Assignment 7-Side Pole Crash Simulation Challenge

AIM: The main aim of this challenge is to study the forces in cross members, peak velocity of the car door and intrusions in case of side crash analysis.

OBJECTIVE: The objectives of this challenge are as follows:

1. To create required interfaces and rigid pole.

2. To add mass to the model to reach target of 700kg and maintain the CG about required range.

3.To create sections and springs to measure forces and intrusions.

PROCEDURE:

1. The neon_side_reduced_0000.rad file can be imported by using import solver deck option.

2. Unit systems can be checked by selecting the begin car (SOLVERà CARDSàBEGINCARD).

3. Type-7 and type-11 interfaces are created with recommended properties.

4. No intersections were found in the given model and the penetrations were taken care by using inacti option while defining the contact.

5. check for connectivity (TOOLSàFIND CONNECTIVITY). All the free parts are connected.

6. Plane cylindrical rigid pole is created with the properties shown in the below image.

7. Mass is added to the model to achieve a total mass of 700kg and COG was maintained at desired location.

8. Initial velocity of 8.88 mm/ms in y direction is applied for the whole component.

9. Model checker (TOOLSàMODEL CHECKER) was used to find the errors in the model. Empty sets and empty admass were deleted.

10. Interface and nodal time steps were maintained at 0.5 micro seconds with a scale factor of 0.67.

11. Run time of the simulation was maintained at 80ms.

OUTPUT REQUESTS:

1. A section was created on the cross member and a frame was assigned to it to determine the peak value of the force passing through the cross member with respect to time.

2. Same procedure was followed for creating sections on another cross member and final sections are shown in the below image.

3. Springs were created to find out the intrusions of fuel tank, B-pillar, and hinge pillar with properties as shown in the below image.

4. Movable skew was created on one of the elements of the door to find out the peak velocity of the door during crash.

5. Time history Output cards were created for intrusions, sections, and nodes.

RESULTS COMPARISION:

Energy and mass errors:

Energy and mass errors were found to be -1.4% and 0.024% respectively at the end of the simulation and they are well within the acceptable range.

Variation of IE, KE, TE, CE, HGE, R-wall forces& Contact forces:

Kinetic Energy: Since the car was having some initial velocity of 8.8mm/ms, the car was having some KE at the starting of the simulation i.e. at 0ms and the same thing was depicted in KE variation graph. As there was no crash in first 5ms, the variation in KE was almost negligible. As soon as the crash happened between car and rigid pole, KE of the car decreases because of the deformation in the car. The value of the KE decreases linearly from starting to the end of the simulation because of continuous deformation of the car.

Internal Energy: The amount of work done to deform a body will be stored as energy inside the body and this energy is called internal energy. If the deformations are more, body will have more internal energy. Initially as there is a clear gap between the car and rigid pole, there was no deformations in the car, therefore the internal energy started from zero at 0ms.Since there was no collision in the first 5ms, the value of internal energy was very negligible from 0-5ms. As the simulation time increases, the deformation in the car also increases leading to increase in internal energy till the end of the simulation.

Total energy: The total energy of the system should always remain constant. Negative error represents that energy has been dissipated from the system. In this case a slight reduction in total energy of 1.4% was observed by the end of the simulation. We can also observe the same thing i.e. negative energy error in the 0001.out file. Presence of contact and hourglass energies in the system was responsible for this imbalance in the total energy. The energy error was well within the acceptable range and total energy started from the high value because of higher value of KE.

Contact energy: Energy lost in overcoming the penetration is known as contact energy. Initially there was no deformation in the car and no self-contact was observed, because of this reason contact energy started from origin. As simulation time progresses, the deformation in the car increases leading to self-contact of the car which in turn increases the value of contact energy. The contact energy variation was almost linear throughout the simulation.

Hourglass energy: Energy spent in overcoming the hour glass effect is known as hourglass energy. For all the components QEPH element formulation was used, but still we can see we can see very few elements were undergone hourglass effect. Improper mesh size in some of the components at some places lead to hourglass effect. Remeshing the elements and maintaining proper mesh where the elements were subjected to hourglass effect can help us to eliminate hourglass energy from the system.

Rigid wall forces: Rigid wall forces are the reactionary forces that are acting on the rigid ball. R-wall forces started from zero because there is no crash initially. As soon as the crash took place R-wall forces reached to a peak value of 31KN around 9ms and later those forces were transferred to car. Any rise /dip in the graph can be attributed to increase/decrease in the contact area between the car and rigid pole.

Contact forces: Resisting forces applied to overcome the penetrations are known as contact forces. Since there was no contact initially, we can see the contact forces were starting from zero. As the deformations increases, elements will try to come into contact with each other and requires higher resisting forces to separate them. A peak value of 23.34KN at the end of the simulation was observed for type-7 contact because of the larger deformations in the body. We can notice contact force was continuously increasing with respect to time in the type-7 contact graph. As we can see from the type 11 contact force variation graph, very less resisting force is required to remove edge to edge penetration compared to the resisting force required to avoid node to surface penetration. Defining type 11 contact helps us to slightly reduce the node to surface penetrations during the simulation.

OUTPUT REQUESTS:

Axial forces on cross members: Cross members are very important components because they will take most of the forces during the side impact. Since the front cross member is connected with springs to rocker arm, and because of the initial velocity applied to the car there can be relative motion cross member and rocker arm leading to development of small residual forces before even impact took place. Due to presence of residual forces in front cross member the graph started at 1.25KN at 0ms.Whereas if we look at the mid rail cross member it is connected to rocker arm with rigid body, in this case there is no chance relative displacement between the mid rail and rocker arm and because of this the graph started from zero for mid rail crossmember. As the simulation time increases, the forces in both the cross members increased due to crash. The max values of front cross member and mid rail cross member were found to be 4.35KN and 4.79KN respectively. Higher value was observed incase of mid rail compared to front cross member because it was inline with the rigid pole and coming into contact with the rigid pole during the crash.

Intrusions: The amount of shrink in the structure during the crash is known as intrusions. The max intrusions in fuel tank, B-pillar and hinge pillar were found to be 512.52mm,481.94mm and 29.93mm respectively. All the 3 types of intrusions attained the peak value at the end of the simulation because of higher deformations in the car. Fuel tank intrusion is very high compared to the other 2 types of intrusions, so to reduce this intrusion at the fuel tank we can introduce one more cross member near the fuel tank region. The added cross member will absorb some force and undergoes some deformation and this can lead to decrease in the value of intrusion.

Peak velocity of the door: During the side impact the door gets deformed and in this process the inner portion of the door might hit the passenger and can cause injuries, so it is very important to know the peak velocity on the inner portion of the door. Since the car has initial velocity of 8.8mm/ms, the graph also started at 8.8mm/ms at 0ms.Once the crash took place, the velocity got decreased. Max velocity was found to be 9.10mm/ms right after the impact.

Simulation:

Max von mises stress was found to be 0.34 Gpa.

CONCLUSIONS:

Ø Side crash analysis was performed on the given BIW model and forces on cross members has been studied by creating sections along with the study of intrusions and peak node velocity of the door.