PERFORMING ROOF CRASH ANALYSIS OF A CAR WITH THE HELP OF IMPACTOR

OBJECTIVES

1. To understand the different Kinematic Conditions.
2. To understand the different Loading Conditions.
3. To assign recommended contact interfaces parameters for crash analysis.
4. To understand the Time step Control for crash analysis.
5. To learn about the Output Requests for post processing.
6. To learn about the Check Debug for post processing

7. To plot the different contours formed with use of various contact interfaces and parameter change.

Check with the unit system, either use [Mg mm s] or [kg mm ms]

• This can be done using the starter _le neon_front_0000.rad in notepad as shown below.

• Import the file neon_roof_0000.rad
• Import the file FMVSS_216_ROOF_IMPACTOR_coarse_0000

1. Car
2. Impactor

• It will appear in wireframe mode.
• Click on shaded mesh to view the surfaces in shaded form.

Transformation

• This will require (in order)
• A 180° rotation about the global z-axis
• A 5° rotation about the axis through axis AB
• A 25° rotation about the axis through axis AC
• A translation to put point A at global ( -2145.26, 584.822, 1343.06)

Create an appropriate interface, friction 0.2 and recommended parameters.

• Two contact interfaces is created Self-Contact for the car model and Contact between the Impactor and the car model
• There are different contact interfaces are present for each part. But it is good to have lower number of interfaces so that we will get faster simulation.
• Delete the available interfaces in the original model, and create a new one with the Type 7 interface.
• Recommended properties as follows

• Igap (Determines how the size of the gap is calculated): 3 Variable gap + gap scale correction of the computed gap + size of the mesh is taken into account to
• Avoid initial penetrations during self-contact.
• Fscale_gap(Gap scale factor) : 0.8
• Gapmin(Minimum gap for activation of the interface ): 0.5
• Inacti(Action to take if initial penetrations exist): 6 Gap is variable with time but initial penetration is computed
• Istf(Affects how the stiffness of the interface is calculated): 4 Kmin=(Km, Ks)
• Iform(Friction formulation): 2 Stiffness
• Stmin(Minimum stiffness to use in the interface): 1
• Idel(What to do with slave nodes and master segments if an element fails (deleted) that they are attached to): 2 when an element is deleted, the corresponding segment is removed from the master side of the interface
• Fric(coefficient of friction ): 0.2

Contact between the Impactor and the car model

• Master: Impactor
• Slave: Car Model (Selective nodes)

Make sure of no penetrations and intersections

• To run the analysis, we should make sure that there is no intersection and penetrations between two bodies of parts
• To check for penetrations and intersections in a hypermesh.

• As there are no penetrations and intersections available in a model. We can run the analysis. If the quality check shows any intersection or penetration we can fix it by using an auto fix tool.
• If the auto-fix is failed to clear the penetrations or intersections then we have to correct as per the manual method.

Calling Interfaces to Time History files

Creating Rigid Body as a suspension

• As the reduced model don’t have the suspension assembly. We have to create the rigid body (RBODY) and constraint the motion using BCS. This will resemble the suspension system.
• We have to use local moving SKEW to define the coordinate system locally as the global system is not suitable to use for small components.
• Similarly BC’s are created for car rigid body, spring, and Impactor rigid respectively.

Application of Gravity Load to whole model and constrain the motion of suspension in global Z Axis

• Defining the gravity function to apply the gravity load to the whole model. As the gravity is all the time constant , we can define the function as follows.

• Gravity is applied on negative global Z axis so use scale factor as -1.
• Select the nodes of whole car to apply the gravity load.

Impactor Boundary Conditions and Skew for Impactor

• The impactor assembly contains the a spring attached for stability.
• As the spring is free. We have to constrain it motion in all direction.
• The impactor skew is already defined as z axis is perpendicular to impactor plate.

• The impactor skew is already defined as z axis is perpendicular to impactor plate.
• The impactor boundary condition is allowed in local z direction. As the skew is defined for impactor.

Apply the BCS to Impactor plate so that we will contrain the motion of impactor

• BCs is created for the Rigid body in impactor and all degree of freedom is locked expect local z-axis along the axis of Displacement and the free end of spring in the master node of a rigid body in test plate, all the degree of freedom is been locked for the spring.

Imposed displacement

• Imposed displacement is added to the master node of a rigid body in impactor in direction of Local Z-axis Function curved is created for displacement which changes with respect to time to avoid abrupt change is the acceleration of test plate
• We have to apply imposed displacement for impactor as follows
• Impose the velocity of the impactor starting from 0 mm/s at t = 0. The displacement of the impactor should be 200 mm @ 200 ms.
• Hence we need to create the function as input for imposed displacement.

Setting up the Control Cards

• Iparith = 1 Parallel arithmetic option is ON.
• The Parallel arithmetic flag is set ON, the same numerical results will be obtained irrespective of the number of processors used. This result is not guaranteed in case of incompatible kinematic conditions in the model

• /DEF_SHELL card, ( 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 and in this case, the latter will prevail.)
• ISHELL : 4-Q4 with improved type 1 formulation (orthogonalization for warped elements)
• Ismstr : 2-(default) Full geometric nonlinearities with possible small strain formulation activation in Radioss Engine
• Ithick : 1-Thickness change is taken into account.
• Iplas : 0-Default if /IMPLICIT is not used in deck. Radial return
• Istrain : 2-No
• Ish3n : 1-Standard triangle (C0)
• Idrill : 0-Default if /IMPLICIT is not used in deck [No]

• ISOLID : Standard 8-node solid element, one integration point. Viscous hourglass formulation with orthogonal and rigid deformation modes compensation (Belytschko).
• Ismstr : Full geometric nonlinearities (/DT/BRICK/CST has no effect).
• I_strain : No

/IOFLAG card Describes the input-output flags.

