The table below lists the DYNA *DEFORMABLE_TO_RIGID keywords.
DYNA keyword Purpose
*DEFORMABLE_TO_RIGID Switch parts to rigid at the start of the calculation
*DEFORMABLE_TO_RIGID_A UTOMATIC
Switch parts to rigid or to deformable at some state in the calculation
*DEFORMABLE_TO_RIGID_IN ERTIA
Define inertial properties for the new rigid bodies created when the deformable parts are switched
Below is the card format for specifying parts for these keywords:
1 2 3 4 5 6 7 8
PID MRB
PID is the ID of the slave part to be switched
MRB is the part ID of the master rigid body to which the part is merged. This field exists only for *DEFORMABLE_TO_RIGID and for
*DEFORMABLE_TO_RIGID_AUTOMATIC when the part is to be switched to rigid.
In HyperMesh, rather than specify one part at a time, you specify an entity set containing all of the desired slave parts. On export, the entity set’s part IDs are written to the DYNA input file according to the above card format.
Exercise 1: Define Model Data for the Seat Impact Analysis.
This exercise will help you continue to become familiar with defining LS-DYNA model data using HyperMesh.
This exercise is comprised of defining and reviewing model data for an LS-DYNA analysis of a vehicle seat impacting a rigid block. The seat and block model is shown in the image below.
Seat and block model
Step 1: Load the LS-DYNA user profile.
Step 2: Retrieve the HyperMesh file seat_start.hm.
Step 3: Create an xy plot.
1. Access the plot panel one of the following ways:
• From the Setup menu, point to XY plots, click Create Plots.
• From the Post page, click xy plots and select plots panel.
2. For name = type seat_mat.
3. Verify the plot type is set to standard.
4. Leave the like field empty.
When an existing plot is selected, the new plot adopts its attributes.
5. Create plot.
6. Return to the xy plots module menu..
Step 4: Input data from a file to create two stress-strain curves.
1. Access the read curves panel one of the following ways:
• From the Setup menu, point to XY plots, click Read Curves.
• From the Post page, click xy plots and select read curves panel.
2. For plot =, leave it set to seat_mat.
3. Browse for the file named seat_mat_data.txt.
4. Input the file.
Notice two curves are created and are named 0.001 strain rate for steel (curve1) and 0.004 strain rate for steel (curve2).
5. Return to the xy plots module menu.
Step 5: Create a dummy xy curve to be used to create *DEFINE_TABLE.
1. Access the edit curves panel one of the following ways:
• From the Setup menu, point to XY plots, click Edit Curves.
• From the Post page, click xy plots and select edit curves panel.
2. Go to the create sub-panel.
3. For plot = select seat_mat.
4. Activate the math option.
5. In the x= field enter {0.0, 0.2}.
6. In the y= field enter {0.4, 0.4}.
7. Create the curve.
Notice the curve is displayed in the seat_mat plot and has the name curve3.
8. Return to the main menu.
Step 6: Create *DEFINE_TABLE from the dummy curve.
1. Access the card editor panel in one of the following ways:
• From the Setup menu, click Card Editor
• From the toolbar, click the card editor icon 2. Set the entity selector to curves.
3. Select curve3.
4. Edit the curve.
7. For the strain rate VALUE(1) specify 0.001.
8. For the strain rate VALUE(2) specify 0.004.
9. For CurveId(1) select curve1.
10. For CurveId(2) select curve2.
11. Return to the main menu.
Step 7: Create the non-linear material.
(*MAT_PIECEWISE_LINEAR_PLASTICITY)
1. Do one of the following to create any LS-Dyna keyword card:
• From the Tools menu, click Create Cards
• Right -click anywhere in Solver Browser window and click Create a new card 2. From the Ls -Dyna keyword list, point to *MAT.
3. Select *MAT_PIECEWISE_LINEAR_PLASTICITY.
4. For name = type steel and click OK.
Notice *MAT_PIECEWISE_LINEAR_PLASTICITY card is created.
5. For density [Rho] specify 7.8 E-6.
6. For Young’s Modulus [E] specify 200.
7. For Poisson’s ratio [NU] specify 0.3.
8. For yield stress [SIGY] specify 0.25.
9. For the *DEFINE_TABLE id [LCSS] specify the curve3 (id=5).
10. Return to the collectors panel.
11. Return to the main menu.
Step 8: Update the base_frame and back_frame components with the new non-linear material.
