANC3D restart file

From the FRANC3D menu, select File and Open. Choose the cracked_cube.fdb file, and

select OK. Note that if you closed the previous model or restarted FRANC3D, you can start

from this step.

Step 5.2: Select Compute SIFs

From the FRANC3D menu, select Cracks and Compute SIFs. The Stress Intensity Factor

wizard is displayed, Fig 2.24. 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. When you select Finish, the SIFs Plot window is displayed, Fig

2.25. You can view the three stress intensity factor (SIF) modes and export the data.

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Figure 2.24: Compute SIFs panel

Figure 2.25: Stress Intensity Factor plot dialog

Note that the SIF values are computed at the element midpoints along the crack front, and the

curves are plotted from A to B based on a normalized crack front position.

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2.6 Step 6: Manual Crack Growth

We can manually propagate the crack at this stage, and we 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.

Step 6.1: Select Grow Crack

From the FRANC3D menu, select Cracks and Grow Crack The Growth Parameters

wizard panel shown in Fig 2.26 is displayed. We switch the Growth Type to Quasi-Static for

this model and select Next.

Figure 2.26: First wizard panel for growth parameters

Step 6.2: Specify Growth Rate

In the second panel, Fig 2.27, the default value of n is 2.0; leave this and select Next.

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Figure 2.27: Second wizard panel for growth parameters

Step 6.4: Specify Fitting and Extrapolation

The next panel shown in Fig 2.28 allows you to specify the crack front point fitting

parameters. We set the median extension to 0.02, and specify a fixed order polynomial fit

with order set to 3 and extrapolation set to 3% at both ends of the crack front. Select Next.

Figure 2.28: Crack growth wizard panel for crack front fitting options

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Step 6.5: Specify Crack Front Template

The final panel, Fig 2.29, allows you to specify the crack front mesh template parameters.

We set the template radius to 0.025. Select Next to proceed with growing the crack and

remeshing.

Figure 2.29: Crack growth wizard panel for mesh template options

The resulting new mesh model can be analyzed as was done for the initial crack (see Step 4

above). Note that you will want to give this model a different name, perhaps cube_step_1, so

that you dont overwrite the initial crack model files. Automated crack growth analyses are

described next.

2.7 Step 7: Automatic Crack Growth

This section describes the steps taken to do automatic crack growth starting from the initial crack

model. We will start with an existing FRANC3D model. We will use the model created in

Sections 2.2 and 2.3.

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Step 7.1: Open FRANC3D Restart File

Start with the FRANC3D graphical user interface (see Fig 2.8) and select File and Open and

choose the file name specified in Section 2.3, called cracked_cube.fdb here. Click Accept.

The model will be read into FRANC3D (along with the results files that were created in

Section 2.3). We will ignore the fact that we already analyzed and propagated the initial

crack for now and proceed with setting up the automatic crack growth analysis.

Step 7.2: 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 2.30; it allows you to choose the method for computing

SIFs. We will leave all the default values. Select Next to display the second panel.

Figure 2.30: Crack Growth Analysis wizard first panel.

Step 7.3: Specify Growth Parameters

The second panel of the wizard should appear as in Fig 2.31. We set the growth type to

Quasi-Static for simplicity. All other values are left as defaults; select Next.

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Figure 2.31: Crack Growth Analysis wizard second panel.

Step 7.4: Specify Growth Model Data

The third panel of the wizard should appear as in Fig 2.32. We set the value of n to 2 for the

quasi-static crack growth and then select Next.

Figure 2.32: Crack Growth Analysis wizard third panel.

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Step 7.5: Specify Fitting and Template Parameters

The fourth panel of the wizard should appear as in Fig 2.33. We set the value for the

template radius to 0.02. The extrapolation could be increased from 3 to 5%, but 3% should

suffice for the first 5 steps that we will run here. Select Next.

Figure 2.33: Crack Growth Analysis wizard fourth panel.

Step 7.6: Specify Extension or Cycle Data

The fifth panel of the wizard should appear as in Fig 2.34. We will try growing the crack for

5 steps using a Constant Median Crack Growth Increment of 0.02. Select Next.

