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Outline Mesh independent connection of two parts modeled with shell elements

Analysis type(s): Explicit, 3D analysis

Element type(s): Shell, tied

Materials law(s): Elastic, elastic-plastic

Model options: Boundary conditions, Nodal loads

Key results: Displacements, Tying force

Prepared by:

Date:

Wang Kunpeng, Pierre Culiere

February 2008

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Pre-processor, Solver and Post-processor used:

• Visual-Mesh: for generation of the geometry and meshes.

• Visual-Crash for PAM: to assign controls, material, load, constraints and time history data.

• PAM-CRASH (Explicit): to calculate the solution.

• Visual-Viewer: to evaluate the results for contour plots, deformations, etc.

Prior knowledge for the exercise:

No prior Visual or PAM-CRASH knowledge is required for working through this exercise.

Problem data and description:

Units: kN, mm, kg, ms, Kelvin

Description: Two steel plates are bonded with an adhesive. The model represents a lap joint tension test.

Both plates have the same size:

Length: 50 mm Width: 20 mm Thickness: 2 mm

The overlap is of 10 mm and corresponds to the bonding area.

Loading: Part 1 has one end fixed; part 2 is pulled with an imposed velocity.

Material: Steel material data: E=210 kN/mm2, ν=0.3 and density 7.8*10-6 kg/mm3). Adhesive: stiffness unknown.

Supplied datasets:

No datasets or meshes are needed to tackle the problem; the mesh will be generated as a part of the exercise.

It is recommended that you use the following names for the PAM-CRASH input and results files:

For the elastic Tied Model mesh use Tied_Elastic.pc

For the Elastic-Plastic Tied Model mesh use Tied_Elastic_Plastic.pc

In each case completed PAM-CRASH datasets are available in case you get into trouble.

PPaarrtt 11:: CCrreeaattee PPllaatteess iinn VViissuuaall MMeesshh This part of the tutorial is not detailed. If you need more guidance on meshing, please refer to Exercise 1 of this tutorial.

Start Visual Crash for PAM (VCP) and activate the Visual-Mesh context. The context bar is normally located on the left side of the screen.

Creating a New Model

Select File and option New then specify the model unit system:

Set Source Units to mm, kg, ms

Set Target Units to mm, kg, ms

Click OK

Planning and specifying nodal points

Plate 1 has four points in the x-y plane with one corner at the origin (x=0, y=0) and the other points having the coordinates shown; (z=0 for all points).

Defining the (corner) points

The four corner points are defined using the Node > By XYZ, Locate… panel.

Entered coordinates and click Create Node. Default node ID numbers are used.

For the four points, use z=0.

Generating the mesh surface

Go to 2D > 3/4 Point Mesh and choose the option 4 point polygon. Then click on the four corner nodes in sequence.

Generating the mesh of part 1

Click on Mesh and a new panel opens to control the mesh parameters: element sizes, type of mesh and connection (stitching) to adjacent meshes. Use a 5mm element size and click Create Mesh.

The mesh will appear; accept it by clicking OK and click Close to close the mesh panel.

Generating the mesh of part 2 by transforming part 1

1. Go to 2D>Transform

2. Select option Translation

3. Choose Offset in the pull-down menu

4. Click on Select Entities button

5. Select all elements of part 1

6. Input the exact offset value: dx=40, dy=0, dz=2. The 2 mm gap in Z between the shell parts corresponds to their thickness. The adhesive thickness is neglected.

7. Click on Update Entities ◊ you get a preview of the transformation

8. Choose Copy

9. Assign a new Part ID (2) to the new part

1. Click Copy to finish creating part 2

Saving and Ending the meshing work

The meshing work is now complete. It is probably wise to save the data with File > Save to a suitable folder with a suitable name. Export this as a filename.vdb file; which is the default name for a Visual Environment Database.

A suitable name could be “Tied_Elastic.vdb”.

Remark: Instead of File > Save, it is possible to use File > Export to save data in a solver input file format (.vdb) format. However, some of the information, like geometry data would be lost.

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This involves:

Starting Visual Crash PAM for creating the Tied Model.