1. Click on Content Table found under DYNA Tools in the Utility Menu.
2. From the Table menu, click Editable.
3. Select the components base_frame and back_frame.
4. For Assign Values:, select Material name 5. For HM -Mats:, select steel
6. Click Set.
7. Click Yes to confirm.
8. Close the Content Table window.
Steps 9-12: Create a beam element, *ELEMENT_BEAM, to complete the seat’s back_frame connection to the side_frame on the left side.
Step 9: Restore a pre-defined view for ease of following the next steps.
1. From the View menu, click User Views.
A window pops up.
2. Click restore1 to see the beam view.
Step 10: Set the current component to beams.
1. From the Preferences menu, click Global Parameters.
2. For component =, select the beams component.
This component has a pre-defined section, *SECTION_BEAM, with a tubular cross section associated to it.
3. Return to the main menu.
Step 11: Select the BEAM type for the HyperMesh beam configuration.
1. Access the Element Types panel in one of the following ways:
• From the Mesh menu, click Element Types.
• From the 1D page, click elem types.
2. For beam = select BEAM.
3. Return to the main menu.
Step 12: Create the beam.
1. From the 1D page, go to the beams panel.
2. Go to the bar2 sub-panel.
3. Click the leftmost switch and select node.
A direction node is selected later to define the beam’s section orientation.
4. Click the Node A selector to make it active.
5. Select the center node of the left nodal rigid body for Node A.
Node B is active now.
6. Select the center node of the right nodal rigid body for Node B.
7. Select any non-center node of one of the nodal rigid bodies for the direction node.
Notice the beam is created.
Step 13: Restore a pre-defined view and display node IDs for ease of following the next steps.
1. From the View menu, select User Views.
2. Click restore2 to see the nodal rigid body view.
3. On the Tool page, go to the numbers panel.
4. Leave the entity selector set to nodes.
5. Click nodes and select by id. Enter 425-427, 431 and press ENTER.
6. Display on the IDs.
7. Return to the main menu.
Step 14: Set the current component to welding.
1. From the Preferences menu, click Global Parameters 2. For component =, select the welding component.
3. Return to the main menu.
Step 15: Select the RgdBody type for the HyperMesh rigid configuration.
1. Enter the Mesh menu, click Element Types.
2. For rigid = select RgdBody.
3. Return to the main menu.
Step 16: Create the nodal rigid body (*CONSTRAINED_NODAL_RIGID_BODY).
1. From the Tools menu, click Create Cards.
2. From the Ls -Dyna keyword list, point to *CONSTRAINED 3. Click on *CONSTRAINED_NODAL_RIGID_BODY 4. Set nodes 2-n to multiple nodes.
5. Select the beam’s free end for node1.
6. Select nodes 425, 426, 427 and 431 for nodes 2-n.
7. Leave active the attach nodes as set option.
8. Create the nodal rigid body.
9. Return to the main menu.
A *CONSTRAINED_JOINT_STIFFNESS is not created; it is not needed for this joint to work.
Step 17: Restore a pre-defined view and display node IDs for ease of following the next steps.
1. From the View menu, click User Views.
2. Click restore3 to see the joint view.
3. From the Tool page, go to the numbers panel to display node IDs.
4. Leave the entity selector set to nodes.
5. Click nodes and select by id. Type 1635, 1636 and press ENTER.
6. Turn on the ids.
7. Return to the main menu.
8. From the toolbar, click the Wireframe Elements (Skin Only) icon to change to standard graphics mode.
Step 18: Activate coincident picking.
1. Press O on the keyboard to access the options panel.
2. Go to the graphics sub-panel.
3. Activate coincident picking.
4. Return to the main menu.
Step 19: Set the current component to joint.
1. From the Preferences menu, click Global Parameters.
2. For component = select the joint component.
3. Return to the main menu.
Step 20: Create a revolute joint between two nodal rigid bodies (*CONSTRAINED_JOINT_REVOLUTE).
The rigid bodies must share a common edge along which to define the joint. This edge, however, must not have the nodes merged together. The two rigid bodies will rotate relative to each other along the axis defined by the common edge.
1. From the Tools menu, click Create Cards.
2. From the Ls -Dyna keyword list, point to *CONSTRAINED 3. Click on *CONSTRAINED_JOINT_REVOLUTE \ 4. Set the joint type to revolute.
6. Move the mouse to node 1635 in the coincident picking display and click on it to select it for node 1 in rigid body A.
Node2 is now active.
7. Click on node 1635 again to see the coincident picking mechanism and select node 1633 for node 2 in rigid body B.
Node3 is now active.
8. Click on node 1636.
Two coincident nodes are displayed – 1636 and 1634 9. Select node 1636 for node 3 in rigid body A.
