Roof crush analysis under FMVSS 216 standards.

Objective:

Study the roof crush analysis on a model of a car and check that the FMVSS 216 target load has been met.

Setup:

Step 1: Checking the unit system being implemented to the model.

Open the starter file (_0000.rad) in to the notepad. As observed in the starter file, the unit system being implemented in this model is [kg mm ms].

Step 2: Position the impactor to the desired location.

1. 180° rotation about the global z-axis.
2. 5° rotation about the axis through axis AB.
3. 25° rotation about the axis through axis AC.
4. Translation to put point A at global (-3500.00, 584.822, 1343.06).

Step 3: Create an appropriate interface.

A TYPE7 interface with recommended properties and 0.2 friction is created where all the nodes available in the model are slaves and all the elements of the model are masters.

Two TYPE7 interfaces are created for this model. One for the self-impact within the model of the car and another between the impactor and the model.

Step 4: Check for penetrations and intersections.

In the tools drop-down menu, select penetration checker and select all the groups. It will automatically check for penetrations and intersections.

Step 5: Create rigid bodies.

Three separate rigid bodies are created on top of the each suspension shock tower nodes (ie: two in the front and one on the rear).

Step 6: Add boundary conditions (BCs).

Master nodes of the rigid bodies created on top of the suspension shock tower nodes are locked in Z-direction. Master nodes of three other separate rigid bodies (pink colour) are locked in all directions. A boundary condition is also added the free end of the spring such that its motion in all 6 DOFs are locked. This will add stability to the impactor while in motion towards the car body.

Step 7: Add a moving skew and boundary condition to the master node of the rigid of the impactor.

A moving skew is created on the master node of the rigid body of the impactor such that the Z-axis of the skew is perpendicular to the face of the impactor. Also, a boundary condition is created on the same master node such that the translation motion of the node along the Z-axis of the moving skew is allowed. Other than that, all the motions in all 5 DOFs are restricted.

Step 8: Add imposed displacement.

Another boundary condition, imposed displacement, is added to the master node of the rigid body of the impactor to avoid any abrupt changes in acceleration. This is done efficiently by adding a linear curve such that at t=0ms, the displacement of the impactor is 0mm and at t=200ms, the displacement of the impactor is 200mm.

Step 9: Time step.

A nodal time step is created with 0.1ms. Also, the run time of the simulation is set at 200ms.

Step 10: Output requests.

The following outputs are requested in the animation files.

1. Elemental energy
2. Elemental equivalent plastic strain
3. Elemental hourglass energy
4. Elemental von Mises stress
5. Nodal added mass

Simulation:

In the analysis toolbar, select Radioss solver and export the file to the desired location and let the simulation run for 200ms.

At the end of the simulation, open _0001.out file and check for energy error and mass error at the last cycle (ie. 200000).

Energy error is at -18.4% and mass error is 4.6%.

Results:

1. Force vs displacement:
2. FMVSS 216 target load:

The total mass of the model is approx. 159.74kg. As per the standard of FMVSS 216, the roof of the model should resist 3 times the force acting on the stationary model at rest.

Hence,

Target load = 3 * 159.74 * 9.81 = 4701.1482 N = 4.7kN

According to the force vs displacement, the maximum force resisted by the model was 3.5kN.

3. Energy curve:

There is an increase in kinetic energy only after the impactor collides with the model and hence the model is displaced due to the impact force. Similarly, the contact energy and internal energy is also zero until there is impact.

4. Displacement:

5. Von Mises stress:

6. Hourglass energy:

7. Nodal masses:

8. Plastic strain:

9. Specific energy:

Conclusion:

The maximum force resisted by the roof of the model was below the target load. Hence the roof of the car has failed to comply with the standards.

The reason behind the failure could be due to lack of components available in the model. Another reason could be the inefficient way of connecting the open parts using rigid bodies and also the master nodes of all the rigid bodies might not be constrained in all DOFs.