Crash Tube Analysis using Radioss

OBJECTIVE:

To create a mesh for the given bumper assembly with a mesh size of 6mm.

To compare the results obtained after simulation for the cases given below:

1. To run the crash tube model as it is

2. To change the Inacti to 6 and run

3. To create the TYPE 11 contact and run

4. Remove both notches and remove boundary condition on rigid body node and run

5. Create a new notch in the middle, select the whole section and run

6. Create a new notch with node only from opposing 2 faces and run 

PROCEDURE:

For creating a mesh in the given model with a mesh size of 6mm

1. Import the model Bumper System using Hypermesh.

2. Select Geometric Color Mode "By Topo" view to check if there is any geometrical error present in the geometry. If errors are observed, then suitable cleanup must be done before meshing.

3. Go to 2D>>automesh>>element size: 6mm>>mesh type: mixed>>by surfs>>select surfs>>mesh. After meshing match the number of nodes the edges to get a perfect quad type mesh.

4. Go to 2D>>connectors>>spots>>location: nodes>>Select the nodes for which spot weld needs to be given>>give suitable tolerance and diameter of spot>>create.

5. The final meshed model is shown in the figure below.

      

The below procedure is common for all the cases and changes are to be done as per the case

1. Import the file Crush_tube_0000.rad using the radioss solver.

2. Check the material failure property card and changes are done as given in every case

3. Then go to Analysis>>Save the file name as given in the question>>Select number of cores as -nt 4>>Radioss

4. Go to Hyperview>>Load the necessary .h3d file to view the necessary simulation.

5. Get the necessary contours as given in the Hyperview window and save the simulation results contours.

6. Go to Hypergraph>>Load the necessary T01 file to get the various graphs associated with the simulation.

7. Step 1-6 is repeated for various condition changes.

CASE SETUP AND EXECUTION:

Case 1: Run the model as it is

The von-mises contour obtained is shown below:

 

The various energy plots obtained are shown in the figures below:

Case 2: Change Inacti=6 and run

                                       

The von-mises contour obtained is shown below:

The various energy plots obtained are shown in the figures below:

Case 3: Create the TYPE11 contact and run

                                      

The von-mises contour obtained is shown below:

The various energy plots obtained are shown in the figures below:

Case 4: Remove both notches and remove boundary condition on rigid body node and run

The model after removing the notches is shown in the figure below. The notches are removed using align nodes command.

                                      

The boundary condition is removed by deleting the BCS card as shown in the figure below:

                             

The von-mises contour obtained is shown below:

The various energy plots obtained are shown in the figures below:

Case 5: Create a new notch in the middle, select the whole section and run

The notch is created using offset command in Hypermesh.

           

The von-mises contour obtained is shown below:

The various energy plots obtained are shown in the figures below:

Case 6: Create a new notch with node only from opposing 2 faces and run 

                                                     

The von-mises contour obtained is shown below:

The various energy plots obtained are shown in the figures below:

RESULTS AND DISCUSSION:

Case 1: The following results are obtained

From the internal energy vs time plot it can be deduced that, the internal energy increases linearly upto a certain time (between 20ms to 22 ms) and over which it increases rapidly due to the impact of the tube against the wall. The kinetic energy gradually drops over time and between 25 ms to 30 ms there is a slight increase in kinetic energy as observed in the plot. The maximum internal energy is obtained at 26.8 ms. 

From the hourglass energy vs time plot it can be deduced that hourglass energy remains zero throughout due to QEPH element formulation. The contact energy slowly increases and reaches a peak during the time of impact after 26 ms after which it remains constant.

The resultant normal force increases and attains a peak at the time of impact and after which it reduces drastically whereas the resultant tangential forces remain zero. The total resultant force attains a maximum value at 26.6 ms.

The maximum Von-Mises stress obtained is 0.6964 Joules. The maximum contact force obtained is 93.45 kN.