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Figure 2.34: Crack Growth Analysis wizard fifth panel.

Step 7.7: Specify Analysis Code

The sixth panel of the wizard should appear as in Fig 2.35. We will use ABAQUS and the

current crack growth step is 1 as we are starting from the initial crack. This process will

reanalyze the initial crack and name the files as cracked_cube_STEP_001. Typically we

would analyze the initial crack using a Static Analysis, grow the crack using Grow Crack,

and then start the automatic Crack Growth Analysis. The user can choose whether to start

the numbering from _STEP_001 or other. Subsequent file names will have their step number

incremented as the automatic analysis proceeds.

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Figure 2.35: Crack Growth Analysis wizard sixth panel.

Step 7.8: Specify Analysis Options

The seventh panel of the wizard should appear as in Fig 2.36. Some of the options will be

specific to your site. We will transfer all the boundary conditions, so leave the Transfer all

retained bcs checked. Click Next.

FRANC3D will save the fdb/inp files with the name cracked_cube_STEP_001 for the first crack

model and then ABAQUS will start 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). We will illustrate SIF history extraction

and fatigue life computations in Section 4.7.

34

Figure 2.36: Crack Growth Analysis wizard seventh panel.

35

3.0 Tutorial 2: Center Through-Crack in a Plate Sub-

Domain

In this tutorial, we provide the steps to complete a global/local crack growth analysis using

FRANC3D and ABAQUS. This analysis technique exploits the fact that the cracked region of a

model (local model) is generally small compared to the entire model (global model) by

minimizing the part of the model that undergoes remeshing during crack insertion and growth.

For this approach, global and local models will be created in ABAQUS; only the local model

will be remeshed in FRANC3D. The tutorial is divided into 4 major steps:

1. Create the uncracked global/local geometry and mesh using ABAQUS;

2. Import the local model to FRANC3D for crack insertion and remeshing;

3. Run a static crack analysis in ABAQUS using the full model;

4. Calculating fracture parameters and grow both crack fronts in FRANC3D.

Although it is not explicitly stated in the steps below, make sure to save your work throughout

the modeling process. In particular, save the .cae file at the end of Step 1. Also, it is assumed

that the user has some basic knowledge of ABAQUS. A new user is referred to Getting Started

with ABAQUS, which is part of the ABAQUS documentation.

3.1 Step 1: Create the Uncracked Model Using ABAQUS

We start by creating a simple plate model using ABAQUS.

Step 1.1: Create ABAQUS Model Database

Open the ABAQUS CAE and select Create Model Database. Create a new part named

cracked_part by clicking the icon in the Part Module and specifying the options shown

in Fig 3.1 (set approximate size to 200). Click Continue

36

Figure 3.1: Create part options

Step 1.2: Sketch a rectangle

When the Sketch Window appears, create a rectangle with dimensions: x = 20 and y = 50

with the bottom left corner at (0, 0).

Step 1.3: Extrude rectangle to make plate

Click Done at the bottom of the sketch window and Extrude to a depth of 5.

Step 1.4: Define material properties

Switch to the Property Module and select the icon to define the material properties;

Youngs Modulus is 2.0E6 and Poissons Ratio is 0.30. Click OK.

37

Step 1.5: Define section

Select the icon and define a Solid, Homogeneous section with the material created in the

previous step. Click Continue In the Edit Section window, click OK.

Step 1.6: Assign section

Select the icon and assign the section to the cracked_part by selecting it in the modeling

window. Click Done. In the Edit Section window, click OK.

Step 1.7: Subdivide edges

Expand cracked_part in the Model Tree (as shown in Fig 3.2) and double-click Mesh.

Select the icon to assign a global mesh seed size of 2. Click OK.

Figure 3.2: Model tree expanded under cracked part

Step 1.8: Set mesh type

Select the icon and specify quadratic hex elements (ABAQUS element type C3D20R).

Click OK. (Note that if linear elements are used, extra work is required of the user see

Step 22.)

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Step 1.9: Mesh volume

Select the icon to mesh cracked_part. Click Yes at the bottom of the Modeling

Window. The meshed cracked_part is shown in Fig 3.3.