Using VCP for defining:

• Boundary conditions on PART 1 (fixed end)

• Boundary conditions on PART 2 (velocity at end)

• Part and material data

• Control data

Starting Visual-Crash PAM

You may now duplicate the file of the model you just created. If things go wrong, it is possible to go back to this back-up file and start things again.

1. Copy Tied_Elastic.vdb to Tied_Elastic.vdb.backup (in Windows explorer or Linux shell)

2. Activate the Visual-Crash PAM context

Introduction to Tied Interfaces

A TIED interface is a mesh independent connection entity of the PAM-SCL solver library. It ties a set of slave nodes to master segments, here, elements. For this interface, the slave nodes can be positioned at a distance to the master surface.

Slave nodes are searched around a given master segment within a box delimited by a thickness of value hcont (the contact thickness) around the master segment.

Once a node is found to be slave to a segment, the solver uses penalty forces to keep the node at a fixed position relative to the segment.

Rupture: the tied may fail according to a simple rupture model defined with the RUPMO entity. A simple rupture model consists in setting maximum normal and tangential forces and using a criterion combining both values.

Generating the Tied Interface

1. In the explorer, go to Links>Tied and right click New

2. Click on the IPART value 0 (blue circle) for getting the Data Model Entities card

3. Click on NEW PART and it will be showed in highlight (step 3)

4. Click on OK button and value 0 will change into 3 (we have already created part 1 and part 2, so the software will create a successive value 3)

5. Change the NAME into TIED for simplifying.

6. Choose the Slave nodes:

• Choose the nodes as shown on part 2, or the entire part 2 if you want slave nodes to be found by proximity search (using a radius to be defined later)

• Click Update Selection or click the middle mouse key

• Node or part numbers appear in the card’s main body

7. Choose the Master elements:

• Select the Sel option as Ele (blue circle) or as Part.

• Choose the master elements as shown or the entire part 1 if you want an automatic search.

• Click Update Selection (highlighted in blue frame) ◊ element or part numbers appear in the card’s main body (brown frame)

8. Click on Apply button for finishing the TIED interface creation. The defined TIED interface should appear as follows.

Define the link search distance

In the explorer, go to Crash > Part > Tied and right click “Edit” on the tied you created

A panel pops up. In the panel set the following values:

• TCONT = 1.5 mm

• RDIST = 2

Click Apply then Close buttons.

Boundary conditions (fixed end and other constraints)

1. In the explorer, go to Crash > Loads > Displacements BC and right click “New”.

2. Select end nodes of PART 1 and click Update Selection or the middle mouse key. Selected nodes appear in a list.

3. Activate the required constraint: X, Y, Z for translational and U, V, W for rotational degrees of freedom. Choose “1”, meaning constrained, for all degrees of freedom

4. Choose an appropriate title for the constraint; e.g. “Fixed_End_of_PART1”

5. Save the condition with Apply and Close.

Loading conditions (at the opposite free end of PART 2)

The aim now is to apply positive (x) velocity loading at one free end of part 2.

1. In the explorer, go to Crash > Loads >3D BC and right click New to assign nodal velocity loads.

2. Select nodes at end in positive X- direction and click Update Selection. Nodes appear in the list.

3. Give the nodal loads a suitable title; e.g “Velocity_of_X Axis_PART2”.

4. Click on IFUN1’s value 0 and a new panel to define the load curve will open. Click on NewCurve_1 and OK to define the data.

5. In the new panel, define the velocity function. The x-axis is time and y-axis is velocity. Assume the

velocity starts at zero and increases to 10mm/ms at 5 ms, then it decreases into ZERO at 10 ms.

6. Repeat previous step to assign a zero velocity value to IFUN2 and IFUN3

7. Velocity Curve Scaling: The velocity peak is 10 mm/ms and we would like this to be 3 mm/ms in X axis. A convenient way is to set the velocity scale factor SCALF =0.3.

8. Make sure the load curve (IFUN1=1) is assigned to this set of nodes. Finish with Apply and Close.

Assigning Material and Part data

This is done using two entities which are linked together; namely:

1. Material data for material data such as modulus, density and plasticity information.

2. Part data for (geometric data such as thickness).

Shell Material data

Select Crash > Materials Editor and then select the type of Material Model; in this case use a 101 –ELASTIC_SHELL. Enter data as in picture hereafter. Save with Apply and Close.