Case 2: The following results are obtained

From the internal energy vs time plot it can be deduced that, the internal energy increases linearly upto a certain time (between 20ms to 22 ms) and over which it increases rapidly due to the impact of the tube against the wall. The kinetic energy gradually drops over time and between 25 ms to 30 ms there is a slight increase in kinetic energy as observed in the plot. The maximum internal energy is obtained at 26.8 ms. 

From the hourglass energy vs time plot it can be deduced that hourglass energy remains zero throughout due to QEPH element formulation. The contact energy slowly increases and reaches a peak during the time of impact after 26 ms after which it remains constant.

The resultant normal force increases and attains a peak at the time of impact and after which it reduces drastically whereas the resultant tangential forces remain zero. The total resultant force attains a maximum value at 26.6 ms.

The maximum Von-Mises stress obtained is 0.6964 Joules. The maximum contact force obtained is 93.45 kN.

Comparison between case 1 and case 2:

In Case 1, type 7 contact interface which is node to surface is used. The disadvantage of type 7 contact is that it does not consider the contact of the edges of the slave element with the master surface. But during the start of the simulation exists thus creating an unstability in simulation. In case 1, default Inacti value is assigned as 0, so it considers the default penetration whereas in case 2, the Inacti is defined as 6 which denotes that gap is variable with time but initial gap is adjusted as per the equation given below:

${\mathrm{Gap}}_0=\mathrm{Gap}–P_0–5\%\cdot (\mathrm{Gap}–P_0)$

$Gap0\; =\; New\; adjusted\; initial\; gap$

$Gap\; =\; Initial\; gap$

$P0\; =\; Initial\; Penetration$

$But\; the\; overall\; results\; does\; not\; vary\; much\; when\; case\; 1\; and\; case\; 2\; are\; compared.$

Case 3: The following results are obtained

From the internal energy vs time plot it can be deduced that, the internal energy increases linearly upto a certain time (between 20ms to 22 ms) and over which it increases rapidly due to the impact of the tube against the wall. The kinetic energy gradually drops over time and between 25 ms to 30 ms there is a slight increase in kinetic energy as observed in the plot. 

From the hourglass energy vs time plot it can be deduced that hourglass energy remains zero throughout due to QEPH element formulation. The contact energy slowly increases and reaches a peak during the time of impact at 26.7 ms (2019.5 J) after which it remains constant. 

The resultant normal force increases and attains a peak at the time of impact and after which it reduces drastically whereas the resultant tangential forces remain zero. The total resultant force attains a maximum value around 27 ms.

The maximum Von-Mises stress obtained is 0.6914 Joules. The maximum contact force obtained is 82.62 kN.

Case 4: The following results are obtained

 

From the internal energy vs time plot it can be deduced that, the internal energy increases linearly upto a certain time (between 20ms to 22 ms) and over which it increases rapidly due to the impact of the tube against the wall. The kinetic energy gradually drops over time and between 25 ms to 30 ms there is a slight increase in kinetic energy as observed in the plot.

From the hourglass energy vs time plot it can be deduced that hourglass energy remains zero throughout due to QEPH element formulation. The contact energy slowly increases and reaches a peak during the time of impact at 27.6 ms (1571.2 J) after which it remains constant.

The resultant normal force increases and attains a peak at the time of impact and after which it reduces drastically whereas the resultant tangential forces remain zero. The total resultant force attains a maximum value around 27 ms.

The maximum Von-Mises stress obtained is 0.6506 Joules. The maximum contact force obtained is 57.06 kN.

Comparison between case 3 and case 4:

In case 3, TYPE11 contact is defined for edge to edge contact. It is similar to TYPE7 contact interms of gap definition. In case 4, the boundary conditions are deleted and also all the notches are removed and then simulation is done.

The contact force is reduced to 57.06 kN in case 4 whereas in case 3 it was 82.62 kN. The Von Mises stress is also lower in case 4. This is due to lack of notches in case 4. The contact energy in case 4 obtained is 1571.2 J whereas in case 3 it is 2019.5 J which is higher in the latter due to presence of notches.