Figure 3.3: Meshed plate model in ABAQUS

Step 1.10: Instance Assembly

Switch to the Assembly Module and select the icon to instance cracked_part. Click

OK in the Create Instance window.

Step 1.11: Create Job

Switch to the Job Module and select the icon to create a job. Name the job orphan and

click Continue Click OK in the Edit Job window.

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Step 1.12: Write Input

Select the icon to display the Job Manager. Select orphan and click Write Input at the

right. Click Dismiss.

Special Note: ABAQUS doesnt allow creation of node sets from a part created in CAE. We

need some node set definitions to inform FRANC3D which surfaces will be used to glue the

local model back into the global model so that the mesh on those surfaces will remain unaltered.

So, we must now read in the orphan mesh created in the previous steps to define the local and

global models.

Step 1.13: Create global orphan mesh

From the File menu, select Import and Model and then select orphan.inp. Click OK. A

new model is created in the Model Tree at the left. Right click on the orphan model and

select Copy Model and name the new model global. Click OK.

Step 1.14: Create local orphan mesh

Repeat the previous step and name the copied model local. Click OK.

Step 1.15: Edit global orphan mesh

Switch to the Mesh Module, global Model, and Object: Part at the top of the modeling

window and select Mesh and Edit from the upper toolbar. In the Edit Mesh window, select

Element in the Category region and select Delete in the Method region.

Special Note: since the global model region is being defined first, the portion of the model that

will be used for local crack insertion needs to be deleted first.

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As shown in Fig 3.4, select the portion of the model that corresponds to the local model,

leaving only the global portion unselected (most easily done by viewing the 1-2 plane). At

the bottom of the Modeling Window, with Delete associated unreferenced nodes selected,

click Done. Switch to the Assembly Module, which will automatically regenerate the

instance.

Figure 3.4: Selection of local portion of the model to be deleted

Step 1.16: Edit local orphan mesh

Repeat the previous two steps for the local model with the exception of deleting exactly the

opposite of what was deleted in the global model.

Step 1.17: Create cut-surface node sets

In the Model Tree, expand the local model as shown in Fig 3.5 and double-click Sets to

create a node set named Cut_Surf_Local, which will define the local surface that merges the

local model to the global model. Any sets that already exist can be ignored. Click

Continue

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Special Note: if you use linear elements, you must specify a Cut-Surf node set for the local AND

for the global model; you will need to have these surfaces later in FRANC3D when merging the

cracked-local and global pieces together.

Select by angle in the drop-down selector at the bottom of the Modeling Window and then

gather the nodes on the top and bottom surface of local (hold down the shift key to continue

adding to selected nodes). Click Done.

Figure 3.5: Model tree expanded under local

Step 1.18: Create Load Step

Switch to the Step Module and global Model and click the icon to generate a load step.

The default values are ok, so click Continue and OK.

Step 1.19: Apply pressure load

Switch to the Load Module and global Model to begin applying loads and boundary

conditions. Select the icon and select Pressure in the Types for Selected Step region.

Click Continue. At the bottom of the Modeling Window, select by angle in the drop-down

menu and then select the top surface of the model as shown in Fig 3.6. Click Done. In the

Edit Load window, enter -10 in the Magnitude box and click OK.

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Figure 3.6: Loaded surface selection

Step 1.20: Apply constraints

Click the icon and rotate the model so that the bottom surface is visible. In the Create

Boundary Condition pop-up window enter: face_y for the Name, Step-1 for the step,

Mechanical in the Category region and Displacement/Rotation in the Types for Selected

Step region. Click Continue With by angle selected at the bottom of the Modeling

Window, select the bottom face of the model. Click Done. In the Edit Boundary

Condition window, select U2 and enter 0. Click OK.

Once again, click the icon. In the Create Boundary Condition window enter: point_xz

for the Name, Step-1 for the step, Mechanical in the Category region and

Displacement/Rotation in the Types for Selected Step region. Click Continue With

individual selected in the drop-down selector at the bottom of the Modeling Window, select

the middle node on the bottom face. Click Done. In the Edit Boundary Condition window,

select U1, U3 and enter 0 in both. Click OK.

