A study on different Contact Interface Models

A study on different Contact Interface Models

Objective:

To study, analyse and compare the different contact interface and the impact of a notch in the structure during crash.

Procedure:

Step 1: Import the solver deck (.rad) file and ensure all the recommended shell properties are assigned.

Step 2: Make a new directory/folder and run the simulation, so that the new files for each case are organised.

Step 3: Then create split window layout to accomodate HyperView and HyperGraph 2D, to open and read data .h3d and T01 files in respective layouts.

Step 4: Save the Report Template. And tweak and modify the appropriate necessary values for the next case and run the simulation in a new folder.

Step 5: Once the simulation is done, don't load the results or plot the graph rather continue with the simulations for the specified different cases.

Step 6: On completion of all simulation runs, open the result template and open the .h3d and T01 files to read and analyse the data, easily.

Step 7: The result data is then tabulated and compared to fetch the results.

Simulation Data:

The different cases studied in this assignment is tabulated below.

The simulations are run with following parameters, Tstop = 30 ms, Tfreq = 1 ms, Nprint = -100. The different cases of simulations are executed and the runtime and simulation data are compared. The energy and mass error values are well below the accepted limit of 15%. The mass error remained at zero as there was no mass added to or removed from the model.

The different energy values such as Internal, Kinetic, Total and Contact for each case is plotted using HyperGraph 2D. The internal, kinetic, total and contact energy values of the simulated cases are charted out for comparison, however the hourglass energies remained at zero throughout the runtime across different simution cases.

The maximum resultant rigid wall forces and the time at which the maximum are recorded are tabulated.

The Von-Mises Stress and Contact Forces contours are created using HyperView and we can also animate the simulation to study the nature of the deformation or impact.

Observations:

The snapshots of the contact forces and stress contours are captured at a timeframe of 3rd and 30th ms respectively, to depict the onset of deformation at 3 ms and the end of the deformation at 30 ms.

Case 1

The TH/Part for all the parts are created to compare the results.

In this case, the contact is modelled using only Type 7. The simulation is executed without modifying, and the outcome is used as a base for the next two cases.

The contact energy is max at the same time (26.6000709533691 ms) when the rigid wall total resultant force is at its peak value.

From the contours, it can be seen that the notch in the crush tube becoming the exclusive region for the onset of deformation.

Case 2

The Inacti parameter used to manage the initial penetrations is set to 6, which means the existing penetrations is removed by reducing and scaling the gap.

The simulation is run with Inacti=6, since there is no initial penetrations found in the structure, the values and outcome remains same.

Case 3

The Type 11 (Edge to Edge) Interface is also created and assgined in addition to the existing Type 7 (Node to Surf) Interface. This will capture even if the edge lines intrudes into the gap, leading to more accurate results, accomplishing the drawback of Type 7 interface. The Type 11 Interface card image with parameters is added.

As a result of Type 7 and Type 11 combination, there is an increase in the Contact Energy value and the energy error also, compared to the previous cases. This is because the edge to edge interface, which are captured in the previous case were contributing to the internal energy, but in this case they contribute to the contact energy. The energy error formulation/calculation doesn't involve the contact energy values, so the internal energy is lower compared to the previous cases and it leads to the increase in energy error also.

Apart from the difference in the energy error and other energy values, there is a marginal increase in the total resultant rigid wall force, but the time at which the total resultant rigid wall force reached its peak value remained almost same. The contact forces value is increased comapred to the previous cases.

Case 4

The boundary condition (that allowed only z-translation and constrained all other translation and rotational motions) is removed also the notch present in the structure, using the align nodes option in HyperMesh.

Now, the simulation is executed. The absence of notch and BCS has reduced the contact energy since the magnitude of structure buckling is reduced, that can be observed from the animation. Because of reduced self contact, the energy error also decreased, since the internal energy remained as same and not get translated into contact energy, as the crush tube deformed.

The peaking of rigid wall forces also delayed compared to the previous cases.

Case 5

The notch is created again, around the structure in the middle by using HyperMorph and the case in simulated.

The outcome describes the presence of a notch and its impact on the deformation. The difference between the notch present in the previous 1,2,3 and 4 cases also reflected here.

When compared to the case with no notch, the contact forces has increased since the notch became the exclusive region for buckling, so the contact forces and the resultant rigid wall force have increased.

Case 6

In this case, the notches (similar to dents) are created on the opposite faces of the tube towards the rigid wall, in addition to the existing notch at the middle, using translate nodes option in HyperMesh.

The presence of additional notchs also reflected in the results of the simulation. And the energy error and the contact energies varied compared to the previous case.

Results and Conclusion:

• The Cases 1, 2 and 3 talk about the Type 7 and Type 11 interfaces and how the combination of both type of interfaces, improved the results. Also, in case 3, the addition of Type 11 interface reduced the stiffness of the body, thus decreasing the energy error and a marginal increase in the contact energy as the edge to edge contacts are also captured.
• The Cases 4, 5 and 6 depict how the presence and position of notch impact the deformation of the crush tube. And, from every case, we can see the deformation begins at the notch region and a stress concentration is occuring to an extent.
• The removal of boundary condition also impacts the outcome of the crash analysis.

Meshing the Bumper Assembly

The bumper assembly model is meshed with a target element size of 6 mm and a quality criteria with optimum parameters are also created to ensure no meshed elements failed. The assembly parts are then connected using different connectors like spot and seam welds. The snapshots of the meshed bumper assembly are added.