## FRONTAL CRASH ANALYSIS OF CHRYSLER S NEON MODEL

FRONTAL CRASH OF CHRYSLER NEON

The Chrysler Neon is a front-engine, front-wheel-drive compact car introduced in January 1994 for the model year 1995 by Chrysler's Dodge and Plymouth divisions in two and four-door body styles over two generations.

BIW :

BIW (Body in White) is a stage in automotive design and manufacturing. BIW refers to the body shell design of an automotive product such as cars. It is just a sheet metal welded structure. BIW will not have doors, engines, chassis or any other moving parts.

OBJECTIVE :

The main aim of the project is to run the simulation for the frontal crash of Chrysler's Neon and record the following errors and energy changes.

EXPLANATION:

• The single unit system is followed [Kg mm ms] for the entire simulation.

CONTACT INTERFACE :

• Type 7 contact interface is used and the following parameters are set.
• The important interface parameters are

Igap      ----      Determines how the size of the gap is calculated

Gapmin  ----      Minimum gap for activation of the surface

Inacti     ----      Action to take if any initial penetration occurs

Istf         ----      Affects how the stiffness of the interface is calculated

Iform     ----      Friction Formulation

STmin    ----     Minimum stiffness to use in the interface

Idel       ----      What to do with the slave node and master segments if the elements get                              deleted

Igap : 0

• It is a constant gap method
• The gap is defined by Gapmin and is constant for all the contact. This is the default value.
• If the Gapmin value is not defined or not set, then Gapmin = min(tm,lmin/2)

Igap = 1

• It is a variable thickness method
• The gap varies according to the movement of the master surface and slave node
• the variable gap = max[(tm,(gs+gm)]
• This case will not give you an accurate result because the variable gap may not be correct all the time.

Igap = 2

• It is a variable thickness with scale factor

Igap = 3

• It is a variable thickness with a scale factor as well as the mesh size factor.
• The scale factor helps to avoid the resistive force in case if there is any kind of initial penetration.
• The mesh size factor helps to make mesh finer so that it creates the possibilities of all the node gap is detected or penetrated into the master surface gap
• Igap = 3 is preferred.

Inacti : Action to take if initial penetration exists

Inacti: 0

• No action takes place and running the simulation even though there is any initial penetrations.
• This is the best option if it is possible.

Inacti: 3

• Automatic removal of the initial penetrations
• It destroys the model geometry.

Inacti: 6

• The gap is reduced and scaled.
• When the scale factor is provided, the solver tries to reduce the gap that it won't affect the geometry and making it considered.
• Thus resulting in the best accuracy.

Iform : Sliding force computation

•  Iform = 1, viscous method
•  Sliding forces are computed using viscous parameters of the interface.
•  Iform = 2, Stiffness method
•  Sliding forces are computed using stiffness parameters of the interface, usually results in a bigger time step.

Idel :

• Idel =0, the master node and slave node are kept as such leading to instability of the simulation and the model
• Idel = 2, the master segment is removed from the contact when the link is deleted and the slaved node is deleted when it is free from the contact.

thus the recommended parameters used are

RIGID WALL :

• The plane rigid wall is created normal to X-axis to the frontal car.
• The co-ordinates of the rigid wall are (4600,0,500).
• Friction parameter is given as 0.1
• Dsearch is 1000mm which means it creates a search tolerance level of 1000mm around the rigid wall.

• The mass is added to the system such a way the total mass of the system must be 700kg throughout the system.
• At initially, the total mass of the system was 182kg. The mass is to be increased but the center of gravity of the car must lie in the back of the driver seat and must be low almost to the base of the car.
• So the mass is added along the base of the cars and the b-pillar of the car to increase the mass.
• Thus the center of gravity is almost maintained behind the driver seat and mass is brought up to 700Kg.

INITIAL VELOCITY:

• The initial velocity is given to the car thus it creates an impact with the rigid wall at some speed.
• The initial velocity of the car is given as 15.636 mm/ms along the X-axis according to the global axis.
• The entire nodes of the cars are selected.

TIMESTEP :

• The time step of the simulation is maintained at  0.5 to 0.1 milliseconds.