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Step 1.21: Create Job

Switch to the Job Module and select the icon to create a job. With global highlighted,

name the job global and click Continue and OK. Repeat for local with local highlighted

in the Create Job window.

Step 1.22: Write Input

Select the icon to display the Job Manager. Select global and click Write Input at the

right. Repeat for local. Click Dismiss.

Step 1.23: Save Model

Before exiting ABAQUS CAE, save your work.

At this point in the tutorial, we have finished Step 1 in which the global and local portions of the

model have been defined. In the next step, we will use the local model for crack insertion and

remeshing in FRANC3D.

3.2 Step 2: Reading ABAQUS FE Model into FRANC3D

The next step is to read the local model into FRANC3D and insert a crack. We have saved the

two inp files as: local .inp and global .inp. Inside the local file, there is a node set called

Cut_Surf_Local that defines the nodes of the mesh facets in local that are to be retained.

If desired, copy the local .inp and global .inp files from the ABAQUS working directory to the

FRANC3D working directory. Typically a user will use one folder per model so the working

directory will be the same for both programs.

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Step 2.1: Read the ABAQUS FE model

Start FRANC3D and select File and Open. In the Open Model File window, choose the

Abaqus (*.inp) file filter and select local.inp file and Click OK.

Step 2.2: Selecting the Retained Items in the local FE model

Follow the wizard through the panels shown in Fig 3.7. We choose selected items and then

choose all materials and select mesh facets. We select the Cut_Surf_Local node set to be

retained. There are no boundary conditions on this local model. The resulting FRANC3D

model is shown in Fig 3.8.

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Figure 3.7: Wizard panels showing selections for local.inp

Figure 3.8: FRANC3D local.inp showing retained facets on top cut surface

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3.3 Step 3: Insert a Crack

We will now insert a quarter-penny corner crack into the model.

Step 3.1: Select New Flaw Wizard and Flaw Type

Insert the crack into this model by selecting Cracks and New Flaw Wizard. In the Flaw

Insertion window select Crack (zero volume flaw) and click Next. In the next wizard panel,

select the through-crack shape with two crack fronts (Fig 3.9).

Figure 3.9: Through-crack shape selected

Step 3.2: Set Crack Size, Location and Template

For the remaining wizard panels, follow Figs 3.9 through 3.12, which show the crack shape,

location, orientation and template parameters used for this crack. The Flaw Insertion

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Progress window will be displayed while inserting the crack and remeshing. The remeshed

cracked model is shown in Fig 3.13.

Figure 3.10: Through-crack dimensions

Figure 3.11: Through-crack location and orientation within the model

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Figure 3.12: Crack front template parameters

Figure 3.13: Meshed crack model

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The next step is to write the files for the cracked-local model and to perform the ABAQUS

analysis on the recombined cracked-local/global model.

2.5 Step 4: Static Crack Analysis

FRANC3D merges the local and global models and subsequently calls ABAQUS to perform the

analysis. The following steps describe the procedure for merging these two portions followed by

the analysis of the resulting merged model.

Step 4.1: Select Static Crack Analysis

From the FRANC3D menu, select Analysis and Static Crack Analysis. Specify a file name

in the first wizard panel (e.g. cracked_plate). Click Next.

Step 4.2: Select FE Solver

Choose ABAQUS from the next wizard panel, Fig 3.14. Click Next.

Figure 3.14: Static Analysis wizard panel allows choice of analysis code

Step 4.3: Select Analysis Options

Choose to Connect to global model in the following wizard panel, Fig 3.15 and specify

global.inp as the Global model filename. Note that there are no boundary conditions on the

local model. All the boundary conditions from the original global model will be transferred

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to the recombined crack model as long as the Transfer retained bcs remains checked in Fig

3.15. Click Next.

Figure 3.15: Static Analysis wizard panel for ABAQUS output and analysis options

Step 4.4: Merging Local/Global FE Models

Choose to Merge nodes and choose the Cut_Surf_Local node set, Fig 3.16. Ignore the

Global node set/surface(s) to merge/constrain box (as long as you used second-order

elements). Click Finish to begin the ABAQUS analysis.