Part data

1. In the explorer panel open the parts folder

2. double click the required part define thickness and material data as indicated on the picture.

3. Finish with Apply and Close.

Tied Material data

Choose Type 301 for Tied material, then assign this material to the Tied through Part Card. Please use parameters as in the figure hereafter

Set the PAM-CRASH Control Data

This controls the analysis and allows specific data like the problem analysis time (in ms in this case), specific output information and output intervals for the results to be defined.

Title

1. In the explorer panel, go to Explorer > Pam Controls > Title

2. Open the title panel in edit mode. A title can now be added. It will appear in Visual Viewer results.

3. Finish with Apply and Close.

Similar steps are done for RUNEND (open, edit and enter 10.0 for the solution time).

For the ouput control (OCTRL)

• Set THPOUTPUT to INTERVAL with 0.1 ms (100 states) for time histories (.THP file)

• Set DSYOUTPUT to INTERVAL with 0.5 ms (20 states) for deformed structure (.DSY file)

• Click Apply and Close.

Special output options

By default only limited node and element time history information is stored on the .THP and .DSY files; for example, nodal displacements and velocities, and element local stresses. A wide range of additional information is available, but this must be specified. For example in the explore option Controls > PamControls > OCTRL click on the tab Advanced. Then click on SHLTHP > ALL > OK and click on SHLPLOT> ALL > OK to output all available shell contour variable to the .DSY and .THP files. Finish with Apply.

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Click on File > Export and save the dataset with a suitable name, e.g. Tied_elastic.pc. Make sure the directory location for the export is correct.

• Remark 1: The File >Save option would save the model as a vdb binary format, readable by Visual Environment but not by the solver.

• Remark 2: Some formats (e.g. DYNA3D and NASTRAN) can also be saved: See the Data type options. However, a different context should be loaded to define conditions for these solvers.

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Start the simulation

Open the PAM-SYSTEM folder on the Desktop. The dataset file name and its location will be requested.

If the dataset is valid, it will proceed through the dataset initialization phase into the solution phase. If there are data errors the run will stop with an abnormal termination message. Inspect the output file for errors (search for ‘ERROR’ and investigate). Correct the dataset; preferably in VISUAL CRASH (or in the editor) and run the analysis again.

The solver progression can be monitored by the information displayed in the listing windows: CYCLE TIME TIME-STEP ELEMENT NO DTMIN FAC. KINETIC EN INTERNAL EN TOTAL EN DTMIN NB. 6190 0.9512E+01 0.1483E-02 SHELL 119 0.1000E+01 0.2104E+00 0.7129E+03 0.8667E-01 0

Once the message NORMAL TERMINATION appears in the listing windows, you can proceed to Part 4, results evaluation:

N O R M A L T E R M I N A T I O N TOTAL NUMBER OF CYCLES = 6519 AVERAGE TIME PER ZONE CYCLE = 0.5113E+01 NUMBER OF SHELLS ELIMINATED = 0 NUMBER OF SOLIDS ELIMINATED = 0 NUMBER OF BEAMS ELIMINATED = 0 GLOBAL CONTACT SEARCHES = 10 CPU(s) ELAPSED(s) CPU% ELAPS% -------------------------------------- INPUT/INITIALIZATION 1.0000E+00 1.9000E+01 25.00 76.00 INTERNAL FORCES 1.0000E+00 1.0000E+00 25.00 4.00 NODAL OPERATIONS 2.0000E+00 3.0000E+00 50.00 12.00 OUTPUTS 0.0000E+00 1.0000E+00 0.00 4.00 CONTACTS 0.0000E+00 1.0000E+00 0.00 4.00 CONSTRAINTS(RB,RW,BC..) 0.0000E+00 0.0000E+00 0.00 0.00 KJOINT/MBS SOLVERS 0.0000E+00 0.0000E+00 0.00 0.00 ADAPTIVE MESH (STAMP) 0.0000E+00 0.0000E+00 0.00 0.00 -------------------------------------- TOTALS 4.0000E+00 2.5000E+01 100.00 100.00 -------------------------------------- CPU TIME 4.000E+00 (s) ELAPSED TIME 2.500E+01 (s) RATIO CPU/ELAPSED TIME 16.00 % NORMAL TERMINATION,EXITO MESSAGE

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Starting Visual Viewer

Activate the Visual-Viewer PAM context.

