FMVSS 216 Roof Crush Test

 

FMVSS 216 Roof Crush Test

Objective:

The objective of this project is to simulate the FMVSS 216 Roof Crush Test and determine whether the given BIW frame is in compliance with FMVSS 216 Guidelines.

Case Setup and Model Setup:

1. First, the BIW model is imported in hypercrash.

2. Then, the FMVSS impactor is imported and merge option is selected to merge the two models.

3. The system default offset is applied so that there are no ID or other conflicts between the Impactor model and the Car model

4. The required transformation operations are carried out by using the option RADIOSS Tools -> Transformation, to position the FMVSS impactor over the car model according to the FMVSS 216 Testing Standards.

Testing position according to standards:

Model after transformation:

5. The model checker is then run and the errors and warnings are then checked to find any unassigned properties or materials for the components.

6. The errors in the given model are depicted in the picture below

7.The error named Loose node of spring gets rectified when the free end of the spring is constrained.

8. Then, the connectivity of all the parts in the load path is checked to make sure that there are no free parts as it might lead to incorrect results.

9. Since there are some free parts, they are connected using springs.

10. Since there are no unassigned materials or properties, the thickness intersection is checked and if any intersections are present, they are removed by manipulating the nodes

11. After these preliminary operations are done, the interfaces, boundary conditions and load case are set up.

 

Interfaces:

1. Global Self Contact:

1. A global contact interface is used here to take into account self-contact or penetration of the BIW parts during the application of force by the impactor.

2. Hence a multi-purpose contact (TYPE7) is defined in the model.

3. In the contact interface tab, a new contact interface is created, by selecting surface of all parts as master surface and selecting all the nodes in parts as slaves.

4. This establishes a self-impact interface which takes into account the penetration of components in the model.

5. The optimum parameters for type 7 are then set.

 

2. Impactor – Car Contact:

1. To measure the reaction force or resistive force generated by the car when the force is applied using impactor, a new separate interface is required.

2. A new contact interface is created between the impactor and car by choosing impactor’s surface as the master surface and the car’s surface as the slave surface.

3. The optimum parameters for type 7 are then set.

 

Boundary Conditions:

1. Rigid body:

1. Since a reduced model is used to save computation time and load, some of the parts in the right side of the car are removed and represented in the form of a rigid body as shown in the picture.

2. A boundary condition is imposed on the master node of the rigid body to constrain translation and rotation along all the axes.

 

2. Shock tower:

1. According to the test standards, the car is supported on a sturdy platform when the impactor moves and applies the load.

2. As there are no wheels in the car due to the testing requirements and there is no possibility of the car’s suspension system to move the car up or down during the test, the shock towers are constrained in the model such that there is no translation and rotation about the Z – Axis.

 

3. Impactor:

1. The impactor is tilted at an angle in the model and hence a local coordinate system is required to move the impactor in the direction normal to the face of the impactor

2. A moving skew is created to define the local coordinate system and the master node of the impactor rigid body is constrained to make sure that the impactor is free to move normal to the face of the impactor.

 

4. Spring:

1. A spring is present in the impactor assembly for stability and to measure the displacement of the impactor which will be used later during post processing.

2. The free end of this spring in the impactor is constrained in such a way that translation and rotation along all the axes are restricted.

 

Setting up Load case: The unit system followed is kN, kg, mm, ms.

1. Gravity (GRAV)

1. Gravity is applied to all the nodes in the model

2. To apply gravity, a function/graph is first defined.

3. In this model, as the gravity is acting in -Z direction, the direction in translation option is set to Z.

4. To make sure that the gravity is acting in the -Z direction, either the Y- Scale factor is set to -1 or while defining the graph, Y value is entered as -0.00981.

5. The yellow arrow in the model indicates the direction of the gravitational load.

 

2. Imposed displacement:

1. A displacement of 200 mm is imposed on the impactor by defining a function/graph.

2. The skew created for defining the normal to the Impactor is used to define the direction of the displacement of the impactor.

3. The arrow indicates the direction of application of the defined imposed displacement.

 

Output requests:

1. Data History:

1. Data history is used to record some very important physical quantities like force, displacement etc. The physical quantities are recorded along with the simulation time and saved in T01 file.

2. This file can be used in hypergraph to generate different plots to better understand the simulation.

3. Radioss usually saves the global variables like Internal energy, Kinetic energy, hourglass energy, contact energy, etc by default.

4. Other quantities like forces can only be saved if data history is requested for the specific type of force or moment or work.