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Note that the final panel has a check-box that allows the user to write files without running

ABAQUS. This option allows the user to write the files and then edit them or transfer the files to

a different computer before running ABAQUS.

Figure 3.16: Static Analysis wizard panel for recombining the cracked-local and global pieces

When the ABAQUS analysis has completed, proceed to Step 4. The following files are created

by FRANC3D: cracked_plate.fdb, cracked_plate.inp, cracked_plate_full.inp, and

cracked_plate.txt. ABAQUS will generate a cracked_plate_full.fil file that contains the results,

which FRANC3D requires to compute SIFs. These files should not be deleted.

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3.4 Step 4: Compute Stress Intensity Factors and Grow Two Crack Fronts

We will now compute the stress intensity factors for this crack and grow one step. If you are

able to run ABAQUS from FRANC3D, then the model should be open in FRANC3D and the

displacement file will be read automatically, and you can skip to Step 4.2.

Step 4.1: Re-Open FRANC3D restart file

Transfer the ABAQUS generated .fil file to the working directory, if it is not there already

(e.g. if you ran on a different computer). Start FRANC3D and open the cracked_plate.fdb

file saved during Step 3. The cracked_plate_full.fil file should be read automatically.

Step 4.2: Select Compute SIFs

Select Cracks and Compute SIFs Leave all the defaults in the dialog box and select

Finish to view the plotted SIFs for the crack fronts. Note that there are two fronts so there

will be two plot windows. Look for the A-B on the model to determine which front is being

displayed, Fig 3.17.

Figure 3.17: Mode I stress intensity factor plot.

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Step 4.3: Select Grow Crack

From the FRANC3D menu, select Cracks and Grow Crack The Growth Parameters

wizard panels shown in Fig 3.18 and Fig 3.19 are displayed. In the first panel, we switch the

Growth Type to Quasi-Static for this model and select Next. In the second panel, the default

value of n is 2.0; leave this and select Next.

Figure 3.18: First wizard panel for growth parameters

Figure 3.19: Second wizard panel for growth parameters

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Step 4.4: Set fitting, extrapolation and template parameters

The next two panels shown in Fig 3.20 and Fig 3.21 allow you to specify the crack front

point fitting and mesh template parameters. We set the median extension to 0.3, and specify a

Fixed Order Polynomial fit with order set to 3 and extrapolation set to 3% at both ends of the

crack front. There are two crack fronts in this model, and the dialog in Fig 3.20 allows you

to specify the fitting options for each of the fronts. The crack front mesh template shown in

Fig 3.21 extends beyond the model surface, which is necessary. Select Next on this panel

when ready to proceed with the crack insertion and remeshing.

Figure 3.20: Crack growth panel for front fitting options. Note that the user can define fitting

options for each of the two crack fronts.

55

Figure 3.21: Crack growth panel for mesh template options.

The resulting new mesh model can be analyzed as was done for the initial crack (see Step 4

above). Note that you will want to give this model a different name, perhaps

cracked_plate_step_1, so that you dont overwrite the initial crack model files. Automated crack

growth analyses are described in Tutorial; you can return to this model to try automatic crack

growth.

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4.0 Tutorial 3: Automated Corner-Crack Growth in a

Plate, with Crack Face Tractions

In this tutorial, we describe the steps to complete an automated crack growth analysis using the

FRANC3D and ABAQUS interface, including the application of crack face tractions from an

uncracked ABAQUS stress analysis. For this tutorial, an initial uncracked model will be created

and analyzed in ABAQUS. The tutorial is divided into 8 major steps:

1. Create the uncracked geometry and mesh using ABAQUS;

2. Import the model to FRANC3D;

3. Insert a crack and remesh;

4. Run a static analysis and compute SIFs;

5. Apply the crack face tractions and static crack analysis;

6. Subsequent automatic crack growth analysis;

7. Extract SIF history; and

8. Static crack analysis with multiple load cases.

4.1 Step 1: Create the Uncracked Model Using ABAQUS

Start by creating a simple plate model using ABAQUS:

Step 1.1: Create ABAQUS Model Database

Open the ABAQUS CAE and select Create Model Database. Create a new part named

rectangular_bar by clicking the icon in the Part Module, specifying the name and

setting approximate size to 10. Click Continue to display the Sketch window.