Two files are available for results visualization:

• filename.THP stores time history information at selected points, elements, etc.

• filename.DSY contains deformation and contour plots of the full structure.

Basic 3D Model Display (.DSY file)

Open both results files at once using File > Open Project. The geometry of the model is displayed.

Click the last arrow of the animation toolbar to display the last state.

Click “Show All” on the toolbar to display all parts, including the link.

Time history results (.THP file)

Go to File > Import & Plot to open the curve plotting panel. Make sure the THP file is selected.

1. Select entity type GLOBAL

2. Select kinetic, internal and total energies under “components”

3. Select multiple curves per graph

4. Click PLOT.

The total energy remains constant: the run is stable.

Using similar steps, time history information can be plotted for:

• stress-strain variables for elements to be selected in VCP (output > Nodal Time History)

• Node kinematics for the nodes selected in VCP (output > Nodal Time History)

• Forces in the tied interface forces (select SECTION entity type)

Animation

Go to Results > Animation Control

Press Play and use the Speed Control slider to adjust the viewing speed.

Additional tabs are available for overlaying the Initial Mesh or viewing selected states simultaneously. Click Close to exit this panel.

The tied interface appears as one-dimensional elements connecting master and slave parts.

◊ The tied elements are overly stretched.

Contour of stresses

Click Results > Contour and under Entity types activate entity type SHELL can be selected and, for example, the variable Max equivalent Stress over thickness.

◊ The stresses are largely over the steel yield stress (~0.3 GPa for mild steel). For such stretching, we should use an elastic-plastic material model.

The model is purely elastic, and the validity limits for this type model have been exceeded.

Some shell elements of part 1 and part 2 have non-physical deformations They are actually zero-energy modes that occur in under-integrated element formulations. They are called hourglass modes due to the shape of the elements.

We will next overcome these two problems by using an elastic-plastic material model for parts 1 and 2.

Save the session as Template

You can save the current Visual-Viewer session as a template, e.g. “Tied.tpl”. The template will be used at next iteration to rebuild automatically all result pages.

Then, just go to File / New Session and select again the Visual Crash for PAM context.

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Model Modification

Open again the filenename.pc file.

1. Change part 1 and part 2 material type from 101 to 103.

2. Open the material editor and create a new material (you may also modify the existing material).

3. Choose the material type 103 (iterative plasticity)

4. Assign a new name to this material, for example you can call it “Material_Elastic_Plastic”(highlighted in the purple color)

5. Input parameters as in the following screen shot (highlighted in the red and brown color)

•

6. Click on Apply and Close buttons

7. If you created a new material, assign it to part 1 and part 2 by editing Part data

Export the Model and run

As in former steps, export the model with a new name, “Tied_Elastic_Plastic.pc”, and run the new model using the solver.

Results update using the template

1. Open the Visual Viewer context and go to File > Open.

2. In the Open dialog, choose to open file as “template file”

3. Select the template you saved in the previous Visual Viewer session, Tied.tpl.

4. Choose the new DSY and THP files to be read

5. Press OK ◊ The results from last session are rebuilt using the new files

6. The results of the previous session are then displayed again

7. Select page 1 in the explorer.

8. Go to Spectrum control and perform a reset to adjust the color scale to the new results.

Key results

• The new stresses have normal values, and no hourglass deformation is observed.

• The plates plastify and limit the effort in the link to about 52 kN. (Click on the force curve to display min/max information in the console).

Possible extension

The maximum force in the link is 52 kN (. For an area of 20 x 60 = 1200 mm2, this gives an approximate stress of 43 MPa. The adhesive may not sustain such a high stress. The exercise can be extended by the introduction of a rupture model (RUPMO in VCP auxiliary folder).