ROOF CRUSH ANALYSIS OF DODGE NEON BIW AS PER THE FMVSS 216A STANDARD

OBJECTIVE:

The main of this project is to perform the roof crush analysis of Dodge Neon BIW as per the requirements and procedures in FMVSS-216a standard published in 2009.

FMVSS-216a STANDARD:

1. FMVSS 216, Roof Crush Resistance, establishes strength requirements for the passenger compartment roof of passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR (gross vehicle weight rate) of 2722 kilograms or less. The purpose of the standard is to reduce deaths and injuries due to the crushing of the roof into the passenger compartment in rollover accidents.
2. The prescribed Quasi-static loading device is a rigid unyielding rectangular block 762 millimeters by 1,829 millimeters. It shall not move more than 127 millimeters to achieve the specified resistive load when applied to the forward edge of a vehicle’s roof.
3. The resistive load to be achieved is 3 times the unloaded vehicle weight (UVW) of the test vehicle.
4. The Quasi-static loading device must be located as shown in the picture below,
5. 

PROCESS:

1. Based on the license limit up to 100K elements in Radioss, imported the neon's BIW reduced model, in order to reduce the computation time and also since the Quasi-static process is time-consuming.

2. Imported the Quasi-static impactor in the Hypercrash GUI and located the impactor-based on the FMVSS-216a standard as shown below,

3. Created the type 7 contact interface between the impactor as master and car as slave and self impact interface where the model serves as both master and slave with the recommended parameters as shown below,

• The contact interface between the impactor and the car helps in calculating the roof crush resistance when the force applied on the roof of the car.

4. Created kinematic conditions as follows,

• In order to compensate for the absence of wheels and shock absorbs, created rigid bodies as shown below,
• Created boundary conditions in the master node of the rigid bodies in order to lock the suspension shock tower translation in the z-direction as shown below,
• Created boundary condition with zero degrees of freedom in order to restraint the side body of the car. 
• 
• The impactor assembly contains a spring attached for stability, Created a BCS collector to fix the free end of the spring as shown below, this spring helps in measuring the displacement of the impactor.
• 
• Created a local coordinate system moving SKEW to define the direction normal to the impactor’s face and created a BCS collector to guide the master node of the impactor rigid body so that it is free to translate normally to the face of the impactor, but is fixed in all other DOFs.
•  Created an imposed displacement on the impactor's rigid body master node with time function as 0 mm at 0 ms to 200 mm at 200 ms, so that abrupt change in the acceleration of the impactor is avoided.
• 
• Function graph which defines the imposed displacement.
• 

5. Checked for the presence of flying parts in the model using quality--> check the connectivity of tree selection option in Hypercrash as shown below and connected them by using rigid bodies.

6. Checked for the penetrations and intersections in the model and cleared using the tools-->penetration checker option in Hypermesh.

7. Created control cards as follows,

• /ANALY-Defines the type of analysis and sets analysis flags.
• 
• The parallel arithmetic flag is set ON, the same numerical results will be obtained irrespective of the number of processors used. 
• If Subcycling option-2 is selected then in Radioss Starter Input file is only necessary in order for the Radioss Starter to allocate additional memory, here option 1 is selected so no additional memory created.
• /DEF_SHELL- This keyword is used to set default values for certain parameters in all shell properties, but options could still be changed in each property set input.
• 
• /DEF_SOLID- This keyword is used to set default values for certain parameters in all solid properties and thick shells. The default values defined here will be overwritten by any values entered on the individual property input.
• 
• /IOFLAG- Describes the input-output flags.
• 
• IPRI- Starter output printout flag, parts mass, inertia, rigid wall, interface, BCS, nodal masses, initial velocities details are printed.
• IOUTP- Output a STY model file flag.
• OUTYY- STY file output format flag.
• IROOTYY- STY file name flag.
• Idrot- Force computation of rotational DOF flag.
• /SPMD- Sets SPMD parameters for Hybrid Massively Parallel Program (HMPP) computation.
• 
• DOMDEC- Type of domain decomposition for SPMD version
• Nspmd- The number of SPMD domains.
• Dkword- User-defined value for requested memory used by RSB Domain Decomposition. The default value is computed by Radioss Starter.
• Nthread- Number of SMP threads per SPMD domain.
• /TITLE- Describes the title.
• 
• The constant nodal time step, run time, animation output frequency, time history output frequency as follows,
• 

8. The required time history files and animation files are requested for post-processing the results.

9. Checked for any errors in the model using quality-->model checker in Hypercrash and also tools-->model checker in Hypermesh and rectified them by using autocorrect option and some are rectified manually, finally came up with three warnings that can be ignored if the simulation runs smoothly.

