FRONTAL FIXED OFFSET BARRIER TEST

ME 8020

Siddhesh Ozarkar- fr8695Yogesh Tupe - fx3474

FRONTAL OFFSET IMPACT• The Frontal Fixed Offset Rigid Barrier Test, often called the offset

barrier test, subjects the vehicle/occupant restraint system to partial engagement of the front structure with a rigid barrier face.• The offset barrier test produces a lower acceleration crash pulse of

longer time duration than the full frontal fixed rigid barrier test frequently characterized as a “soft” pulse. • It is a full systems test which evaluates the response of the energy-

absorbing vehicle structure and the occupant restraint system to a low severity crash pulse.

SIGNIFICANCE OF FRONTAL OFFSET IMPACT TEST• The offset barrier test is intended to represent most real world crashes with less

frontal engagement-in perpendicular impacts with change in velocity up to approximately 56-60 km/h based upon an impact speed of 56 km/h.• This test frequently results in significant occupant compartment intrusion in

current production vehicles. The test is intended to evaluate air bags/passive restraints to assure occupant protection in more than just the longitudinal direction. • It requires that vehicle designs prevent serious head contact with A-pillars, roof

headers, and other components of the upper interior structure of the occupant compartment. • The test provides the capability to evaluate upper and lower leg protection due

to localized intrusion.

Kinetic Energy of Crash• The kinetic energy of the crash (1/2MV^2)is dissipated by 1. Crush of the vehicle.2. Residual Rebound Velocity.3. Vehicle RotationWhere, M= mass of vehicle V= Velocity of vehicle% KE Absorbed by the Vehicle = (½ MV^2 - KE lost in Rebound & Rotation) / (½ MV2 ) x 100

Modelling and cleanup of Meshed Vehicle Model

• Element and mesh cleanup tools used in Hypermesh to generate a file that can be prepared for analysis in LS-Dyna.

• The vehicle was provided with a velocity of 10m/s and was made to collide with a rigid barrier.

Meshed vehicle model

Crumble zone of vehicle crushed successfully with kinetic energy absorption.

Reduction of Kinetic EnergyThe deformed model shows the deformation of the frontal body structure of the vehicleThe flow of stresses indicates that the frontal structure is sustaining the impact damage for the give period of time.

Vehicle with Steering Airbag, Doors and other significant components.The steering and seat components were connected to the vehicle using the beam elements.A rigid body spider or (chicken feet) were used to transfer the motion of the components like steering during the crash.

Element Spider generation for load transfer.

Successful Airbag Deployment.

Vehicle Body Crushing with seat motion along the vehicle.

Offset Impact of Full Vehicle Model Plots and Results• A successful run of full vehicle model with all significant components was

achieved.• The seat was positioned in such a way that the dummy will not be interfering

with any of the vehicle components but the seat and steering. • The seat was constrained to move along with the vehicle using beam elements

attached to the floor of the vehicle.

Kinetic energy of the vehicle

Internal energy of the vehicle

• The kinetic energy of the vehicle decreases as the energy is absorbed by the structure, rebound and residual velocity of rotation.

• The internal energy of the car is seen to be increasing. This proves that the law of conservation of momentum is followed in this collision.

Analysis Result

Resultant Displacement of the vehicle

Analysis results:

• Resultant Deformation

• Resultant Stresses

• Impact Initiation and Airbag Deployment

• Full Airbag Deployment

• Vehicle Collision

ResultsParameter Value

Internal Energy 98 MJ (at the end of impact)

Kinetic Energy 170kJ

Total Energy 210 kJ

Velocity of the vehicle

Total energy of the vehicleResultant force at rigid wall

Contact initiationPeak reaction force Crumple structure contacts the rigid wall

Velocity Starts to decreases

Drop in velocity due to Heavy Engine impact with wall

Ergonomic Dummy Positioning

Angle Value (degree)A 110B 30C 15D 160 (ACCORDING TO GIVEN

DIMENTIONING)

E 10

A

BC D

E

Dummy Rotated by 10 degreeDuring final positioning

Preliminary Sledge Model AnalysisA preliminary sled model was created so as to test the integrity and contact definition of the dummy with seat, steering and other essential components of the vehicle interiors.

Sledge Model Seat Structure

Dummy PositioningSteering Placement

Dummy Impact Initiated

Head Displacement

Abdominal Displacement

Feet Displacement

Knee Joint Angular Deflection

Contact Definition Integrity

No Seat Penetration

No Floor Penetration

• Contact treatment forms an integral part of many large-deformation problems. Accurate modeling of contact interfaces between bodies is crucial to the prediction capability of the finite element simulations. 

• A contact is defined by identifying (parts, part sets, and/or node sets) what locations are to be checked for potential penetration of a slave node through a master segment.

• Simple surface to surface contacts were defined in the model to observe the penetration.

• No penetration was observed in the model , this means that the contacts defined for penalty method have been sufficiently applied the resisting force and thus enabling to measure the stresses and deformations.

Energy Results

Impact Initiated

Internal Energy

Kinetic Energy

Total Energy

The kinetic energy of the system decreases and an increase in internal energy of the vehicle is observed.

Acceleration and Displacement

Acceleration StressesDisplacement

Initial

First Contact

Full Impact

Dummy Interaction & Failure Criteria Results 1

Dummy Part Deflection (mm)Head Deflection 252Chest and Abdomen 266Feet 242Knee Joint 232

Full Crash Model

Dummy In Vehicle Before Crash

Airbag Deployment after Impact Initiation

Full Impact

• Dummy interacts with the vehicle interior without interferenceWith any of the vehicle interiors.• Airbag is successfully deployed after impact and supports the dummy from smashing into the Steering wheel.

Energy Results

Internal Energy

Kinetic Energy

Total Energy

Impact

Hourglass Energy

Displacement of Model Before and After Impact

Impact Initiated

Full Impact

Dummy Rebound Response

Dummy Injury Criteria• Head Injury Criteria:Head Injury criteria was calculated from the LS-Dyna Plot. HCI for the current dummy Model with reinforced structure is 982.

Design of Experiments for Vehicle structure Enhancement

Vehicle Under Body Structure

Engine Bay Understructure• During the analysis we

observed the member A gets crushed and the load is transferred to the engine block.

• Engine block enters the Driver Compartment.

• The Lower Rails were not completely utilized during the absorption od the impact.

Member DesignationBumper Rail ALower Rail BDash Rail CUnderbody Rail DRear Body Rail E

A

B

C

D

DE

Reinforced Members of Underbody Structure

Reinforcing Member

**Reinforcing Member not Visible In the above Model (Zoom Required)

Displacement Reduction

Improved Underbody StructureOriginal Underbody Structure

Max. Disp. = 1150mm Max. Disp. = 721mm

Conclusion• Total energy of system increases. • The kinetic energy of the system decreases and an increase in internal

energy of the vehicle is observed.• Thus from the graph it can be seen that by using the laws of conservation of

energy, the total energy of the system increases with almost the same amount that of the increase of the internal energy of the system and this is equal to the loss of kinetic energy of the system.

• Dummy Injury Criteria :

• What If Study: The underbody structure was modified and reinforced with additional members to reduce the overall structural displacement.

• The Displacement is reduced around the dummy by 37%. As Obtained from the Displacement Plots for Both models.