Metal-hybrid structures for an improved crashbehaviour of car body structures

Michael Kriescher, Walid Salameh, Deutsches Zentrum fr Luft- und Raumfahrt e.V. (DLR), DEDr. Alexander Droste, Jan Rttger, DOW Automotive Systems

18. Mai 2010 Materialien des Karosseriebaus

Materialien des Karosseriebaus 18.05.2010, Folie 2

Motivation

collapse of the rockers and side pieces cross-section during pole-crash -> energy must be absorbed by various other componentsa stabilisation of the cross-section during bending should lead to a much higher weight specific energy-absorption of the rocker -> higher freedom of design and choice of materials for the surrounding structures, like the floor panels -> possibility of an overall weight reductionthe storage of critical components like Li-Ion batteries in the underbody requires a low intrusiondemand for a simple, lightweight concept made of relatively cheap materials, adaptable to different kinds of vehicle concepts

floor structure developed by DLR during SLC-project

Materialien des Karosseriebaus 18.05.2010, Folie 3

Basic principle

Absorption of crash energy through elongation of material

Stabilisation of cross section

stabilisation of the beam by a core structurethe core must stay intact, throughout the entire bending process, in order to increase weight specific energy absorptionsimplified LS-Dyna-calculations showed an increase in weight specific energy absorption by a factor of about 2,5

Variant Drawing Total mass [kg]

Material Energy absorption [kJ]

kJ/kg

Core: foam 400 kg/mshell: 1 mm TRIPLEX

22,39Various types of steel

4,5 0,2

Al honeycomb

15,15

Core: 1 mm Al; shell: 1 mm TRIPLEX

5,8 0,38

Reference

0,5

Foam

28,1 14

Materialien des Karosseriebaus 18.05.2010, Folie 4

Testing performed in cooperation with DOWForce-displacement curve

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0 50 100 150 200 250 300 350 400 450 500Displacement [mm]

Forc

e [k

N]

Steel section (hollow)

Steel section (foam-filled)

hollow beam, 12,35 kg foam filled beam 21,15 kg

DC 04 - beam filled with foam bythe DOW chemical companydensity 400 kg/m -> weight increase by a factor of 1,72 compared to hollow beam weight specific energy absorption [J/kg]

0,00

100,00

200,00

300,00

400,00

500,00

600,00

steel section (hollow) steel section (foam- filled)

Materialien des Karosseriebaus 18.05.2010, Folie 5

Summary structural foamsStructural and crash performance enhancementsProven technologyPotential to downgauge and/or eliminate BIW and tooling contentHave one single/downgraded platform and use bulk foams to scale performance needs for different derivates ScalabilityDesign flexibility

Foam will fill any cavity shape and contourFoam does not require re-design after sheet metal changesAutomated filling

Validated FEA-Tools available for main grades

Materialien des Karosseriebaus 18.05.2010, Folie 6

Cavity filling with BETAFOAM

BETAFOAM is a family of foam-based products

Two-component polyurethane foam applied as bulk

Fat cycle time, room temperature curing

Components form a rigid, closed cell foamFoam products range in density from 32 g/l to 641 g/l

Higher density foams provide multi-functional benefits

Materialien des Karosseriebaus 18.05.2010, Folie 7

Basic working principal structural foams

Dynamic test at 3,57m/s; 80 kgFoam adhesion to surrounding structurePrevention of bending and buckling effectsFoam is acting as a shell connecting elementIncreased energy absorption capability of complete structure

Materialien des Karosseriebaus 18.05.2010, Folie 8

v0 CAEv0 Test

v1 CAEv1 Test

v2 CAEv2 Test

v3 CAEv3 Test

Boundary Prescribed Motion Moving Rigid Wall

v1 < v2 < v3

Static Correlation Dynamic Correlation

Material model Development and validation

Static CAE

Static TEST 1

Static TEST 3

Static TEST 0

Static TEST 2

Static TEST 0Static CAE

Static TEST 1

(mm)

Foam-Filled Tube

Empty Tube

Static CAE

Static TEST 1

Static TEST 3

Static TEST 0

Static TEST 2

Static TEST 0Static CAE

Static TEST 1

(mm)

Foam-Filled Tube

Empty Tube

Materialien des Karosseriebaus 18.05.2010, Folie 9

Geometric variations

Force-displacement curve

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0 50 100 150 200 250 300 350 400 450 500