OUTPUT REQUEST:

1. Sectional force in the rails at the location of indicated node 174247.
• At first, the section is created using a parallelogram plane at the node id 174247.
• The node location is below the shotgun region of the car.
• The sectional forces are calculated for that node by creating a separate Time History file.

SECTIONAL FORCES AT NODE(174247)

It is noted that at node 174247, the sectional forces are keeping increasing due to the impact of the car on the rigid wall. The reaction force is applied to that particular section. To resist the reaction force, the internal resistance is created. Thus the resistance force keeps increasing and maximum at the point of 15 milliseconds which has 205 Newton.

After reaching the maximum point, the forces keep decreasing due to the deformation of the material. This is where the reaction force is more and could not able to resist by the material. so which leads to the major deformation of the elements.

After the time of 27 milliseconds, the internal forces keep increasing at a smaller rate because the reaction force is much reduced compared to the initial stage

2.The axial force received on the rails from the bumper.

• The separate TH is created for the interface and the following changes are recorded.

AXIAL FORCE

The axial force remained constant until 4 milliseconds which meant the bumper getting impacted on the rigid wall.

Then the force increases due to the resistance from the rail elements and decreases due to the small deformation and due to greater impact more reaction force is generated and which results in a resistive force which increased up to 10 Newton and again decreases because of the deformation of the rail element. Thus the spike is created in the curve.

After 10milliseconds there are no forces generated.

3. Shotgun cross-sectional forces.

• The cross-section is created at both the shotgun region such as on the left and right sides.
• It is created using the same section--Parallelogram and then defining the normal towards the reaction force.

SHOTGUNS

After the impact due to the reaction forces, the internal forces keep increasing and after the time of 20 milliseconds, the resistance force decreases which results in slight deformation at the start end of the shotgun.

And increases after 33 milliseconds and hit the maximum force of 137.3 Newton, this is due to the resistance force offered by the material due to the reaction forces. Thus the reaction forces are more thus it results in deformation and the resistance forces got reduced drastically.

The forces at the left side of the shotgun are lesser compared to the right side of the shotgun is because the mass is added more on the right side of the car.

4.A pillar cross-section

• Likewise the shotgun, the section is created at left and right of the A-pillar
• Thus the following observation has been made.

A-PILLARS

The forces keep increasing at the start and spike is shown at the start due to the displacement till 8 ms.

Then the forces keep on increasing thus component provides more resistive force do resist deformation.  At the time of 25 milliseconds, the curve drops due to the deformation are more and produce resulting resistive force. The left side of A-pillar produces more forces than the right side because, the deformation on the right side is more compared to the left side.

The right side got twisted resulting in less resistive force.

5.Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker)

An accelerometer is created on both the base of the B-Pillars and the following observation is made

ACCELERATION

Due to the initial velocity, the elements in the B-pillar got accelerated at the high peak of 580mm/ms^2 at the initial time of impact

After the impact, the acceleration got stoped and thus the curve is decreasing.

and increases again due to the deformation in the bumper elements, the car moves slightly forward resulting in the little acceleration, it happens drastically. That is why the spike is shown and remains almost constant throughout the impact.

6.Intrusions on the dash wall 66695,66244

The sperate TH is created for the particular node on the dash wall and displacement is noted.

DISPLACEMENT

The displacement was kept on increasing until the point of impact

There are no spikes in the curve because the impact didn't create any changes in the dash wall nodes because the forces have been passed on through the rail to the A-pillars and thus not affecting the dash wall.

There is an intrusion of 75mm of the node in-dash wall to the driver's cabin.

Energy curves :

Hourglass Energy: The hourglass energy remains constant throughout the simulation. This is because of the properties assigned as Qeph= 24

Kinetic Energy:  The elements are in motion due to the initial velocity, so the kinetic energy is high and keeps reducing due to the impact of the car on the rigid wall.

Internal Energy: The internal energy of each element keeps on increasing due to the impact, the reaction force is created. Due to the reaction force, the resistive force is kept on increasing in the elements.

RESULT :

Thus the simulation of the frontal crash for Chryslers Neon is executed and the following observation has been made. It is noted that the BIW components are designed in such a way that it passes the forces away from the driver's cabin making the driver safe.

Energy Errors -- 0 to -1.5%

Mass Errors    -- 0.018 to 0.025%

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