Step 1.2: Sketch a rectangle and extrude

Create a rectangle starting at 0,0 with dimensions x=0.5 and y=1.0. Click the red X at the

bottom and click Done and specify 0.25 for the depth. A rectangular bar will be created (Fig

4.1).

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Figure 4.1: Rectangular bar geometry

Step 1.3: Define material and section

Define an elastic material with properties: E=10,000 and nu=0.3. Define the section and

assign the material to the section and attach to the geometry.

Step 1.4: Create Assembly

Create the Assembly, the mesh can be indepenedent.

Step 1.5: Create Step

Create the Step as a Static,General analysis load step.

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Step 1.6: Apply boundary conditions

Define the Loading using applied displacement. Define an applied displacement to the upper

surface with y-displacement=0.01. Define y-constraints on the bottom surface and then

define x-constraint for the edge shown as a red line in Fig 4.2, and fully constrain the point at

the origin by adding a z-constraint at that point.

Figure 4.2: Applied displacement and constraints

Step 1.7: Mesh the volume

Define the mesh using a mesh seed of 0.1 and using hexahedral elements. The resulting

mesh should appear as in Fig 4.3.

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Figure 4.3: Hexahedral mesh

Step 1.8: Edit Model Keywords

Before submitting the job for analysis, edit the Model keywords. Add the following lines

just before the *End Step:

** output displacements and stress to fil results file

*File Format, ASCII

*Node File, Frequency=1

U

*El File, position=averaged at nodes, Frequency=1

S

Step 1.9: Run ABAQUS Analysis

Submit the job for analysis. A .fil file will be created that contains the stress components at

the nodes. This is the data that is expected by FRANC3D when applying stress as crack face

60

tractions. Once the analysis has finished, you should verify that the deformation and stress

are correct. The stress should be 100.0 everywhere in the model.

Step 1.10: Save Model

You should save the model before proceeding.

Step 1.11: Remove applied displacements and save file

The purpose of this tutorial is to illustrate: 1) how to apply crack face tractions and 2) how to

perform automated crack growth analyses. We will save a model that has constraints, but no

loads so that we can apply the uncracked stress as crack face tractions and compare SIFs to

the case where only the far-field loads are applied. We can delete the boundary condition

that contains the applied y-displacement on the upper surface of the bar and then rewrite the

.inp file (without submitting the job for analysis).

We should now have two .inp files and a .fil file. We have named the original .inp and .fil file

applied_disp and have named the .inp file, created in step 1.11, no_disp.inp. We can now exit

ABAQUS CAE and proceed with FRANC3D.

4.2 Step 2: Read ABAQUS FE Model into FRANC3D

The next step is to read the model into FRANC3D and insert a crack.

Step 2.1: Read the ABAQUS Mesh

Copy the .inp files from the ABAQUS working directory to the FRANC3D working

directory if they are different. Start FRANC3D. Select File and Open. In the Open Model

File window, choose the ABAQUS FILES (*.inp) file filter and applied_disp.inp file and

Click OK.

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Step 2.2: Select the Retained Items in the Local FE Model

Follow the wizard through the panels shown in Fig 4.4. We choose selected items and then

choose all materials, all boundary conditions, and no mesh facets. The resulting FRANC3D

model is shown in Fig 4.5.

Figure 4.4: Wizard panels showing selections for applied_disp.inp

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Figure 4.5: Model showing retained facets for applied y-displacement on top surface.

4.3 Step 3: Insert a Crack

We will now insert a quarter-penny corner crack into the model.

Step 3.1: Select New Flaw Wizard and Flaw Type

Insert the crack into the model by selecting Cracks and New Flaw Wizard. In the Flaw

Insertion window select Crack (zero volume flaw), select the Save to file and add flaw

option, and click Next. In the following panel, select the ellipse crack shape.

