Assignment 5-RADIOSS Interfaces & Study of Effect of Notches Challenge

Aim: To Create the mesh for bumper assembly, the mesh size should be 6mm. Simulate the given model with seven cases in radioss per the problem statement and compare it using various plots.

Objective:

There are 2 different types of cases to be followed

Model 1:

Create a Mesh in Bumper Assembly, with a mesh size of 6mm. 

Model 2:

1. Run the crash tube model as it is.
2. Change the Inacti=6 and run.
3. Create the type 11 contact and run.
4. Remove both notches and remove the boundary condition on the rigid body node then run.
5. Create a new notch in the middle, select the whole section, and run.
6. Create a new notch with nodes only from opposing 2 faces and run.

Model 1:

Model 1:- Meshing of the bumper assembly 

Import the model in Hypermesh.

To open the ".HM" files, Menu Bar -> Open -> Select the Model -> Click Open -> Click.

Step 2:

Set the Quality Criteria for Mesh as 6mm in the Element Size box and select the surface for the meshes.

Below, the picture is shown as a meshed component

Giving proper connections:-

Now we have created a connection between the crash box and the rear bumper. So go to connectors - seam and provide the necessary values.

The green and Red lines are Seam Connectors for engaging the model.

We have to connect the crash box and rear bumper, to give accurate results when we perform the analysis. There are different types of connections available, apart from this we have chosen seam weld which is used to connect the two different materials. The below diagram shows the seam connection between the crash box and the rear bumper.

Model 2: 

Case 1:

Run the crash tube model as it is.

To create the THPART we have to click on the output Blocks and create the THPART, in entity id instead of nodes keep components and select all four components and click on ok. Then the TH part is created.

Property:

The major advantage of the Type7 interface is that it is non-oriented and slave nodes can belong to the master surface enabling self-impact. The following are the defined parameters in the model -

1. Istiff = 4 (affects how the stiffness is calculated)
2. Igap = 0 (determines how the size of the gap is calculated)
3. Gapmin = 1 (min. gap for activation of interface)
4. Iform = 2 (stiffness-based formulation for sliding forces)
5. Iacti = 0 (action to take if initial penetration exists)
6. Stmin = 1 (min thickness in the contact to avoid too soft contact)

    Istiff = 4 will set the stiffness of the interface based on the softer of the master and slave.

    Igap = 0 will take the size of the gap defined by Gapmin.

    Iacti = 0 will take no action against initial penetrations, if any.

    To run the simulation, go to Analysis > Radioss. Using the save option, give the destination to where the file is to be saved. Toggle the export options to all and run options to analyze.

To simulate the model, Go to the Analysis tab, Select the Radioss option -> Select the location to save the file -> Check the include collectors box -> In the options tab, type “-nt 4” -> Click Radioss.

Below it shows that the Simulation is run completely without any error.

Open the output file and check the energy error and mass error as shown in the image below.

From the output file energy error is -3.8%% and the mass error is 0% which is less than -15% to 2% and 1% respectively, so we can accept the results and plot the graphs by using hypergraphs.

Displacement Plots:

2.8e+2 MM and Min of 0 MM

Von-Mises Stress:

Max of 6.949e-1 N/mm^2 and Min of 0 N/mm^2

Plastic Strain:

Max of 1.18 mm/mm and Min of 0 mm/mm

Open hypergraph 2D for observing the energy plot data from the TA01 file, then the below results have been attached. 

 As seen in the graph, the kinetic energy is maximum at the beginning which starts decreasing once the crush tube impacts the rigid wall.

This energy is converted into strain energy as the crush tube deforms as observed by the increase in internal energy of the system.

Energy error is about -3.8% which is acceptable. A part of the total energy is used by the contact energy as seen in the graph.

As total energy reduces, contact energy increases. Contact energy = contact force*distance moved to avoid penetration. The contact force is the energy spent by enabling a contact force to avoid penetration.

This should be a minimum. As seen above, the contact energy is very less for most of the time and there is a slight increase in the contact energy at the end of the simulation.

For rigid walls, there is a sudden rise in the peak value of rigid wall force after T=30. By this time, the crush tube is completely crushed and therefore the deformed model having no further scope for deformation gets pushed against the wall with some velocity to which the rigid wall reacts.

Case 2:

Change the Inacti=6 and run

In this case, the model is imported, and simulated with recommended properties whereas we have to change Inacti = 6 as per the problem statement. The Type 7 contact interface is used with recommended properties as shown in the Figure.

The below picture is shown to the simulation is done successfully. 

After changing the parameters simulate with the same steps to be carried out as per the previous case. The simulation is shown in GIF below. Plot the graphs of energies the same as in the above case.

Energies Error of -3.8 % and Mass Error of 0 is been occurred in this results.

