To perform a Front Impact analysis of non-linear explicit nature on a partial BIW model and study the distribution of impact forces

Objective:

To perform a Front Impact analysis of non-linear explicit nature on a partial BIW model to study how the impact forces are distributed through the structure to prevent damage to the occupants.

Analysis Setup:

• A Partial BIW model is checked for necessary inputs with recommended parameters.
• Contact interfaces of Type 7 are defined with given parameters to make sure of zero penetration.
• Masses are added to mimic occupants and seats for 4 people in a vehicle.
• An initial velocity of 15.64 mm/s is applied as given.
• Sections and accelerometers are defined where the time history is to be studied.
• Rigid bodies are defined where zero deformation is expected.

Highlights:

• The Unit system for the analysis is [kN Kg mm ms].
• Deleting the previous contact interfaces, new(Type 7 )interfaces were created to cover specific parts:

1.A global Interface.

2.An interface to monitor contact forces between bumper and BIW.

3.An interface for the front crumple zone.

4.A pillars interface.

5.Floor interface.

Contact interfaces:

• Recommended parameters were used to define the interfaces ensuring zero penetrations.

Rigid Wall Creation:

• Similar to the 300k node model of the complete vehicle a rigid wall is created .

Mass Balancing:

• As required type 1 mass is added to mimic driver and passengers’ mass on the floor. This adds up to the K.E. And needs balancing as Centre of Gravity point affects how the vehicle will behave on Impact.

Debugging and Error limiting :

• To ensure good accuracy model checker was run before going ahead with the analysis. Small errors regarding free nodes and unnecessary joints, contacts were resolved.
• From the 0000.out file it is deduced that the mass and energy errors are within limits.

Results:

1. Max Von mises stress is seen in the region where max. Plastic strain is at the root of the rail, on the firewall where due to crushing of the rails which is the main part of the crumble zone a small part of the force is transferred to the thin firewall.

Mass Balancing:

1. The effect of having a biased COG for either Left or Right hand drive car can be seen in the slight difference of results.

Contact Forces at Bumper: LHD case

• For the LHD case as seen in the displacement comparison a 5.6N resultant force on the right side is recorded. Asymmetric deformation of the crumple zone can be seen from the graph.

Contact Forces at Bumper: RHD case

• In the RHD case the distribution with respect to time is similar in nature to the LHD case with smaller peak values of 3.3N for left side and 5.5N for right side interface.

Sectional forces and the corresponding plots are discibeded in the ppt summery :

https://drive.google.com/open?id=1O96XjtozSi9Y-mdJQ0rd3KDJqht26pAP

Conclusion:

• As per design the BIW structure works to dissipate the impact energy by crumpling/crushing as well as transfers it around the occupant chamber such that least damage is done to the passengers and driver in case of a crash.
• As the given model is only a part of the complete assembly as in the 300k element model many of the important components such as engine and transmission in case of a front wheel driven vehicle, steering and suspension system, body panels etc are not involved which in real life conditions will dissipate more of the impact energy lowering the impact forces further hence the results are satisfactory.
• However the added mass of these uninvolved components will result in higher K.E. Causing larger deformations hence, it can be assumed as a trade off. So further analysis is suggested for assurance.
• As seen in the result plots for sectional forces and intrusions, the given model is a safe BIW design.

Google link to folder with all the files:

https://drive.google.com/open?id=1aO5tqUlaih5_84VuIe5Uh4LciuVDQpfb