RADIOSS Interfaces & Study of Effect of Notches Challenge | HyperMesh

OBJECTIVE :

• To create the mesh for bumper assembly given below with target element size as 6mm.

         

• To apply the six different cases to the Crash Tube model given below.

         

• To plot the Rwall forces, contact forces and internal energies and comment on the resulting plots.
• To compare total number of cycles, energy error, mass error and simulation time of all the cases.
• To notice the analysis animations of different cases and describe them in brief.
• To list down case by case result and conclusion difference caused due to all the different cases.

MODEL :

We have the Bumper Assembly model and we have to mesh it using 2D shell elements. So before meshing, we have to look for geometrical and topological defects in the model. At first we will clear all Temp nodes in the model. We can see some free edges in some components which we will attach to the parent component using extend over edges option in surface edit panel under Geom page.

     

If any geometrical or topological defects exist in the model, we will clean those using commands from quick edit panel. Then we will mesh each component one by one using 2D Automesh panel, by using mixed type of mesh and having target element size as 6 mm. During meshing, we will make sure that there are no trias generated as we want only quads with good mesh flow. Now we will connect the components having gaps between them with connectors. So we will go to connectors panel in 2D page and we will select spot weld connectors to connect the components. Here we will specify the node location where we want the spot weld, select the connecting components and then click on create to create the connectors. After connecting all the components, the model is ready.

RESULT :

      

 

 

CASE SETUP AND EXECUTION :

CASE 1 – Run the Crush Tube model as it is.

Steps to perform for this particular case;

Step I. In Radioss, Import Crush_Tube_0000.rad starter file using Import Solver Deck menu.

Step II. Navigate to Radioss panel in Analysis page.

Step III. Save the model as Case_1_0000.rad in a specific folder path, tick the include connectors option and under options folder write –nt 4 and click on Radioss to run the simulation.

Step IV. Open .out Engine file from specified path and check final value of Energy error and mass error and check the values of Simulation time and Total number of cycles.

 

 

In the above images, red box indicates the Total number of cycles, blue box indicates Energy error, green box indicates Mass error and brown box indicates Simulation time.

Step V. Open new model and switch to HyperView from Hypermesh.      

Step VI. Load .h3d file from specified path, play the animation and plot contour of Von Mises stress using Simple averaging method.

Step VII. Open HyperGraph 2D in a new window, load T01 file and plot the Rwall forces, contact forces and energies required.

Animation and Results –

     

In this model, we can see that the initial bending or failure occurs at the upper notch and then as the simulation progresses, the lower notch bends. Due to this, the lower part of the tube deforms completely and after complete deformation of the lower part, the upper half part deforms and finally the whole tube deforms in zigzag way.

RWALL Forces –

     

From the above plot, we can notice that the effect of normal force at the initial stage is less and as the component deforms, the normal resultant force increases as there is very less amount of opposing resistance in the component when it is deformed. Finally the normal and total resultant force reaches zero when the component is fully deformed.

Contact Energy –

     

Contact energy increases with time as the model deforms in zigzag way, there happens to be material accumulation layer by layer and thus increases contact forces which are higher at the end. After 27^th ms, we can see some decrease in contact energy because after complete deformation, there is some opposing spring reaction force.

Internal, Kinetic and Total Energy –

     

The Kinetic energy which is having higher value at the start of the simulation decreases as the simulation progresses with time and gets converted to internal energy, thus internal energy increases with time. The Total energy in the system is almost constant where the slight decrease is due to the energy error which is caused due to the resistive forces between master segment and slave nodes.

CASE 2 – Change Inacti = 6 and run the model.

Steps to perform for this particular case;

Step I. In Radioss, Import Crush_Tube_0000.rad starter file using Import Solver Deck menu.

Step II. Open INTER > Type 7 under Solver Browser.

Step III. Change the Inacti value to 6.

     

Step IV. Navigate to Radioss panel in Analysis page.

Step V. Save the model as Case_2_0000.rad in a specific folder path, tick the include connectors option and under options folder write –nt 4 and click on Radioss to run the simulation.

Step VI. Open .out Engine file from specified path and check final value of Energy error and mass error and check the values of Simulation time and Total number of cycles in the same way as mentioned in the previous case.

The values of Energy error, Mass Error, Simulation time and Total number of cycles are mentioned in tabulated format for all cases in Results.

Step VII. Open new model and switch to HyperView from Hypermesh. Load .h3d file from specified path, play the animation and plot contour of Von Mises stress using Simple averaging method.

Step VIII. Open HyperGraph 2D in a new window, load T01 file and plot the energies required.

Animation and Results –

     

The above animation is almost similar to the Case 1 as any geometrical changes are not done in the model.

RWALL Forces –

     

The Rigid wall forces are same as discussed in the previous case.

Contact Energy –

     

The contact energy is the same as discussed in the previous case.

Internal, Kinetic and Total Energy –

     

The internal energy, kinetic energy and the total energy are the same as discussed in the previous case.

