Aim: To carry out side crash simulation & study the analysis results of the BIW model of a generic car.

Objective:

1. Create necessary contact interfaces with recommended parameters
2. Remove penetrations & intersections if any
3. Rigid wall creation
4. Applying Kinematic conditions
5. Check model for good quality
6. Request cross sectional forces at cross members

Abstract

This project covers the various critical result discussion obtained from the simulation of side crash of vehicles. The model used in this project is a surrogated model to keep the number of nodes and elements within the limits of the student version of HyperWorks. Creation of interfaces and kinematic conditions has been done strictly based on recommended parameters for crash applications.

Workflow

Case Set-up & Execution

Unit Check

(can be seen in 0000.rad file)

The unit system thus followed from hereon in [Kg, mm, ms]

Model Provided

Contact Interface Card

The already present contact interface cards are deleted, a new contact interface card has been defined. We have selected Type 7 Contact in which the whole BIW model acts as both- slave and master.

The Recommended Type 7 parameters for crash applications are as follows:

1. I_stf= 4: Set stiffness of interface based on the softer of the master & slave.
2. I_gap= 2: Set variable gap to consider the true distance between parts.
3. I_del= 2: Remove slave nodes from contact because of element deletion
4. St_min= 1kN/mm: Specify minimum stiffness in the contact to avoid too soft contact.
5. Fric= 0.2
6. Gap_min= 0.5: Specify minimum thickness of the model to avoid numerical issue. Typically half of the thinnest part.
7. Inacti= 6: Remove initial penetrations where possible. Elsewhere, reduce to less than 30% of the defined gap value and adjust the gap with Inacti.
8. I_form= 2: Sliding forces are computed using stiffness parameters of interface. Usually results in bigger time-step.

Rigid Wall creation

For the side crash analysis we are using a cylindrical rigid wall, refer the following rigid wall card.

Intersection & penetrations check

(This check is performed in HyperCrash)

It can be seen from the Quality Browser Tab above that the penetrations & intersections in the provided BIW model is ZERO.

ENG_RUN Card

Under this card, the simulation time is set to be equal to 80ms

ENG_ANIM_DT Card

T_freq= 5.0, which implies we have taken up 16 animation steps (=80/5.0). T_freq has been taken to be a higher number so that the RADIOSS block for the simulation completes its job in less time as compared to the long time it will take if animation steps were requested at each and every second where T_freq=1.

Initial Velocity Set-up

(Solver Browser>> Create>>Boundary Conditions>>INIVEL)

Required velocity= 35mph= 15.6464mm/ms (to be specified in global Y-direction)

A new grnd_ID has been created and under nodal entities all the nodes of the BIW model has been selected, the selection is marked by the color white as follows:

Model Mass, Cog aspects

(Tools>>Mass details>>Mass, Cog, Inertia)

Current mass= 166.307 Kg

Target mass to achieve= 700 Kg

Mass to be added= 533.692 Kg

The initial Cog coordinates are:

X= 2420.6088

Y= 248.4562

Z= 588.9372

The initial Cog position can also be seen in the following graphic:

Type 1 mass addition was used to distribute the remaining mass equally among the node group. The node selection for mass addition can be seen in the following graphic:

Total number of nodes in the node group= 583

The new Cog coordinates are:

X= 2251.423

Y= 6.558

Z= 326.761

The positioning can be seen in the following graphic:

The mass summary is as follows:

It is seen that the target mass has been reached i.e. 700Kg(approximately)

Creation of Cross-sections

(Solver>>SECT>>SECT)

The cross-sectional forces are to be studied on the MID rail and the driver seat rail.

Mid Rail cross-section

Driver seat rail cross-section

Intrusion study points

Intrusions tell us how much the components from the crumple zone come inside the occupant safety. Any components from the engine, railings coming into the occupant area will lead to fatal injuries. That is why study of intrusion is important.