Displacement [mm]

Forc

e [k

N]

Steel section (hollow)

Steel section (foam-filled)

Steel section (sideways, foam-filled)

deformation mode stays the same for different cross sectionstest with a crosssection rotated by 90 leads to higher peak force but earlier failure of the material -> steel with a higher max. strain would lead to even better results

Materialien des Karosseriebaus 18.05.2010, Folie 10

Variation of foam density

foam density 200 kg/m -> weight increaseby a factor of 1,37 compared to a hollowbeaminsufficient stabilisation of the steel shelldue to use of low density foam -> no significant gain in weight specific energyabsorption

weight specific energy absorption [J/kg]

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100

200

300

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500

600

DC04 hollowsection

DC04 + foam 400 DC04 + foam 200

Force-displacement curve

05

101520253035

0 100 200 300 400 500Displacement [mm]

Forc

e [k

N]

steel section DC 04 with foam 400 kg/m

steel DC04 with foam 200 kg/m

steel section DC 04 hollow

Materialien des Karosseriebaus 18.05.2010, Folie 11

core remains intact, and partiallystabilises the beam

large foldbeneath thecore

H3 H2 H1

Variation of core material

use of wooden cores: high ratio of compression strength / densityhigher density than foam

further development: combination of solid corestructures and light foam

Force-displacement curve

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5

10

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20

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0 50 100 150 200 250 300 350 400 450 500Displacement [mm]

Forc

e [k

N]

DC04_H1DC04_H2DC04_H3

Materialien des Karosseriebaus 18.05.2010, Folie 12

Variation of core material (2)

wooden core H1: weight increase by a factor of 1,41 compared to a hollowbeam

weight specific energy absorption [J/kg]

0

100

200

300

400

500

600

DC04 hollowsection

DC04 + foam400

DC04 + foam200

DC04 +wooden core

Force-displacement curve

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400 450 500Displacement [mm]

Forc

e [k

N]

steel section DC 04 with foam 400 kg/m

steel DC04 with wooden core (H1)

steel section DC 04 hollow

Materialien des Karosseriebaus 18.05.2010, Folie 13

Variation of shell material

use of stainless steel 1.4301 (highertensile strength) -> weight increaseby a factor of 1,74 compared to hollow beam

weight specific energy absorption [J/kg]

0

100

200

300

400

500

600

700

800

900

DC04 hollowsection

DC04 + foam400

DC04 + foam200

DC04 + woodencore

1.4301+ foam400

Force-displacement curve

05

1015202530354045

0 50 100 150 200 250 300 350 400 450 500Displacement [mm]

Forc

e [k

N]

steel section DC 04 with foam 400 kg/m

steel section DC 04 hollow

steel section 1.4301 with foam 400 kg/m

Materialien des Karosseriebaus 18.05.2010, Folie 14

Integration into the underbody structure, basic principle

conventional rectangular topology:

difficulty in designing an appropriatesupport structure

a ring-like shaped, filled structure should lead to comparatively low strain values, distributed over a large portion of the structure

Materialien des Karosseriebaus 18.05.2010, Folie 15

LS-Dyna-Simulation results with a simplified body structure

modified pole crash:

the modified pole crash was performed to avoid the addition of virtual weights

car body is fixedweight of pole= 1380 kgspeed of pole = 29 km/hintrusion is slightly more severe compared to a regular pole crash

Materialien des Karosseriebaus 18.05.2010, Folie 16

Modified pole crash results with a simplified body structure

results of the new structure:high energy absorption, compared to a full vehicle with interior, even without floor panel, seat structure etc.proof of the basic principle: the underbody structure is deformed as one ring, without any collapse of particular parts

Materialien des Karosseriebaus 18.05.2010, Folie 17

Summary and conclusions

filling of beam structures drastically increase their intrusion resistenceand weight -specific energy-absorptionan underbody structure composed of a ring-like filled structure results in a very high intrusion resistance during pole crash. A large portion of the underbody could therefore be used for the storage of critical components like Li-Ion batteriesa more detailed car body structure is needed to make accurate weight predictionsoptimization of the structure by decreasing intrusion resistance in favor of reduced weight seems reasonable since the frame structure alone absorbs all of the crash energy, other components, like the floor panel, can be designed differently, leading to a potential weight reduction

Thank you for your attention