To perform side impact analysis on a partial BIW model as per the Euro NCAP standards for velocity, positioning and dimensions

Objective: To perform side impact analysis on a BIW model minimised as per the Euro NCAP standards for velocity, positioning and dimensions

The Setup: A 10 Inches thick pole is used as a rigid wall, impact occurs with the BIW model travelling at 32Km/hr or 8.9mm/ms such that the horizontal centreline of the model makes a 75 degree angle with pole.

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 8.94mm/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 for the front crumple zone.

3.A couple of interfaces for the door and body.

4.Floor interface.

Contact Interfaces:

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

Rigid Wall/Pole Creation:

As per EURO NCAP standard, rigid wall is created with 254mm diameter. The initial velocity is defined such that the impact happens at 75degree angle (Between Horizontal vehicle centreline and pole.) Zero Initial penetration is ensured.

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:

• 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. Rwall reaction forces: The plot shows an average reaction force of around 37N and a spike at 32ms of 60N.As stated previously the impact occurs at an angle as a result the floor members aren’t loaded directly. At the 33ms mark the vehicle deforms such the members get deformed directly and hence the wall/pole experiences a higher resistance. As the momentary deformation ends the force goes down too. In conclusion a lot of energy is absorbed by the door frame and the body surrounding it till the floor members get in the picture.

2. Energies: As seen in the previous project the end time for the analysis isn’t sufficient for the total deformation of the complete model hence the K.E. And I.E. Plots aren’t complete. However their nature is symmetric and the contact and hourglass energy are minimal, hence the solutions can be considered acceptable.

Stresses and strain:

• Max.Von mises stress is seen in the region where max. Plastic strain is(till the last time step – at the corner of the rear window frame where the actual impact occurs), at the other edge of the floor member 1.The Max stress comes out to be 324 MPa. which is realistic and manageable.

Sectional Forces and intrusions are explained in detail in the ppt:

https://drive.google.com/open?id=1bDkNS8tvET0ha_wjoJOnpfnyWZcg70Xy

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 roof panel, floor components, body panels etc. are not involved which in real life conditions will dissipate some 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, only a fraction of the impact forces are transmitted to the inner structural components, hence the design can be considered safe.

Drive link to folder containing all files:

https://drive.google.com/open?id=1G37LBdZj7lExhIkzFbe_sO_ILjlx0HCT