Crash analysis on the frontal section of a BIW using Altair HyperCrash.

Objective:

Perform crash analysis on the frontal section of a BIW and obtain necessary results required.

1. Sectional force in the rails.

2. Axial force received on the rails from bumper.

3. Shotgun cross sectional forces.

4. Force on A-pillar cross section.

5. Acceleration curve from the base of B-pillar.

6. Intrusions on the dash wall.

Setup:

1. A basic check of the unit system is done by accessing the starter file of the model. The unit system in use is [Kg mm ms].

2. A TYPE7 interface is created by using the following recommended values and 0.2 friction.

3. A penetration check is conducted to make sure there are no intersections and penetrations in the model.

4. A rigid wall of 0.1 friction is created.

5. The weight of the model is at 188kg. To attain the target weight of 700kg, a number of different masses are to be added to the model keeping in mind the area at which the COG has to be present.

7. Assign an intial velocity of 15.65 mm/ms (35 mph) in X-direction.

8. Model checker is used to ensure there are no errors and major warnings in the model.

On analysing the model, there were a few errors in some of the spring elements of the model. All such errors were rectified by using recommended corrections.

9. A time step(Tfreq) of 0.0005 ms and the run time is set at 80 ms.

10. To receive forces on different locations of the model as stated in the objective, cross-sections need to be assigned at those locations.

11. An accelerometer is placed at the bottom of B-pillar to receive an acceleration curve at that point as an output.

12. A local fixed skew is created at the location of nodes to receive the intrusions on the dash wall.

Simulation:

After successful simulation, energy error and mass error are checked whether they are in the acceptable range.

As seen above, the energy error is at -1.2% and mass error is at 3.042% which is acceptable.

Results:

1. Sectional force in the rails:

Maximum force recorded on the RH rail is 15.5kN and on the LH rail is 10kN.

2. Axial force received on the rails from bumper:

Maximum force recorded on the RH bumper is 14kN and on the LH bumper is 12.6kN.

3. Shotgun cross sectional forces:

Maximum force recorded on the RH shotgun is 5.8kN and on the LH shotgun is 7.4kN.

4. Force on A-pillar cross section:

Maximum force recorded on the RH A-pillar is 4.55kN and on the LH A-pillar is 4.125kN.

5. Acceleration curve from the base of B-pillar:

The maximum acceleration reached at the base of a B-pillar was 3.7 mm/ms^2.

6. Intrusions on the dash wall:

The average displacement of the dash wall was 800mm.

7. Energy graph:

According to the graph above, as the simulation progresses the kinetic energy decreases and the internal energy increases. A small fraction of energy is lost due to hourglass energy. Contact energy increases across the simulation at a constant rate.

8. Von Mises stress:

9. Displacement:

Conclusion:

According to the forces observed through the graphs above, the first peak force is acheived in rails, shotgun and A-pillar respectively. This shows the flow of forces through the BIW. Rails and shotgun are designed to crumble downwards hence absorbing maximum force from the impact. Bumpers, rails and shotgun absorb the maximum amount of energy in a frontal crash, hence, their importance in safety regulations is the highest.