Node4 is now active.
10. Select node 1634 for node 4 in rigid body B.
11. Create the joint.
12. Return to the main menu.
Steps 21-23: Define *DEFORMABLE_TO_RIGID to set up the moving seat as rigid until the time of impact with the block, to reduce computation time.
Step 21 Create an entity set that contains the components base_frame, back_frame, and cover.
1. From the Setup menu, click Entity Sets.
2. For name = type set_part_seat.
3. For card image, select Part
Notice the entity selector is set to comps.
4. Select the base_frame, back_frame and cover components.
5. Create the set.
6. Return to the main menu.
Step 22: Define *DEFORMABLE_TO_RIGID to switch the deformable seat to rigid at the beginning of the analysis.
1. From the Tools menu, click Create Cards.
2. From the Ls -Dyna keyword list, point to *DEFORMABLE_TO_RIGID.
3. Click on *DEFORMABLE_TO_RIGID.
4. For name =, type dtor.
5. For the part set ID, [PSID], specify the set_part_seat set ID.
6. For the master rigid body, [MRB], specify the back_frame component.
7. Return to the main menu.
Step 23: Create *DEFORMABLE_TO_RIGID_AUTOMATIC to switch the rigid seat to deformable when contact between the seat and block is detected.
1. From the Tools menu, click Create Cards.
2. From the Ls-Dyna keyword list, point to *DEFORMABLE_TO_RIGID.
3. Click on *DEFORMABLE_TO_RIGID_AUTOMATIC.
4. For name =, type dtor_automatic.
5. For the unique set number for this automatic switch set, [SWSET], enter 1.
6. For the activation switch code [CODE] select 0.
The switch will take place at [TIME1].
7. For [TIME1] enter 175.
The switch will not take place before this time.
8. Activate R2D_Flag in the menu area.
On export, the number of rigid parts to be switched to deformable is written to the R2D field (card 2, field 6). This number is based on the number of parts in the entity set you select next.
9. Move the scroll bar on the left side of the card image down to see [PSIDR2D].
10. For the [PSIDR2D] field specify the set_part_seat set ID.
11. Return to the main menu.
Steps 24-28: Review the model’s data using the Content Table tool.
• From the Utility menu, click DYNA Tools, then click Content Table.
Step 24: Display only parts with a particular material (Ex: steel).
1. From the Display menu, click By Material.
2. Select material steel and click proceed.
Notice that the GUI and the content table show only those components with material steel assigned. All other components get turned off.
3. Follow the above steps to select components using By Properties and BY thickness option.
Step 25: Display all components.
1. From the Display menu, click By Material.
Notice now that the GUI and the Content Table show all components of the model.
Step 26: Rename a part.
1. From the Table menu, click Editable to make the content table editable. (All columns with a white background can be edited. Ex: Part name, Part id, Thickness etc.)
2. Click on any part name field to edit it.
3. Click Yes to confirm.
4. Click the disp icon to go to the Display panel to notice the part’s new name.
Step 27: Renumber a part id.
1. Click on the Part Id field.
2. Type a number that does not conflict with the existing part IDs.
3. Click Yes to confirm.
Step 28 (Optional): The exercise is complete. Save your work to a HyperMesh file.
Section 2: Define Boundary Conditions and Loads
Exercise 2: Define Boundary Conditions and Loads for the Seat Impact Analysis .
This exercise will help you continue to become familiar with defining LS-DYNA boundary conditions and loads using HyperMesh.
In this exercise, you will define boundary conditions and load data for an LS-DYNA analysis of a vehicle seat impacting a rigid block. The seat and block model is shown in the image below.
Seat and block model
This exercise contains the following three tasks.
• Define gravity acting in the negative z-direction with *LOAD_BODY_Z
• Define the seat’s acceleration with *BOUNDARY_PRESCRIBED_MOTION_NODE
• Export the model to an LS -DYNA 970 formatted input file and submit it to LS-DYNA
Step 1: Make sure the LS-DYNA user profile is still loaded.
Step 2: Retrieve the HyperMesh file seat_2.hm.
Step 3: Define gravity acting in the negative z-direction with *LOAD_BODY_Z.
1. From the Tools menu, click Create Cards.
2. From the Ls -Dyna keyword list, point to *LOAD.
3. Click on *LOAD_BODY_Z.
4. For name =, type gravity.
5. For the load curve LCID, specify the ID of the curve named gravity curve.
6. For the load curve scale factor [SF], specify 0.001.
7. Return to the main menu.