• IPRI(Starter output printout flag) : 2 - 1 + boundary conditions + nodal masses + initial velocities
• IOUTP Output a STY model flle flag): -1 - Do not output STY model 􀂦le
• OUTYY(STY flle output format flag) : 2 Format 44
• IROOTYY(STY file name flag) : 0-Ynnn writing 􀂦le format is RunnameYnnn (old format
• IDROT(Force computation of rotational DOF 􀂧ag): 0-Rotational DOF not always calculated

/SPMD card - Sets SPMD parameters for Hybrid Massively Parallel Program (HMPP) computation

• DOMDEC (Type of domain decomposition for SPMD version) : 3 Multilevel Kway decomposition.
• Nspmd (Number of SPMD domains): 4

• Termination Time: 200ms
• Print time history for every 1ms
• Time frequency = 5

• Run for 200ms and the frequency of the animation _le is set to 5. So, by this we get 40 animation _les for the run time of 200ms. So that the result is more accurate.
• The Output Blocks (Hypermesh) or Data History (Hypercrash) for contact interfaces, parts, and rigid bodies are created.

Use model checker to ensure good quality.

• Before going to the actual run we should ensure the quality of the model.
• In Hypermesh go to Tool> Model checker> Radioss Block > Then the system will show the error and warning. Try to find out the error and correct then or use the autocorrect tool.

• In Hypercrash go to Quality> Model checker> Run. Then the system will show the error and warning. Try to find out the error and correct then or use the autocorrect tool.
• Before running the simulation is better to do the model checker and make sure there is no error in the simulation

Output request

• Results and Post-processing-
• After the run completion, we need to check the roof Crash_0001.out.

Debugging

• For debugging we have to see the roof Crash_0001.out file

The Energy Error computed by RADIOSS is a percentage.

• If the error is negative, it means that some energy has been dissipated.
• Negative Energy Error since it is not counted in the energy balance. The normal amount of Hourglass energy is about 10% to15%.
• If the error is positive, there is an energy creation. In case of using QEPH shell formulation or fully integrated elements, the Energy
• Error can be slightly positive since there is no Hourglass energy and the computation is much more accurate. An error of 1% or 2% will be acceptable.

The Mass error is 0. 0.45E-01 Kg which is acceptable as no change is happened to mass.

The Simulation time for frontal crash is much more.

• Action to take if initial penetration. Removal of initial penetration where possible. Elsewhere, reduce to less than 30% of defined gap value and adjust the gap by using in Inacti.
• When we are not using no failure criteria simulation time required is quite less as compared to others.

As per the above image, the energy error is -12.8% and mass error is 0.45-01. So we can go for results as the values are in an acceptable range.

• Max Stress: 0.1785GPa

• Displacement: 235.7mm

• Plastic Strain: 0.062.72mm

• Specific Energy:116.2J

All Energies

Interfaces of Car body and Imapctor and Car body

The resultant force on different suspension

• According to FMVSS 216 Specified strength to weight ratio required a resistance force of 3 times GVW(Gross Vehicle Weight) to Protect the Passengers from the roof crash, the current weight of the model is 174.8 Kg Resistance force required is 3*174.8*9.81 = 5144.364. Since the Maximum Resistance force from the plot is greater than the required force.
• GVM is calculated and reaches the target load.

CONCLUSION:

1. The position of the Center of Gravity of a vehicle is vital in the crashworthiness, so maintaining the weight balancing of a vehicle is the skill of design engineer.
2. As we are using the half model and with added masses, if we can go for full vehicle body analysis then more realistic results can be obtained.
3. The improper meshing leads to some errors which are in an acceptable range.
4. And we also plot the force vs. displacement plot of the Impactor which is needed according to the FMVSS standard. The roof resistance produced while the impactor crushes the roof should be greater than the 3 times the unloaded weight of the car. But with the current mass, it can't meet the Target load as specified by the FMVSS standard.
5. 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 of 2722 kilograms or less.
6. The Different approach to Improve Roof crush Resistance
7. Geometric Approach: Increase the thickness of Roof, Roof Rail, Panel B-pillar inner rail, Side Panel, Inner Rocker panel, Floor channel, Front floor, Rear Floor, and Trunk Floor.
8. Material Approach: Use of Composite Body Solutions (CBS) such as Foams, Plastics, Alloys, and non-ferrous metals. CBS Materials like Foam have a high
9. Strength to Weight Ratio which increases the Force absorption capacity of the structure hence the roof is able to withstand higher forces for a given deformation. The material approach is preferred over the Geometric approach due to space constraints in the passenger compartment as well as weight limitations.
10. The A-Pillar, Center Pillar Assembly, Doors and rear side members have to be reinforced thereby building better structural integrity.

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https://drive.google.com/file/d/1DA-hjPd0rqu3U8cHHzoMkzJnIqCXB5fT/view?usp=sharing