CASE 3 – Create the new type 11 contact and run the model.

For this case, we will use HyperCrash to create new interface type easily. HyperCrash is a specialized preprocessor for Radioss.

Step I. In HyperCrash, Import Crush_Tube_0000.rad starter file using Import from File menu or Click and drag the Crush_Tube_0000.rad file from its location.

Step II. In menu bar, navigate to LoadCase > Contact Interface.

Step III. Under Contact Interface panel, right click and create new Edge to Edge (Type 11) contact and configure the recommended parameters as shown below.

     

As the model is self-impacting, we will check Self Impact option which implies that the components selected for Master will also get selected as Slave because the edge to edge contact happens when impacting line can belong to the master and the slave side. So for Master line option, we will select all the 4 components of the model.

Step IV. Export and save the edited Crush Tube file to Radioss to a specified path from File menu.

Step V. Open Radioss and Import the saved Crush_Tube_0000.rad starter file using Import Solver Deck menu.

Step VI. Navigate to Radioss panel in Analysis page.

Step VII. Save the model as Case_3_0000.rad in a specific folder path, tick the include connectors option and under options folder write –nt 4 and click on Radioss to run the simulation.

Step VIII. Open .out Engine file from specified path and check final value of Energy error and mass error and check the values of Simulation time and Total number of cycles in the same way as mentioned in the previous cases.

Step IX. Open new model and switch to HyperView from Hypermesh. Load .h3d file from specified path, play the animation and plot contour of Von Mises stress using Simple averaging method.

Step X. Open HyperGraph 2D in a new window, load T01 file and plot the energies required.

Animation and Results –

     

The above animation is almost similar to the previous cases as any geometrical changes are not done in the model.

RWALL Forces –

     

Contact Energy –

     

Internal, Kinetic and Total Energy –

     

The plots for Rigid wall force, contact energy, internal energy, kinetic energy and the total energy are the same as discussed in the previous case.

CASE 4 – Remove both the notches and remove boundary condition on rigid body node then run the model.

First, we will remove the boundary condition. We can do this in Hypermesh but we will use HyperCrash for better understanding and visualization of boundary condition.

Note : We can also delete the boundary condition from BCS card solver in Hypermesh, but here we will remove the boundary condition by keeping BCS card in HyperCrash. Both of them will give the same results.

Step I. In HyperCrash, Import Crush_Tube_0000.rad starter file using Import from File menu or Click and drag the Crush_Tube_0000.rad file from its location.

Step II.  Right Click on rbody_12456 under Boundary Condition and click on Edit.

Step III. Clear all the boundary conditions as follows, save it and see the changes in the model.

     

    

Step IV. Export and save the edited Crush Tube file to Radioss to a specified path from File menu.

Step V. Open Radioss and Import the saved Crush_Tube_0000.rad starter file using Import Solver Deck menu.

Now we will remove both the notches using Align Node option and aligning the nodes of elements forming notches.

Step VI. Press F7 shortcut key to open align sub-panel in node edit panel. Select nodes to be aligned as follows,

     

After aligning all the nodes, we will get the following result.

     

Step VII. Navigate to Radioss panel in Analysis page.

Step VIII. Save the model as Case_4_0000.rad in a specific folder path, tick the include connectors option and under options folder write –nt 4 and click on Radioss to run the simulation.

Step IX. Open .out Engine file from specified path and check final value of Energy error and mass error and check the values of Simulation time and Total number of cycles in the same way as mentioned in the previous cases.

Step X. Open new model and switch to HyperView from Hypermesh. Load .h3d file from specified path, play the animation and plot contour of Von Mises stress using Simple averaging method.

Step XI. Open HyperGraph 2D in a new window, load T01 file and plot the energies required.

Animation and Results –

     

In this case, after removing the notches we get plane uniform surface throughout the component. As there are no geometrical irregularity or discontinuity, the force which is applied to the upper edge gets transferred to the bottom edge and thus the deformation is seen at the bottom part initially. Then we can see the same zigzag layer by layer deformation in the tube.

RWALL Forces –

     

The Normal and Total resultant forces are comparatively less than the above mentioned cases as the boundary condition is removed. The Rwall force has a peak magnitude of 1200 kN whereas it was around 1350 kN in the above cases.

Contact Energy –

     

Due to the removal of notches and boundary conditions, the contact energy has also decreased. The peak value is 1580 J whereas it is around 1880 J in the above cases.

Internal, Kinetic and Total Energy –

     

Here, slight amount of Kinetic energy is decreased and subsequent amount of internal energy is increased due to notch removal. Thus the total energy is almost the same.

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

Steps to perform for this particular case;

Step I. In Radioss, Import Crush_Tube_0000.rad starter file using Import Solver Deck menu.

Step II. Create a new notch in the middle portion of the model and remove all other notches using align node command as shown below.

     

Step III. Navigate to Radioss panel in Analysis page.

