FEM Barriers For Crash-Development - HyperWorks: Open Architecture

FEM Barriers For Crash-Development:A New Modelling Approach

Bernhard Fellner (Magna Steyr), Bernd Fachbach (Mag na Steyr), Thomas Jost (vif), Thomas Heubrandtner (vif), Chris tian Ruff (vif)

Date: 30.08.2007 Author: Bernhard Fellner, R&D Crash & Safety 1

Abstract:Titel: FEM barriers for crash development – a new mo delling approachAuthor: Bernhard FellnerCo Authors: Thomas Jost, Thomas Heubrandtner, Christ ian Ruff, Bernd FachbachCompany: MAGNA STEYR Fahrzeugtechnik AG & Co KGKeywords: Design Optimisation / Safety

Abstract:Crash barriers with a defined stiffness and deforma tion behaviour are used to simulate the kinetic ene rgy and

energy absorption of a collision partner during an accident in vehicle safety development. Almost all actually used barriers are made of alumi nium honeycomb material in different layers and in different

stiffness. The deformation behaviour is made up by global and local effects like energy absorption, deformation and failure of the honeycomb, the glue and the covering blades. Behaviour strongly depends on the impacting structure and its surfaces.

A project of MAGNA STEYR together with our partners (VIF – The Virtual Vehicle Competence Centre / Dynamore / ESI) deals with the aim of an overall val idated numerical barrier model. High validation lab el on global and local deformation modes and effects as w ell as numerical stability and low computing costs are aimed. First focus has been laid on the IIHS side i mpact barrier. Benchmarks as well as several princi pal testing series have been carried out to analyse the regularity of global and local effects. Also many previously carried out full vehicle crashes from di fferent development projects have been analysed. Crashed barriers have been cut into sections to loo k at the local effects and their statistical behavi our. Various numerical studies have shown that the typic ally used solid elements are not any more accurate to local deformation behaviour. New modelling approach es have been tried, specifically a beam model shows significant improvement on reproduction of local de formation modes as well as global behaviour althoug h validation work is still going on.

When the work on the IIHS side impact barrier is fi nished the same modelling approach will be also used on the other barrier models used in safety dev elopment.


Contents:

• Motivation:– Vehicle Development General – Conventional Barrier Performance

• Barrier Model Concepts:– Honeycomb Behaviour– Different Approaches for a Barrier Model – Testing / Validation

• Conclusion• Acknowledgements• References


Motivation:• Motivation:

– Shorter development time– No prototypes, testing in pre-series

Demand:– Good prediction of structural behaviour– Good prediction of biomechanical behaviour– Confidence in simulation results

Problems in Subsystems/Components:– Material models (incl. Failure)– Joining techniques– Boundary Conditions (Barriers)– …

There are numerous Tests performed with deformable honeycomb barriers:

– Frontal Impact: EuroNCAP, IIHS, …– Side Impact: EuroNCAP, SINCAP, IIHS, …– Rear Impact: FMVSS301

productionconcept serial development SOP productionconcept serial development SOP productionconcept serial development SOP

Definition ofcosts per unitDefinition ofcosts per unit

Increasing simulation effortsIncreasing simulation efforts

Reduction ofprototypesReduction ofprototypes

Co

sts

Time

Co

sts

Time

Frontloading drivendevelopment processFrontloading drivendevelopment process

Development based on hardware prototypesDevelopment based on hardware prototypes

System Level (vehicle)

Subsystem Level (airbags, trims,…)

Component Level (material models, joints,…)

System Level (vehicle)

Subsystem Level (airbags, trims,…)

Component Level (material models, joints,…)

System tests (sled, crash

test)

Subsystem tests (impactor

tests)

Component tests (material

tests)

System tests (sled, crash

test)

Subsystem tests (impactor

tests)

Component tests (material

tests)

Verificationof simulationVerification

of simulation

Leve

l of d

etai

l

Development Time

Leve

l of d

etai

l

Development Time

Verificationof complete

vehicle

Verification of components

Verificationof subsystems

Verificationof complete

vehicle

Verification of components

Verificationof subsystems

Simulation of complete vehicle

Simulation of subsystems

Simulation ofcomponents

Simulation of complete vehicle

Simulation of subsystems

Simulation ofcomponents

(1)

(1)


Motivation:

• Conventional Barrier Performance:– Unsatisfying Performance of conventional barrier models

made of solids:• Local and global deformation behaviour differs from reality• No local rupture

• This results in over- or underestimating vehicle deformations• Biomechanical simulations worthless without right structural behaviour

– Optimised barriers with empirical stiffness distribution:• Not physical• Not general valid (e.g.: SUV / Sports car)

Benchmark model against solid rocker Benchmark model against narrow beams Detail

(2)

Empirical optimised barrier


Barrier Model Concepts:

• Deformation Analysis:– Honeycomb material shows typical deformation

modes:• Crushing in localized bands at a constant load level

in T-Direction

• Sliding of the deformed bands in LW-Plane• Folding bands in LW-Direction• Local rupture at a low force level

T-Direction:

LW-Direction:

(3)

(4)



• Alternative Concepts:– Solids with Discrete Beams:– Shell Element Model:– Discrete Beam Model:

Dis. LW-Beam

Solids

Dis. L-Beam

Model with honeycomb style mesh, discrete beams to represent the L, and LW properties:

– Problems with local rupture– Cannot be used in full barrier model due to

failure criteria



• Alternative Concepts :– Solids with Discrete Beams:– Shell Element Model:– Discrete Beam Model:

Problems with Shell Element Model:– Strong dependency of reaction force

on shell size– CPU Time >>

– Result depends on software version

Crush Resistance in T-Direction:

TestV3_5/19mmV4_2.5/19mmV8_5/5mmV19_5/5mmDyna971

TestV3_5/19mmV4_2.5/19mmV8_5/5mmV19_5/5mmDyna971



• Alternative Concepts :– Solids with Discrete Beams:– Shell Element Model:– Discrete Beam Model:

Dis. T- Beams

Dis. LW-Beams

Dis. L-Beams

Model with discrete beams representing the properti es in the main directions:

– Modelling of characteristic deformation behaviour(localising of deformation, separation of deformed and and undeformed areas)

– Modelling of local crushing

– Macro Cells possible

– More detailed model with comparable CPU time

– Numerical stability

– Constant time step (2.5 E-6 sec.)