10. Using the Radioss solver, started the simulation run with the multithreading of 4 threads for the computation purpose. After the completion, the following checks are made,

• starter output file diagnostics:
• the total mass and inertia calculated by the starter conform to the expected value.
• the mass and center of gravity match the expected value as in the model.
• 
• errors, warnings calculated by the starter are none, is a good sign to move further.
•  
• engine output file diagnostics:
• the timestep, energy error, mass error are checked and observed that the values are within their limit.
• the message "Normal Termination" has been printed, which is a good sign for post-processing the results.
•  
• the time step value 0.0005 ms remains approximately equal to the minimum value (ref graph below).
• the energy error ranges from 0% to -11.7%, is within the limit -15% to +15% , which is acceptable.
• the mass error value is 0.021% < 1% , is also acceptable.

OUTPUT:

1. Force vs Displacement plot:

• 
• As mentioned in the FMVSS 216a standard, the impactor shall not move more than 127 mm to attain the roof crush resistance load of 3*UVW, but here the impactor is made up to 200 mm. But the roof crush resistance load at 127 mm is extracted as shown in the plot above.
• The total weight of the reduced model is 174.8 kg, so 3*174.8*9.81=5144.364 N, and the roof crush resistance load at 127 mm is 9.109 KN=9109 N.
• The resistance load 9109 N at 127 mm is above the 3*UVW, so the strength required for the passenger compartment roof of the passenger car is attained successfully as per the standard.

2. Animation output:

• Internal energy
• 
• the maximum value of internal energy is 0.244 J at node 100103 which is at the bottom of the A-pillar.
• plastic strain
• 
• the maximum value of plastic strain is 0.04709 at node 230183 which is at the center cross member of the roof.
• Mass variation due to mass scaling DT/NODA/CST
• 
• maximum mass variation of 1.766 kg occurs at node 391920 which is at the rear door.
• von mises stress
• 
• the maximum von mises stress is 0.2646 KN/mm2 at node 103580 which is at the A-pillar.
• Hourglass energy
• 
• the maximum hourglass energy is 1.812 J at node 346265 which is at the front door lock, this can be removed by using Isolid=24 (HEPH) element type which has physical stabilization hourglass control.

3. Energy balance:

• 
• since the process is a quasi-static process, there is no motion or in specific no velocity involved as in the dynamic analysis like the crash test. The only movement is the impactor displacement from 0 mm to 200 mm, so the kinetic energy reaches its maximum value up to 42.0141 J.
• whenever a body deforms some energy (internal energy) will be absorbed in it due to the straining effect and that straining effect can be caused due to the suddenly applied load or gradually applied load or load with an impact. In this case, the straining effect is caused due to the gradually applied load. so the internal energy reaches up to 1278.65 J.
• The contact energy reaches up to 174.705 J, which is the energy spent to resist the slave nodes not to enter the master element gap during the contact between the impactor and BIW.
• Hourglass energy reaches up to 0.534846 J due to the usage of Isolid=1(brick 8) element type which has a single integration point with viscous hourglass stabilization.
• The total translational energy reaches up to 1496.18 J due to the energy dissipation.
• According to the stability equation, TTE=IE+KE+RKE+HE+CE, the energies obtained are calculated as follows, 
  • IE= 1278.65 J + KE=42.0141 J + CE=174.705 J + RKE=0.273579 J + HE= 0.534846 J =1496.177525 J
  • so, the energy stability equation satisfies.
• the condition, hourglass energy + contact energy < 15% of total energy, is satisfied as follows,
•  
  • HE=0.534846 J + CE=174.705 J= 175.239846 J < 15%*1320.66=198.099 J

4. Mass balance:

• 
• from the above graph, it is obvious that the mass addition is very minute and the variation is 0.021% < 1%. This happens due to the usage of /NODA/CST.

5. Time step:

• 
• Here the time step that remains varying above the specified minimum value.

ANIMATION:

RESULT:

• The roof crush analysis has been done as per the procedures and requirements of the FMVSS 216a standard.
• The force vs displacement graph has been plotted and met the requirement of roof crush resistance=3*UVW.
• The energy vs time curve graph has been plotted and the required results are obtained.