Frontal crash BIW analysis using RADIOSS

Problem Statement:

Frontal crash BIW analysis.

Objectives:

Pre-processing

1. Create appropriate interface, friction 0.2 and recommended parameters.
2. Make sure of no penetrations and intersection.
3. Correct rigid bodies if any issues.
4. Create rigid wall with friction 0.1.
5. Compare the model weight with the full scale 300k nodes model and use added masses to reach target weight 700kg while getting CG about the required range.
6. Initial velocity 35 mph.
7. Use model checker to ensure good quality.
8. Time-step :0.5 to 0.1 microseconds.
9. Run 80 ms.

Post-processing

1. Sectional force in the rails at location of indicated node.
2. Axial force received on the rails from bumper.
3. Shotgun cross sectional forces.
4. A pillar cross section.
5. Acceleration curve received on the accelerometer at base of B pillar.
6. Intrusions on the dash wall.

Unit system used:

Unit system used for analysis is "kg mm ms"

Fig No. 1: Unit system used for analysis.

1. Pre- Processing:

The front BIW portion of a car is consider for Frontal crash analysis. Initially it consists of 74 parts in three 3 assembly viz. BIW, BIW Floor and joints.With total number of nodes 9904892. The intial mass of the structure is 188kg.

1. Checking Initial connectivity:

After checking connectivity there was 2 free spherical joints of id 110013 and 110002 as shown below. Which are deleted since it was not connected to other part.

Fig No. 2: Connectivity check.

2. Initial Error Check:

After checking error there was 2 error in joints of id 110018 and 110019 as shown below. Which are deleted since it was connected to suspension system which is not included in the frontal crash analysis. By this all initial errors are overcome.

Fig No. 3: Error check.

3. Interface:

At the beginning there was 6 interfaces of type 7 used to the BIW structure. But there was no proper connection in between them as shown below. So all the interface was deleted and re created it.

Fig No. 4: Initial interfaces.

By creating single interface of type 7 contact is replaced with the above interfaces. The interface assigned with recommended properties for crash analysis as shown below. The friction in contact is 0.2.

Fig No. 5: Final interfaces.

4. Penetrations & intersections:

After creating contact interface and set them to recommended value and setting Inacti value to 6 there was 134 penetrations in the structure. All these penetrations are removed by using penetration check option in hypermesh.

Fig No. 6: Penetration and Intersection.

5. Correction of Rigid body:

There were some free nodes at rigid bodies as shown below. This rigid body was deleted since it was connected to translation joints. Which was not connected i.e. free from one end.

Fig No. 7: Rigid Body.

6. Rigid Wall

The rigid wall is created at co-ordinates 4600,0,0 and normal direction at -1,0,0. The distace for slave nodes is set to 1500mm and friction is 0.1.

Fig No. 8: Rigid Wall.

7. Mass addition & C.G.

The initial mass of the BIW structure is 188kg. The mass is added to the structure to achieve 700kg mass like a full car model. The mass is added in such a way that C.G. of the car should lie near driver's seat. So the mass is distrubuted as front seat having mass of 75kg each the back seat is having 210kg. 42 kg is distributed at rail for engine component. In order to adjust C.G. 110kg is adjusted at bottom of B pillar. The below figure shows mass distribution and location of CG. The small dot in the image shows the CG of the structure.

Fig No. 9: Mass distribution and C.G. location.

8. Initial Velocity:

The initial velocity of the car is set 35mph which is 15.64mps.

9. Run time and time step:

The run time is set to 80ms. and time step is 0.5ms. as shown below.

Fig No. 10: Run time and time step.

10. Section:

The section is created in order to calculate section force at shotgun area, Rail component, Hinge pillar, B pillar area. So this section is requested to the output block to observe the effect of force at these areas.

Fig No. 11: Sections.

11. Accelerometer:

In order to observe the acceleration graph there are two accelerometer at the bottom of B pilllar at both side.

Fig No. 12: Accelerometer.

12. Intrusion:

To observe the effect of impact at pedals there are two nodes selected at pedals. The nodes 66695 and 66244 with reference of node id 121739 and 122048 respectively are connected with a spring element with 1e-8kN/mm stiffness. As shown below.

Fig No. 13: Intrusion.

13. Model Checker:

After completing Pre-processing the model is checked through model checker. Initally there was 2 error first was error id 59 regarding property of the spring element. To overcome this error I had recreated the spring element with property card Spring P4. The second error with error id 268 "Error in memory allocation." this was due to in sufficient RAM it was also solved by deleting software of large RAMconsumption. With this there was no error only 4 warnings.

Fig No. 14: Error.

Fig No. 15: Front_crash_0000.out file.

II. Processor (Solver) :

From Front_crash_0001.out file, The Total number of cycles was 80001. The energy error is -2.0% which is in acceptable limit. The mass error is 3% which also less than 5% it is accepted. There is increase in mass which is due to reduction in time step at that node, to maintain time step the mass is increased. The run was "normal terminated" which implies the was successfully completed. There was no sudden changes in energy as well as in error. As shown below.

Fig No. 16: Front_crash_0001.out file.

III. Post-Processing:

For post processing the output requested are as follow:

1. Cross-Sections at Rail component (Right and left), shotgun (Right and left), A-pillar (Right and left), Hinge pillar (Right and left) and Fender (Right and left).
2. Accelerometer at bottom of B pillar.
3. Intrusions at pedals.
4. Contact forces.

1. Cross-Sections:

a. Shotgun (Right and left):

The area behind the bumper is shotgun. It is the area where there is maximum impact due to collision. A cross section is introduced to observe the forces as shown below.

Fig No. 17: Shotgun.