5. Data history for the impactor is needed to record the resultant force.

6. Go to Time history, add new TH of Interface, choose the impactor- car interface and select the physical quantities to be recorded(Output variables) which in this case is, total resultant force

7. But here, the output variable is set to default which saves all the default physical quantities.

8. Any additional TH for parts, rigid bodies, springs etc can also be requested if needed.

 

2. Animations:

1. Animations are also created to visually assess the deformation, mass addition, stress, strain, etc

2. To request animation, in the control cards tab, under engine keywords, toggle ANIM_DT and set the time interval to 5ms.

3. Next, the required animations like elemental energy, elemental equivalent plastic strain, Elemental Von Mises Stress, Elemental Hourglass energy and nodal added mass are requested in the same way.

4. Another method to request animation is to edit the _0001.rad after the model is exported.

5. As the software mainly uses keyword, the keywords for animation i.e. /ANIM, /ANIM/ELEM, etc. can also be used to request different types of animations for different element types

 

Observations/Findings:

1. Animation:

 

2. Energy Balance:

1. After the simulation is done, energy balance is checked by plotting internal energy, contact energy, hourglass energy, kinetic energy and total energy in a graph.

2. Since this is a quasi – static simulation, the energy balance graph will be different from that of a full dynamic impact simulation.

3. At t=0, the impactor starts moving towards the car and only after sometime, it makes contact with the car.

4. The total energy starts at 0 Joules and gradually increases because unlike other impact scenarios, there is no initial velocity at the start of the simulation.

5. Hence, as the impactor starts deforming the car, the total energy and internal energy increases from 0 Joules and reaches the maximum value at the end of the simulation.

6. The contact energy is 6.6 % of the total energy, (hourglass energy + Contact energy)/ Total energy = 6.6 % which indicates the simulation results are valid and acceptable

7. The engine output file is also checked to make sure that the energy error and mass error are within acceptable limits

8. The energy error is -6.4 % which is within the acceptable limit of less than 15 % and mass error is 0.02 % which is within the acceptable limit of less than 2%

 

3. FMVSS 216 Simulation Validation:

1. The total resultant force is the resisting force generated by car frame when it is loaded.

2. According to the new FMVSS 216 standards, the resisting force generated by the car structure must be at least 2.5 times the Unloaded Vehicle Weight (UWV) of test vehicle when the test vehicle doesn’t weigh more than 2722 Kilograms.

Resisting force = 2.5* GWV

3. The ratio of the resisting force to the weight of the vehicle is also called Strength to Weight Ratio (SWR)

SWR = Resisting force / GWV

4. Generally, high SWR means the car is safer.

5 .The IIHS issued that the acceptable SWR is 3.25, marginal SWR is 2.5 and anything lower than that is poor.

6. Another criteria is that the peak value of resistance force must be attained preferably within 127 mm (5 inches) of the impactor displacement.

7. Even though the acceptable SWR is 2.5, the SWR need not necessarily be exactly 2.5. It can also be higher than 2.5 to improve the safety of the car.

8. In this case, the expected minimum resisting force is 47000 N and SWR value of 3 for the assumed weight of the car as 1566.66 Kgs.

Force Vs Displacement Plot:

9. From the graph, it can be found that the peak value of resisting force is 16.9 kN at 67 mm of impactor displacement.

10. The total resultant force is lesser than the minimum acceptable resistance of 47kN and obtained SWR is 1.09

11. Since the minimum acceptable resistance value is not reached and the SWR is less than 2.5, it can be established that the car’s frame does not comply with FMVSS 216 regulations.

 

Result:

FMVSS 216 Roof Crush Test was simulated to validate whether the given car frame complies with the standards.

Parameter	Expected according to requirement	Obtained
Total resultant force (or) resistance kN	47 or greater than 47	16.9
Strength to Weight Ratio (SWR)	3 or greater than 3	1.09

 

Learning outcome and Design Improvements:

1. Checking connectivity of parts is very vital as loss of connectivity between parts will definitely produce incorrect results.

2. From the Force Vs Displacement graph, it can be established that the given car frame does not comply with the FMVSS 216 standards.

3. The obtained strength to weight ratio may be less either due to usage of reduced model or lack of structural reinforcements in BIW frame 

4. There are two methods to increase the strength to weight ratio (SWR) of the BIW frame.

5. One method is to reduce the weight of the vehicle by using an optimized frame with less structural members and exotic lightweight materials without losing the strength of the frame.

6. Another method is to use a combination of high strength low weight alloys, polymers and composites to reinforce the A pillar, B pillar and roof side rails of the car’s BIW frame.

7. Of the two methods mentioned above, the most efficient method is chosen carefully to increase the strength to weight ratio (SWR) of the BIW frame.

Conclusion:

The given car was tested according to FMVSS 216 Roof Crush standards, strength of the car was studied and methods to increase the strength of the car’s frame were discussed to make the car comply with FMVSS 216 Regulations.