• Validation of the Discrete Beam Model:– Material Properties (honeycomb):

To determine the material properties several quasi static tests were performed:

• Loading in T, L, W- Directions• Multidirectional shear

Testing Device - Cellbond

Principle Set up: Testing Load Curves:Lowering of force level with increasing angle

Deformed Specimen



• Validation of the Discrete Beam Model:– Material Properties (honeycomb):

15°

30°

45°

Deformed Specimen – 15°



Simulation and Validation Multi Shear – 5052 TW :

In the validation calculations the model shows:

– Good global and local deformation behaviour

– Good correlation with the tested force

Test_MSTW15°

Test_MSTW30°

1st Test_MSTW45°2nd Test_MSTW45°



• Validation of the Discrete Beam Model:– Component Testing (honeycomb, glue and cladding):

Test Setup Main Block Specimen Bumper Specimen

For the next step in validation, specimens with cladding were cut out of the bumper and the main block:

– Impact with different punch forms (spherical, cylindrical, rectangular)

Output:– Force levels for honeycomb deformation– Glue failure– Cladding deformation / rupture



• Validation of the Discrete Beam Model:– Component Testing (honeycomb, glue and cladding):

Current barrier prototype shows :– Highest accuracy

– Shortest calculation time– Greater model stability

Number of Elements: Component TestCPU – Time (min): Component Test

050

100150200250300350400450500550600

PI

PIIBen

chm

ark1

Benchm

ark2

Shells

Solid-B

eam

s

0

5000

10000

15000

20000

25000

30000

PI

PIIBen

chm

ark1

Bench

mark2

Shells

Solid-

Beams

Dis. Beams Schells Solids

Macro Elements Model

Error Termination



• Validation of the Discrete Beam Model:– Full Barrier Testing:

Three rigid test objects were defined to be hit as targets for a full barrier test:

– Rigid Rocker (with full overlap towards the barrier rocker)

– Two narrow beams (to punch the bumper locally)

– Rigid Rocker and B-Pillar (with partial overlap of the rocker � rotation)

I. Rigid Rocker II. Narrow Beams III. Rigid Rocker and B-Pillar

Real Test and Simulation with “rocker and B-pillar”




Benchmark 1Benchmark 1 Benchmark 2Benchmark 2

Beam Model - Prototype 1TestingTesting

Result of First Full Barrier Prototype:– Note: prototype not completely validated yet– Better deformation behaviour compared to Benchmark models– Initial elastic stiffness shows good correlation

Real test 1Real test 2Beam Model PT1Benchmark 1Benchmark 2

Test 1 kin.Test 2 kin.Test 1 int.Test 2 int.Beam PT1 kin.Beam PT1 int.




Undeformedstructure

Undeformedstructure

• Real Test – laser measurement• Simulation

Number of Elements: Barrier Models

0

50000

100000

150000

200000

250000

300000

PI PII Benchmark1 Benchmark20

50

100

150

200

250

300

350

400

450

500

550

600

PI PII Benchmark1 Benchmark2

CPU-Time (minutes)

The Current First Prototype Already Shows:– Localisation of the deformation bands– Rotation and rupture of the bumper– Low CPU Time

– High Stability


Conclusion:

This new modelling method presented shows:– Simulated deformation modes are as seen in the

tests– Principle tests have been validated

� barrier is based on physical properties– No non physical tuning out of experience

required– Low CPU time at a higher resolution– Constant time step– Good correlation in subsystem and full barrier

tests – Method is valid for any honeycomb material

(e.g. ODB-front)


Conclusion:

• Next Steps / Current Projects:– Build up of fully validated IIHS Barrier– ODB Front Barrier development– Further projects on spotweld(5) and material failure;

riveting, gluing, fuel system failure…

• Contact:Bernhard FellnerR&D Crash & Safety, Magna Steyr Graz

+43 676 8240 [email protected]


References:

• Journals/Magazines:(3) Tomasz Wierzbicki, “Crushing Analysis of Metal Honeycombs.”, Int. J. Impact Engineering, Vol. 1, No. 2 (1983), P. 157-174(4) Qing Zhou, Robert R. Mayer, “Characterization of Aluminium Honeycomb Material Failure in Large Deformation Compression,

Shear, and Tearing.”, Journal of Engineering Materials and Technology, Vol. 124 (October 2002), P. 412-420

• Thesis(2) Andreas Klotz, “Untersuchung von empirischen Ansätzen zur FEM-Modellierung von Crash Barrieren”, FH Joanneum, Graz,

2007

• Conference Papers:(1) Arno Eichberger, “A NOVEL VIRTUAL DEVELOPMENT PROCESS FOR SIDE IMPACT AT MAGNA STEYR BASED ON

NUMERICAL SIMULATIONS VERIFIED BY COMPONENT TESTING”, EUROSIM, 2007

(5) Thomas Heubrandtner, “Advanced Spot Welds for Crash Simulations“, European HTC, 2007

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