 

Displacement Plots:

Max of 2.8 mm and Min of 0 mm

Von-Mises Stress:

Max of 4.69e-1 N/mm^2 and Min of 2.23e-2 mm

Plastic Strain:

Max of 4.15e-1 mm/mm and Min of 0 mm/mm

 The nature of the deformation and the energy graph is similar compared to case 1. Energy error is -3.8% which is acceptable. 

Case 3:

In this case, we have to create a Type11 contact and run the simulation. To create the contact, we will use Hypercrash, which is a specialized preprocessor for Radioss.

After importing the file, go to Loadcase > Contact interface. Click on Create icon and select Edge to Edge (Type11). Type11 interface is defined by identifying master and slave lines.

This contact, when added with Type 7 can help to capture the physics correctly. This is very helpful in case of edges crossing where the nodes of the element are far away and the element is near another

     surface.

The simulation is run properly, with no errors.

Here the Energy drops to -0.2%, with slight major changes in energy.

 

Displacement Plots:

Max of 3.04e+2 mm and Min of 0 mm.

Von-Mises Stress:

Max Stress of 6.451e-1 N/mm^2 and Min Stress of 0 N/mm^2

Plastic Strain:

Max Strain of 4.32e-1 mm/mm and Min Strain of 0 mm/mm

Here the deformation is different, as compared to the above 2 cases, with the pick of 18KN of resultant forces and There is not much difference, here there is slight hike and downs in at the ranges of 27sec in both Contact forces and Kinetic Forces.

Case 4:

  Here, we have to remove both the notches and the boundary conditions on the rigid body and run the simulation. To remove the notches,

we can use align option from the node edit option available under, the Geom page. Go to Geom > node edit > align. In the 1st and 2nd end selector, select two nodes (black) respectively, which will define a line along which the selected nodes on the notch (white) will be placed, thus removing the notch. Click on align. The nodes will be aligned as seen below. Repeat the same procedure for the entire notch.

Before Updating:

After Updating:

To remove the boundary conditions on the rigid body, go to Solver > BCS > BCS > rbody_12456. Uncheck DOF1, DOF2, DOF3, DOF4, DOF5, and DOF6 which will allow translation in X, Y, Z, and rotation in X, Y, and Z directions respectively.

As seen here, there are no notches on the crush tube. During impact, there is no localized deformation as there are no notches present and the deformation progresses as expected.

The nature of the energy graph is also similar to the previous case. Energy error is about -2.4% which is acceptable. 

Displacement Plots:

Max Displacement of 3.049e+2 mm, and Min Displacement of 0 mm.

Von-Mises Stress:

Max Stress of 5.422e-1 N/mm^2 and Min Stress of 7.702e-3 N/mm^2

Plastic Strain:

Max Strain of 8.85e-1 mm/mm and 0 mm/mm

The energies results are almost similar to the previous case, with a Sudden increase at 27sec in the contact and Kinetic energies 

Case 5:

In this case, we have to create a new notch in the center and run the simulation. We can create a notch by using the translate option available under the Tool page. To properly create the notch,

use the N1, N2, and N3 options to define the plane of translation. Translate the nodes by 4mm and create the notch.

Updated Mesh with New Notches:

This solver shows that the results are been run smoothly with no errors.

Here the no.of cycles runner is lesser than in the previous cases. with drops -of 3.4% in negligible amounts.

Displacement Plots:

Max Stress of 2.79e+2 mm and Min Stress of 0 mm

Also here, after impact, deformation is first observed in the middle in the portion where the notch is.

Von-Mises Stress:

Max Stress of 4.49e-1 N/mm^2 and Min Stress of 1.43e-2 N/mm^2 

Plastic Strain:

Max Strain of 9.89e-1 mm/mm and Min Strain of 0 mm/mm

 The nature of the deformation and the energy graph are similar compared to previous cases. Energy error is about -2.3% which is acceptable.

Case 6:

Create notches on two opposing surfaces at mid-portion and run the simulation. The procedure to create a notch is the same as discussed earlier using the Translate tool.

 

 

Energy errors of -2.8% is been occurred in these cases

Displacement Plots:

Max Displacement Plots of 2.8e+2 mm and Min Displacement Plots of 0 mm.

Von-Mises Stress:

Max Stress of 5.424e-1 N/mm^2 and Min Stress of 5.522e-3 N/mm^2 

Plastic Strain:

Min Strain of 5.808e-1 mm/mm and Min Strain of 0 mm/mm

Deformation is first observed in the notched region and the energy graph is similar compared to previous cases. Energy error is about -2.8% which is acceptable. 

Outcomes:

Conclusion:

• The Bumper model has been meshed and welded (seam) with an element size of 6mm and is ready for further solving and post-processing.
• All 6 cases of crash tubes have been simulated and results are compared using various energies plots.