Case 5: The following results are obtained

From the internal energy vs time plot it can be deduced that, the internal energy increases linearly upto a certain time (between 20ms to 22 ms) and over which it increases rapidly due to the impact of the tube against the wall. The kinetic energy gradually drops over time and between 25 ms to 30 ms there is a slight increase in kinetic energy as observed in the plot. The maximum internal energy is obtained at 27.1 ms (42033.375 J)

From the hourglass energy vs time plot it can be deduced that hourglass energy remains zero throughout due to QEPH element formulation. The contact energy slowly increases and reaches a peak during the time of impact at 27 ms (2151.28 J) after which it remains constant.

The resultant normal force increases and attains a peak at the time of impact and after which it reduces drastically whereas the resultant tangential forces remain zero. The total resultant force attains a maximum value around 27 ms. (1410.8 units)

The maximum Von-Mises stress obtained is 0.6420 Joules. The maximum contact force obtained is 92.16 kN.

Case 6: The following results are obtained

From the internal energy vs time plot it can be deduced that, the internal energy increases linearly upto a certain time (between 20ms to 22 ms) and over which it increases rapidly due to the impact of the tube against the wall. The kinetic energy gradually drops over time and between 25 ms to 30 ms there is a slight increase in kinetic energy as observed in the plot. The maximum internal energy is obtained at 26.9 ms (42375.625 J)

From the hourglass energy vs time plot it can be deduced that hourglass energy remains zero throughout due to QEPH element formulation. The contact energy slowly increases and reaches a peak during the time of impact at 26.9 ms (1856.646 J) after which it remains constant.

The resultant normal force increases and attains a peak at the time of impact and after which it reduces drastically whereas the resultant tangential forces remain zero. The total resultant force attains a maximum value around 26.8 ms. (1267.59 units)

The maximum Von-Mises stress obtained is 0.6676 Joules. The maximum contact force obtained is 78.00 kN.

Comparison between case 5 and case 6:

In case 5, a new notch is created in the middle and simulation is done whereas in case 6 the notches are created only in the opposite sides and simulation is done.

The contact forces is reduced to 78.00 kN in case 6 whereas in case 5 it was 92.16 kN. The Von Mises stress is also lower in case 5. This is due to uniform deformation across the notches. The contact energy in case 5 obtained is 2151.8 J whereas in case 6 it is 1856.646 J which is higher in the former due to presence of notches. Also, the value of resultant force obtained for case 6 is 1267.59 units which is lower than that of 1410.8 which is obtained in case 5.

The results obtained for energy and mass error is given in the table below:

Simulation Cases	Energy Error	Mass Error	Simulation Time (s)
Case 1	-4.6%	0%	240.16
Case 2	-4.6%	0%	212.91
Case 3	-4.6%	0%	234.78
Case 4	-3.7%	0%	190.87
Case 5	-4.9%	0%	1147.16
Case 6	-4.6%	0%	186.62

CONCLUSION:

The following conclusion can be drawn based on the results obtained in simulation

The selection of contact interface depeneds on the type of application. Suitable contact interface which are defined below has to be selected depending upon the application.

1. Type 7: Node to surface contact

2. Type 11: Edge to edge conact

3. Type 24: Node and surface to surface

4. Type 17: Mixture of Type 7 and Type 11

5. Type 2: Widely used for welding connections.

All the above types of contact interface has to be used with the recommended property values. Depending on the type of application the values may vary.

The presence of notches tend to coarsen the mesh quality. When the notches in the simulation were reduced there was a change in values of von mises energy, contact energy, internal energy and contact forces as discussed in the results. There is a smoother transmission of force obtained in the presence of notches. Thus, notches play a significant role in the crash simulation. 

Drive Link: https://drive.google.com/file/d/1UL0IVzTqCiXWva9oMO6CLIhdh_p9RXEG/view?usp=sharing