Impact on shotgun:

The below two graphs shows total resultant forces on left and right shotgun.

Fig No. 18: Shotgun Forces.

There is difference between right and left cross section of shot gun due to un even distribution of forces, pitching and yawing effect. In right cross section the resultant force is 9.078kN at t=11ms. and then there is decrease in forces but maximum resultant force of 9.11kN at t=13.5ms. Then there is decrease in forces till t=20ms and then it increases at t=30.5ms of magnitude 8.775kN at t=46ms then there is decrease in forces.

In Left cross section the maximum resultant force of 13.97kN at t=12.5ms. and then there is decrease in forces.

By comparing both side forces after t= 13 ms. there is drop in forces but in right cross section at t=20ms there is increase in forces. This is due to component right behind shotgun in right side does'nt absorb forces as shown in figure below highlighted with circle.

Fig No. 19: Shotgun Forces absorbtion right and left cross section respectively at t=30 ms.

b. Rail component (Right and left):

The below figure shows cross section of rail component. This is important since forces get transfer through rail to the main structure.

Fig No. 20: Cross section of rail component.

Impact on Rail component:

The below two graphs shows total resultant forces on left and right Rail component.

Fig No. 21: Forces on Rail component.

In right component of the rail at time t= 14.50ms. the first peak is observed of magnitude 20.20kN due to impact. then there is decrease in force at t=20ms the force start rising and at t=46ms the maximum force of 26.18kN due to bending of the components the left side is bends more compare to right ones. So these second peak in graph is not visible at left side components.

In left side rail component at the time of impact there is maximum force is generated i.e. at t=14ms of magnitude 29.72kN. Then there is decrease in forces.

c. Fender (Right and left):

The below figure shows cross section of Fender component. This is important since forces get transfer through fender to the main structure.

Fig No. 22: Fender components.

Impact on Fender component:

The below two graphs shows total resultant forces on left and right Fender component.

Fig No. 23: Forces on fender component.

In right component of the fender at time t= 28ms. the first peak is observed of magnitude 10.66kN (maximum force) due to impact. then there is decrease in force at t=45ms the force start rising and at t=50ms the of 9.99 kN. Due to bending of the components the left side is bends more compare to right ones. So these second peak in graph is not visible at left side components.

In left side fender component at the time of impact there is maximum force is generated i.e. at t=30ms of magnitude 16.54kN. Then there is decrease in forces. There is more jerks are observed in left component compare to right one it is due to collision.

d. A-pillar (Right and left):

The below figure shows cross section of A Pillar component. This is important since forces get transfer through A pillar to the main structure. In front crash analysis from A pillar there is no or negligible forces are transfered to the rear parts of the car.

Fig No. 24: A Pillar components.

Impact on A Pillar component:

The below two graphs shows total resultant forces on left and right A Pillar component.

Fig No. 25: Forces on A Pillar component.

In right component of the A Pillar there is no hike in forces at t=50ms the force of 12.98kN is occcured. The right side component the forces increases gradually till t=10ms then it becomes almost constant till 30ms. Then the forces increases due to self collision. At right side A Pillar maximum forces is transfer compare to left side.

In left side there is minimum force are transfer due to bending effect and some forces are observed by the components. The maximum forces develop in A pillar left side is 5.01kN at t= 19ms. Then it is constant till t=50ms after that it decreases.

e. Hinge pillar (Right and left):

The hinge pillar do not play as important role as in case of frontal crash analysis compare to side crash. The below figure shows the cross section of the hinge pillar.

Fig No. 26: Hinge pillar components.

Impact on hinge pillar component:

The below two graphs shows total resultant forces on left and right Hinge pillar component.

Fig No. 27: Forces on Hinge Pillar component.

In Hinge pillar very less forces are observed compare to other components. The maximum force on left side hinge pillar component is 5.58kN at t=60ms. Very less force are observed at right side. The maximum forces in the right side is 3.1kN at t=41ms .

2. Accelerometer:

The accelerometer are placed at the bottom of the B pillar on rocker component as shown below.

Fig No. 28: Accelerometer

The below figure shows the graph of acceleration with respect to time. The acc1 means left side accelerometer and acc2 means right side accelerometer.

Fig No. 29: Graph Accelerometer.

In left side accelerometer the maximum acceleration is 10.07m/s. at t= 5ms and then it falls suddenly and goes on decreasing further. This jerk is caused by the impact of the car.

In right side accelerometer the maximum acceleration is 9.39m/s. at t= 2.5ms and then it falls suddenly. At time t= 15ms there is rise in acceleration to 7m/s. It is observed that there are more jerks observed on right side compare to left one due bending of front components and self impacting of the component due to bending. And then acceleration falls suddenly and goes on decreasing further.

3. Intrusion:

To observe the effect of impact at pedals there are two nodes selected at pedals. The nodes 66695 and 66244 with reference of node id 121739 and 122048 respectively are connected with a spring element with 1e-8kN/mm stiffness. As shown below.

Fig No. 30: Intrusion.

The below figure shows the graph of maximum displacement with respect to time.

Fig No. 31: Graph maximum displacement.

This are the springs with very low stiffness just to observe the displacement near the pedals. The first spring shows the maximum displacement of 180.79mm second spring shows the maximum displacement of 154.55mm which are within limit. which also means that there is no severe damage to the legs.

Conclusion:

1. It doesn't show actual simulation. Since engine components and other components are missing which absorb the maximum forces.
2. The maximum forces are developed in the rail component and least in hinge pillar.
3. The forces generated in component from maximum to minimum as rail component, Fender, shotgun, A pillar and hinge pillar.
4. From accelerometer it is clear that there are more jerks on right side compare to the left side.
5. The intrusion at pedal is within safe limit.