Step 3.2: Set Crack Size, Location and Template

For the remaining wizard panels, follow Figs. 4.6 4.8, which show the crack shape,

location, orientation and template parameters used for this crack. The meshed crack model is

shown in Fig 4.9.

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Figure 4.6: Elliptical-crack dimensions

Figure 4.7: Crack orientation and location

64

Figure 4.8: Crack front template parameters

Figure 4.9: Crack model surface mesh

65

4.4 Step 4: Static Crack Analysis

Perform a static crack analysis on this model to compute the SIFs for far-field loading.

Step 4.1: Run ABAQUS Static Analysis

From the FRANC3D menu, select Analysis and Static Crack Analysis. Specify a file name

in the first wizard panel (e.g. corner_crack_bar). Click Next. Choose ABAQUS as the

solver. The elements should be second order. We do not connect to a global model. All

boundary conditions should be transferred. If the ABAQUS analysis fails to run to

completion, examine the .dat and .msg files along with the FRANC3D cmd window for

messages.

Step 4.2: Compute SIFs

Once the analysis finishes, compute the SIFs; they should be as in Fig 4.10.

Figure 4.10: Mode I SIFs for far-field applied displacement

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4.5 Step 5: Apply Crack Face Traction

In this step, we will start from the no_disp.inp ABAQUS file, apply crack face tractions using

the stress from the applied_disp.fil file, and compare the resulting SIFs with those from Step 4.

The first step is to read the no_disp.inp model into FRANC3D and insert a crack.

Step 5.1: Read the ABAQUS FE Model and Select Retained Items

Start FRANC3D (or close the existing model) and read the no_disp.inp file. Follow the

wizard panels in Fig 4.4 again as we want to retain all of the boundary conditions, which

should be constraints on the bottom surface only.

Step 5.2: Insert Crack

Insert the same crack as shown in Figs 4.6-4.8. If you saved the .crk file, you can read the

file using the Flaw From Files option in the Cracks menu.

Step 5.3: Apply Crack Face Traction

Once the cracked model has been meshed, we will apply the crack face traction. Select

Loads and Crack Face Pressure/Traction. Click on Add in the dialog box shown in Fig

4.11. Choose Residual Stress Defined on a Mesh and click on Next. Select the

applied_disp.inp and applied_disp.fil files and click on Next. There is only one set of results

in the .fil file so we click Finish and then Accept in the first dialog.

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Figure 4.11 Crack face tractions dialog.

Step 5.4: Run ABAQUS Static Analysis

Perform a static crack analysis on this model using ABAQUS. The elements should be

second order. All boundary conditions should be transferred and we must check the Apply

crack face tractions box, Fig 4.12. If the ABAQUS analysis fails to run to completion,

examine the .dat and .msg files along with the FRANC3D terminal window for messages.

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Figure 4.12: Mode I SIFs for crack face tractions using M-Integral

Step 5.5: Compute SIFs

Once the analysis finishes, compute the SIFs; they should be as in Fig 4.13. In the SIF

dialog, make sure that the Crack face traction box is checked if using the M-integral, Fig

4.14. We can compare the M-integral SIF values against the displacement correlation SIF

values to ensure that the results are consistent. If thermal or crack face traction terms are not

properly accounted for in the M-integral computations, the SIFs will differ greatly from the

displacement correlation SIFs. We can also compare these SIFs with those from applied far-

field loading, Fig 4.10; this is left as an exercise for the reader.

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Figure 4.13a: Mode I SIFs for crack face tractions using M-Integral

Figure 4.13b: Mode I SIFs for crack face tractions using Displacement Correlation.

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Figure 4.14: Compute SIFs dialog.

4.6 Step 4: Automated Crack Growth Analyses

In this step, we illustrate the process of automated crack growth starting from the initial crack

model in Section 4.3.