The intrusion points under study are:

1. Intrusion at end of B pillar
2. Intrusion at hinge pillar
3. Intrusion of the fuel tank region

For measuring the initial intrusions nodes on the opposite side of the above selected nodes are selected and a moving skew is created over there & assigned accordingly under the I_skew parameter of the TH/NODE definition card.

Intrusion point(End of B pillar)

Initial intrusion = 1307.647mm

Intrusion point at Hinge pillar

Initial Intrusion= 1312.854mm

Intrusion point of fuel tank area

Initial intrusion= 1310.469mm

Model Check

(Tools>>Model Checker>>RADIOSS Block)

This was done in Hypermesh itself, to check for the model errors.

No errors were found during the Model checker run. This is a green signal to proceed for the simulation.

Simulation

Energy and mass error checks

Energy error= -6.9% which is within acceptable limits of -15%. Negative energy error indicated that the energy has been dissipated which could be an indicator of elements overlapping on each other, releasing contact energy.

Mass error %= 0.01113x100= 1.113% which is between 1-3%, hence acceptable.

Simulation time= 79.90ms

Elapsed time= 2168.52 s

No. of cycles= 80001

Simulation Graphics

Result contours

Displacement contour

Von-Mises contour

Mass contour

Energy plots

Internal, Kinetic energy, Total energy

The internal energy increases gradually as the material absorbs the shock wave intensity. The kinetic energy decreases as the crash attains completion. The internal energy and kinetic energy curves can be seen to cross each other at 68^th ms. This may be due to the energy error that occurred while running the simulation.

Maximum internal energy= 52500 Kg*mm2/ms2 (approx.)

Maximum Kinetic energy= 85000 Kg*mm2/ms2 (approx.)

Total energy at end of simulation= 78500 Kg*mm2/ms2(approx.)

Hourglass, contact energy

It is recommended that {(Contact energy + Hourglass energy)/(Total energy)}x 100 < 15%...........expression(1)

Contact energy at end of simulation= 5000 Kg*mm2/ms2

Hourglass energy at end of simulation= 60 Kg*mm2/ms2

Expression(1) evaluates to 6.44% which is less than 15%. Hence, acceptable.

Mass

Model mass increases over time from 700Kg at t=0 to around 707.8Kg at t=80ms. This is because the solver has put some mass on the nodes to avoid time-step failure.

Cross-sectional forces

Mid Rail cross member

Max force on Mid rail cross section= 27.5kN around 60^th ms after which it decreases and increases(i.e. undergoes a lot of jerks) and attains a final value of 15kN at 80^th ms.

Seat Rail cross member

Max force on Seat Rail cross section= 2.625kN around 37^th ms after which the curve undergoes less jerks as compared to the mid rail cross-sectional force and attains a final value of 1.5kN at 80^th ms.

Intrusion Plots

Intrusion of End point of B Pillar

Max Intrusion obtained after simulation= 300mm

The point on the end of pillar B intrudes by a distance of= Initial intrusion – final intrusion= 1307.647mm-300mm= 1007.647mm.

Intrusion of Hinge Pillar point

Max Intrusion obtained after simulation= 600mm

The Hinge pillar point intrudes by = 1312.854mm-600mm= 712.854mm

Intrusion of Fuel Tank

Max Intrusion obtained after simulation= 250mm

The Fuel Tank point intrudes by= 1310.469mm-250mm= 1060.469mm which is extremely high and may cause serious accidents evidently. To reduce the intrusions around the fuel tank area, stiffer material can be used. Also, cross beams covering the fuel tank region would probably reduce the intrusions.

Peak Velocity of Node (on the inner side of door)

Peak Velocity= 16.5 mm/ms (approx.)

The velocity is maximum during the 5^th ms i.e. around the onset of crash and decreases as the crashing car comes to rest with jerks in between.

Conclusion

Side crash analysis simulation was performed successfully using the required parameters. Various results, energy plots and cross-sectional forces were studied to analyze how particular component behaves during a crash scenario.