Roof Crush Analysis on Dodge Neon BIW- Using HyperMesh RADIOSS

Objective: To Perform Roof Crush Analysis On Dodge Neon BIW Using Test Protocols Of FMVSS 216 Standards.

Introduction :

Roof crush simulation Federal Motor Vehicle Safety Standard No. 216 (FMVSS 216) first published in 1971 specified the test requirements and configurations of Roof crush process. The roof strength is measured by the resistance force required to push a rigid plate into the roof structures. According to the latest version of FMVSS 216, the reaction force (RF) is increased from 1.5 times of unloaded vehicle weight to 3 times. The test plate locates with roll angle 25 and pitch angle 5. The initial contact point is on the longitudinal centreline of the lower surface of the test device, 254 mm from the forward-most point of that centreline. Then the test device is applied to move in the downward direction perpendicular to the lower surface.

The Test configurations of the regulation.

In the following simulation, Imposed Displacement is defined in the roof crush simulation. The unloaded weight of the original vehicle is 1767 kg. According to the newly updated regulation FMVSS 216, the resistance force should be larger than 51.95 kN, 3 times the unloaded weight.

Full Model Setup

Simulation is a quasi-static process which is time-consuming. In order to reduce the computation time, the Full car model is been reduced so the name of nodes elements are reduced and Advanced Mass Scaling is used since the simulation is a quasi-static process to reduce the computation time.

Reduce model

The Test Plate is been aligned as per the Standard Regulation.

The test plate locates with roll angle 25° and pitch angle 5°

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 ( -3500.00, 584.822, 1343.06)

Unit System used throughout the simulation is Length (mm), Time(ms),Mass(Kg),Force(KN), Pressure(Gpa),Velocity(mm/ms),Density(M Kg/L),Energy(J)

Model Setup

Contact Interface

Two contact interface is created Self-Contact for the car model and Contact between the Test plate and the car model

• Self-Contact for the Car model (Type 7 )

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 a element is deleted, the corresponding segment is removed from the master side of the interface

Fric(coefficient of friction ): 0.2

• Contact Between Test Plate and Car Model (Type 7)

Master: Test Plate

Slave: Car Model (Selective nodes)

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 a element is deleted, the corresponding segment is removed from the master side of the interface

Fric(coefficient of friction): 0.2

Penetration Check

Once the contact is defined we have to make sure there is no initial penetration and Intersection

Connectivity Check

We have to make sure all parts are connected and there is no free floating part, if so that part alone will move separately in their own degree of freedom during the simulation

Floating part are connected using spring 2N element and P13_SPR _BEAM Properties is created for the spring element

Load Collectors

Local MOV Skew is created on the test place such as z axis is perpendicular to the test plate

Boundary Conditions

• Suspension Shock Tower

BCs is created for all the Suspension Shock tower Transitional along z axis is locked Since the Wheel will be attached to the suspension shock tower the transitional along Global z-axis is locked.

• Test Plate Rigid Body

BCs is created for the Rigid body in Test plate 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 test plate 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

Function Curve

0s = 0mm

200s = 200mm

Control Cards

• /ANALY card (Defines the type of analysis and sets analysis flags.)

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]

• /DEF_SOLID card

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 file flag): -1 - Do not output STY model file

OUTYY(STY file output format flag) : 2 Format 44

IROOTYY(STY file name flag) : 0-Ynnn writing file format is RunnameYnnn (old format

IDROT(Force computation of rotational DOF flag): 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
• The constant nodal time step is Used With T_scale : 0.67 and T_min:0.001
• Print time history for every 0.0001 seconds
• Animation file is created for every 0.005 seconds

.Out-File:

Number of Cycle	ELAPSED TIME	Energy Error	Mass Error
199554	5918.70 s	-12.1%	0.4536E-01

The energy error is 12% which is acceptable and mass error gradually increases but didn't exceed more than 5%, So the Result is acceptable for this Simulation.

Results:

Displacement

Max Displacement : 238mm

Von Mises Stress

Max Stress : 0.302 Gpa

Plastic Strain

Max Plastic Strain:0.1877

Specific Energy

Graphs:

Energy graph

Since we have given imposed displacement to test plate the kinetic energy starts at the starting of simulation, but at 65ms only the test plate touches the roof and deformation starts which makes the kinematic energy slowly increases at reach max at 200ms as 91J.

As a general rule, to determine whether an analysis is quasi-static, the kinetic energy of the deforming structure should not exceed a small fraction (typically 5%) of its
internal energy throughout most of the simulation

The internal energy in this simulation increases exponentially once the deformation starts at 65 ms and reaches max 410J at 200ms.

The total energy should be equal to the external work done but this is simulation there is a slight loss in total energy that’s because of contact energy.

Contact and Hourglass Energy

Contact energy starts at 65ms (i.e when the Test plate and car come to the contact) after 65ms the contact energy gradually increases and reached max 70J at 200ms because of this energy only there is a slight loss in total energy in the simulation. the Hourglass energy is 0.030 which is negligible in this case.

TH Node (101929)

To measure the displacement of the Roof Rail in the car TH Node output block is used for one node 101929 in the roof rail with a local skew of the test plate to find the displacement along the local Z-axis

The node has displaced 140mm in the local z-axis since there is clear deformation in the Roof Rail This might injure the occupant but The severity of injure is depended on the height of the occupant.

Resistance Force

Normal force along the z-axis of Test Plate – Car Interface force will determine the Resistance force

Force vs Displacement

Maximum Resistance Force is 5.5KN at 140ms of Node 101929

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.

The full car model having the weight of 1216.55kg i.e 3*1216.55*9.8 = 35.8KN still the target load is way below the standards

The target load 47000N (3*GVM) is not matched.

To match the standards Target load if the UVM is Taken to be 1600 as it is under FMVSS standard with vehicles with 2722kg or less so it is acceptable and GVM is calculated and reaches the target load.

Conclusion

The Roof crash analysis is done on the surrogate model of neon Dodge due to limitations with the student version of the Hyperworks. The improper meshing leads to some errors which are in an acceptable range.

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.

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.

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.

The Different approach to Improve Roof crush Resistance

• 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.
• Material Approach: Use of Composite Body Solutions (CBS) such as Foams, Plastics, Alloys, and non-ferrous metals. CBS Materials like Foam have a high 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.
• The A-Pillar, Center Pillar Assembly, Doors and rear side members have to be reinforced thereby building better structural integrity.

File: https://drive.google.com/file/d/1tGgVYrL8X_bEMXTS3YVn1fx_frbWlnUG/view?usp=sharing