Step 6.1: Run ABAQUS Crack Growth Analysis

Continuing in FRANC3D with the existing model from Step 4.5, select Analysis and Crack

Growth Analysis. Follow the wizard panels in Figs 4.15-4.21. We will do 5 steps of crack

growth using ABAQUS as the solver and growing 0.01 units at each step (this is the growth

for the point along the crack front with the median Mode I SIF value crack growth at other

points along the front are scaled accordingly). When you select Finish on the final wizard

panel, the automated analyses should start by writing the ABAQUS input file, with the base

name and _STEP_1 appended. ABAQUS should then start in batch mode to solve the

current model (in this case, this is a repeat of the solution from Section 4.3). Once ABAQUS

finishes, FRANC3D reads the resulting fil file and grows the crack, remeshes, and writes out

the ABAQUS input files for the next step. This should continue for the specified 5 steps.

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Figure 4.15: Automated propagation first wizard panel

Figure 4.16: Automated propagation second wizard panel

72

Figure 4.17: Automated propagation third wizard panel

Figure 4.18: Automated propagation fourth wizard panel

73

Figure 4.19: Automated propagation fifth wizard panel

Figure 4.20: Automated propagation sixth wizard panel

74

Figure 4.21: Automated propagation seventh wizard panel

Once the 5 steps of automated crack growth are complete, you can read in the model and results

for any of the steps and compute SIFs. The SIF history can be extracted by computing and

exporting SIFs for each of the steps. The SIF history is contained in the FRANC3D restart files.

The next section describes the dialog boxes that can be used to display the SIF history.

4.7 Step 7: Extract SIF History

In this step, we illustrate the process of extracting SIF history data using the 5 steps of crack

growth complete in Section 4.6.

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Step 7.1: Select Create Growth History

Continuing in FRANC3D with the existing model from Section 4.4, select Advanced and

Create Growth History. The dialog shown in the left panel of Fig 4.22 will appear.

You can use the Plot menu to display the crack fronts, Fig 4.22 right panel. Close the

dialog boxes when you have examined them; consult the FRANC3D Reference

documentation for more details.

Figure 4.22: Create Growth History dialog and the six crack fronts displayed in the right panel.

Step 7.2: Select SIF History

From the FRANC3D main menu, select Fatigue and then SIF History to display the SIF

History dialog, Fig 4.23. This dialog allows you to select a path through the crack fronts,

plot the SIF along this path, and export this data for use in the fatigue life module. If you

have multiple crack fronts, you can choose the starting crack front id through the Settings

menu.

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Figure 4.23: SIF History dialog.

4.8 Step 8: Multiple Load Cases

In this step, we illustrate the analysis of multiple load cases. We will start from the

applied_disp.inp ABAQUS file, apply crack face tractions into a second load case using the

stress from the applied_disp.fil file, and then examine the resulting SIFs.

Step 8.1: Read FE Model and Insert Crack

The first step is to read the applied_disp.inp model into FRANC3D following the steps in

Section 4.2. We insert the same crack as in Section 4.2 and 4.3. If you saved the crack to a

file, you can insert this crack from the file using the Flaw From Filesoption from the

Cracks menu.

Step 8.2: Apply Crack Face Traction

Once the crack is inserted, we apply crack face tractions following the steps in Section 4.3

except that we change the Load Case number to 2, Fig 4.11.

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Step 8.3: Run ABAQUS Static Crack Analysis

We then perform a static crack analysis on this model, make sure that the Crack face traction

box is checked (see Fig 4.14 or 4.21). The ABAQUS .inp file that FRANC3D writes will

have two *Step data blocks and ABAQUS will generate results for both load cases.

Step 8.4: Compute SIFs

The Compute SIFs dialog will indicate that SIFs are available for two load cases, Fig 4.24.

We can select the first load case only and plot the SIFs, Fig 4.25, to verify that these are

correct. We can then select the second load case, Fig 4.26, and plot these SIFs, Fig 4.27.

Note that the second load case consists of the first load case displacement constraints and

applied displacements along with the applied crack face tractions. Thus, the mode I SIFs for

the second load case are double those from the first load case.

Figure 4.24: Compute SIFs dialog for multiple load case analyses - first load case checked

78

Figure 4.25: Mode I SIFs for the first load case using M-Integral

Figure 4.26: Compute SIFs dialog for multiple load case analyses - second load case checked

79

Figure 4.27: Mode I SIFs for the second load case using M-Integral

This is the end of the tutorial!