Simulating a Roof crush analysis as per FMVSS 216 using RADIOSS solver.

OBJECTIVE: To set up and run a Quasi-static Roof crush resistance analysis on a reduced model of a Neon car as per FMVSS 216, to plot the force vs. displacement curve and to check that the FMVSS 216 target load of ( 3 * GVW) has been met.

PROCEDURE:

1. Solver-deck set-up
   1. Import the reduced model of Neon into Hypercrash. The unit system chosen is Kg, mm, ms, kN.

      Fig 1. The imported reduced model

   2. Check for unconnected parts by using the Quality menu. There are a few unconnected parts. All these parts need to be connected appropriately. On further checking the model, some incompletely connected regions were discovered. These parts were also connected properly using springs to prevent them from flying around during the simulation and proper force transfer between the parts.

      Fig 2. Connectivity check

   3. Apply a gravity load of 0.00981 mm/(ms)^2 on the whole car body.

      Fig 3. Gravity load of 0.00981 mm/(ms)^2

   4. The model has some already created Contact interfaces. Delete these interfaces.
   5. A self contact interface type 7 was created using recommended parameter values. This contact will serve the purpose of recording the forces on the car body at the time of the roof crush.

      Fig 4. Contact interface type7

   6. Import the given model of the impactor. Perform the required transforms to the impactor at the time of import. The impactor is now placed as per the FMVSS 216 Regulations.

      Fig 5. Test set-up as per FMVSS 216

   7. A spring has been created on the impactor to measure its displacement. A boundary condition was applied to the free end of the spring to completely fix it. The elongation of the spring will give the displacement of the impactor.
   8. A boundary condition was imposed on the master node rigidising the right side of the model.
   9. A boundary condition was imposed on the shock towers in the Z direction to compensate for the absence of tyres and shock absorbers in the model.

      Fig 6. Boundary conditions

   10. A moving skew was defined on the impactor such that the Z-direction is perpendicular to the impactor face. A boundary condition was imposed on the master node of Impactor slave nodes to restrict its motion in all directions except along the Z-axis of the moving skew created.
   11. An imposed displacement was defined on the impactor master node such that the impactor moves from 0mm @ 0ms to 200mm @ 200ms. This helps in preventing any abrupt changes in the acceleration of the impactor.

       Fig 7. Imposed displacement on the Impactor

   12. A contact interface type 7 was created, keeping the impactor as the master and the car body as the slave. This helps in achieving the crushing interaction between the impactor and the car.

       Fig 8. Impactor-car interface created

   13. Set the Run time as 200ms

       Fig 9. Run time

   14. Set the time step controls as required.

       Fig 10. Time step control

2. Result request
   1. Record the TH for the impactor spring, the contact interfaces. This data will be used in plotting the Force vs displacement curve.

      Fig 11. TH requests made

   2. Request for the required contours by using the Anim/vect and Anim/elem flags in the control cards.

      Fig 12. Contour requests made

3. Model check
   1. Check the model for penetrations.

      Fig 13. Penetration/intersection check

   2. Check the model for connectivity.

      Fig 14. Connectivity check

   3. Run the model checker. The model checker came up with some warnings but no errors. Most of the warnings were related to the node groups and surface groups that were unused in the model. All these unused groups were suppressed to remove the warnings.

      Fig 15. Model checker

   4. Now that all the checks have been made, we can export the solver deck and run the analysis in the Radioss solver manager. Use parallel arithmetic for using parallel tasking.
   5. Check for energy error and mass error in the engine out file (0001.out). The errors are within acceptable limits. So we can proceed to post-processing by generating the required contour and TH plots.

      Fig 16. Error check

RESULT:

1. The animation shows the impactor pressing against the car and thereby applying a Quasi-static load on the car. The car can be seen getting deformed due to this load.
   

   Fig 17. Roof-crush animation

2. Displacement contour: The displacement contour generated during the analysis is shown in figure 18. An imposed displacement of 200 mm is applied on the impactor.

   Fig 18. Displacement contour

3. Vonmisses stress contour: The von-misses stress contour clearly shows the stresses getting developed on the structure as the impactor continues to press against it.

   Fig 19. Vonmisses stress contour

4. Force vs displacement plot: The plot resembles the expected plot. The total vehicle mass is 175 kg = 1716 N. For the vehicle to pass the Roof crush test, it has to have the capability to withstand loads equal to 3 times its own weight, which in this case is 3 * 1716 = 5150.2 N or 5.15 kN. The peak force registered for the simulation is 14.497 kN which is well above the calculated value. Thus the model has passed the Roof crush test successfully.

   Fig 20. Force vs Displacement plot

5. Energy plots: Total energy and Internal energy can be seen increasing steadily with run time. The hourglass energy is zero throughout the run time.

   Fig 21. Energy plots

CONCLUSION:

1. The solver deck was set-up for the Roof crush analysis as required.
2. The force vs displacement graph was plotted and a maximum force of 14.49 kN was noted. Since this force is very higher compared to the 3*GVW value for the car, the roof crush test is a success.
3. The energy plots were also plotted for the simulation.

Find the simulation files here.