Step IV. Save the model as Case_5_0000.rad in a specific folder path, tick the include connectors option and under options folder write –nt 4 and click on Radioss to run the simulation.

Step V. Open .out Engine file from specified path and check final value of Energy error and mass error and check the values of Simulation time and Total number of cycles in the same way as mentioned in the previous cases.

Step VI. Open new model and switch to HyperView from Hypermesh. Load .h3d file from specified path, play the animation and plot contour of Von Mises stress using Simple averaging method.

Step VII. Open HyperGraph 2D in a new window, load T01 file and plot the energies required.

Animation and Results –

      

In this case, the deformation is seen initially at the notch position because it causes geometrical irregularity and thus the stress formation is higher in that area. Then the lower part of the tube deforms completely as the bending forces is transferred to the bottom. After complete deformation of lower half, the upper half starts deforming until the tube is completely deformed.

RWALL Forces –

     

The Normal and Total resultant forces in this case is higher than the other cases. Here the peak magnitude is 1400 kN whereas it was less than 1400 kN in all the other cases. This is mainly due to the notch loaction on the tube.

Contact Energy –

     

The Contact energy is also than the other cases. The peak value is 2050 J whereas it was less than 2000 J in all the other cases. Again this is mainly due to the notch loaction on the tube.

Internal, Kinetic and Total Energy –

     

Again we can see some slight changes in the profile of Internal energy, kinetic energy and total energy plot comparing other cases.

CASE 6 – Create a new notch with nodes only from opposing 2 faces and run the model.

Steps to perform for this particular case;

Step I. In Radioss, Import Crush_Tube_0000.rad starter file using Import Solver Deck menu.

Step II. Create new notch on the opposing two faces of the model and remove all other notches using align node command as shown below.

      

Step III. Navigate to Radioss panel in Analysis page.

Step IV. Save the model as Case_6_0000.rad in a specific folder path, tick the include connectors option and under options folder write –nt 4 and click on Radioss to run the simulation.

Step V. Open .out Engine file from specified path and check final value of Energy error and mass error and check the values of Simulation time and Total number of cycles in the same way as mentioned in the previous cases.

Step VI. Open new model and switch to HyperView from Hypermesh. Load .h3d file from specified path, play the animation and plot contour of Von Mises stress using Simple averaging method.

Step VII. Open HyperGraph 2D in a new window, load T01 file and plot the energies required.

Animation and Results –

     

In this case, again the initial deformation happens at the location of the notch. The two opposite notched faces deforms inwards and the faces adjacent to them deform outwards which again follows up with zigzag layer by layer formation. Then the lower part deforms followed by the deformation of upper part.

RWALL Forces –

     

The Normal and Total resultant forces in this case is slightly higher than the previous case and highest among all the cases with peak magnitude of around 1420 kN.

Contact Energy –

     

The Contact energy is also the highest among all the cases with peak value of 2130 Joules.

Internal, Kinetic and Total Energy –

     

Again we can see some slight changes in the profile of Internal energy, kinetic energy and total energy plot comparing other cases.

RESULTS :

Comparing all the six cases, the Total number of cycles, Energy error, Mass error and Simulation time are entered in a tabulated format below.

CASE No.	Total number of cycles	Energy Error	Mass Error	Total Simulation Time (in seconds)
1	83469	-4.6% to 0.0%	0.00%	119.10
2	83469	-4.6% to 0.0%	0.00%	121.16
3	82166	-4.5% to 0.0%	0.00%	87.67
4	78397	-3.7% to 0.0%	0.00%	111.70
5	85177	-4.6% to 0.0%	0.00%	69.94
6	74092	-4.9% to 0.0%	0.00%	65.97

Here in all the cases, Type 7 interface is used which is modeling contact between a master surface and a group of slave nodes. The minimum gap for impact activation or Gap_min is set to 1mm, there is no initial penetration in the model and the gap between the parts is 2.1mm which is maintained. As the tube is crushed under load, due to self-impact the nodes try to enter the defined gap and due to this, the resistive forces are activated between master segment and slave nodes. This is the cause of energy dissipation or negative energy error. The Type 2 interface defined in the model is generally used for weld connections.

In case 2, we used Inacti = 6 but got the same animation and plots. The only change was observed in simulation time as initially the node is slightly depenetrated and gap is adjusted which helps in reducing the calculation and thus we find slight increase in simulation time due to some initial work. In case 3, as there is no boundary condition on the model, less simulation time is consumed for analysis and calculation.

The cases involving notch geometry have somewhat different results in terms of animation, plots, energy error, simulation time and total number of cycles. Different notch geometry has different deformations and thus different forces and energies related to the deformation.

CONCLUSION :

We have studied the two basic and different types of contact interfaces which are Type 7 and Type 11. So these interfaces along with other interfaces are used based on the type of impact. Along with that, we have also studied the difference caused in the analysis due to notch geometry. In general, based on notch geometry, we can conclude that the geometrical irregularities present in any model accounts for stress concentration and thus failure of the model under applied load.