Element Sizes in Crash Calculation - DYNAmore GmbH

Element Sizes in Crash Calculation

Dipl.Dipl.--IngIng. . UdoUdo JankowskiJankowski, , Dr.Dr.--IngIng Martin MMartin Müüller ller BechtelBechtel, Dipl., Dipl.--Ing. Ing. Manfred Manfred SansSans, Tecosim GmbH, Tecosim GmbH

4. LS4. LS--DYNA Forum, 20.DYNA Forum, 20.--21. Oktober 2005,21. Oktober 2005, BambergBamberg

Agenda

Tecosim-best partner for simulation

Introduction

FE Experiments with varied parameters

Analysis of Results/ Conclusion

Outlook

Investigation on mesh density in LS Dyna

© 2005 Copyright by DYNAmore GmbH

4. LS-DYNA Anwenderforum, Bamberg 2005 Modellierung

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AMG

AutolivBayer AGBentlerBertoneBosch/ BlaupunktDegussa-Hüls AGDynamit NobelEADSFaureciaGetragHella KGJohnson ControlsKarmannLearMagnaThyssenkruppTRW AutomotiveMahleMANMannesmann/SachsSiemens VDOWagon Automotive

Audi AGAdam OPEL AGClaasDaimler ChryslerDaihatsuFiatFORDGeneral MotorsHONDAISUZUKIAJohn DeereJaguarLandroverNissanPORSCHE AGToyota

LeonbergLeonberg Basildon (UK)Basildon (UK) Coventry (UK)Coventry (UK)

Rüsselsheim

Köln

Locations & References

Igenie OfficeIgenie OfficeTokio (Japan)Tokio (Japan)

CAE PortfolioCAE Portfolio

SafetySafetyCRASHCRASH

NVH / DurabilityNVH / Durability

CFD

PowertrainPowertrain

Multi Body Systems Multi Body Systems (MBS)(MBS)

Software devSoftware devOptimizationOptimization

CPU time

0

100

200

300

400

500

600

700

800

900

1 2 3 4 5 6 7 8

CPU #

CPU

tim

e [s

] standardscale_cscale_c2scale_xscale_y

SeatsSeats

CAE Portfolio


Modellierung 4. LS-DYNA Anwenderforum, Bamberg 2005

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Any sufficiently advanced technology is indistinguishable from magic.

„Profiles of the future“ (1961) by Arthur C. Clarke (2003)

Introduction

Why do we simulate?Why do we simulate?

Introduction

Cost effectiveCost effective

FastFast

Proven methodProven method

We cannot test!We cannot test!



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Number of Elements for a FE Crashmodel BIW

0

500000

1000000

1500000

2000000

2500000

1999 2000 2001 2002 2003 2004

# of Elements

Introduction

How should a mesh look like?

Introduction

TEC|ODM Mesh Element size 12 mm TEC|ODM Mesh Element size 4 mm

TEC|ODM Mesh Element size 6 mm



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Simple box crash experiment:Box section 50 mm x 80 x 500mm, t= 1.0mm, mild steel

Varied parameters:

average edge length 15/10/5/2,5mmmesh orientation 0deg/ 25degdifferent mesh/ integration method: Belytschko-Tsay/ Fully IntegrationVaried number of spotweldsWith and without mapping or stamping dataRenumbering and move in space

Objective:

Is the result depending on the element length?

Is the result depending on the element orientation?

How does mapping influence/stabalise the results?

How do small changes in the input influence the results?


v10_1: 10mm mesh, 0degmax internal energy 6766Nmmmax displacement 278mm

analysis: defomation plots




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V10_1n: 10mm mesh, 0 deg, full integrationmax internal energy 6499Nmmmax displacement 241mm








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v10_3: 10mm triangle meshmax internal energy 6428Nmmmax displacement 215mm





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v10_4: 10mm mesh, 25deg, more spotweldmax internal energy 6560Nmmmax displacement 265mm



V10_4n: 10mm mesh, 25 deg, more spotweld, full integrationmax internal energy 6741Nmmmax displacement 295mm





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v10_5: 10mm mesh, 0 deg, more spotweldmax internal energy 6565Nmmmax displacement 262mm



v10_6: 10mm mesh, 0deg mapped stamping data MpCCI

max internal energy 6658Nmmmax displacement 235mm





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v10_6n: 10mm mesh, 0deg mapped stamping data DYNAIN






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Analysis: comparison of Displacement10mm meshing

0,00E+00

5,00E+01

1,00E+02

1,50E+02

2,00E+02

2,50E+02

3,00E+02

3,50E+02

0,00

5,00

10,0

0

15,0

0

20,0

0

25,0

0

30,0

0

35,0

0

40,0

0

45,0

0

50,0

0

55,0

0

60,0

0

65,0

0

70,0

0

75,0

0

80,0

0

85,0

0

90,0

0

95,0

0

100,

00

Time [ms]

Dis

plac

emen

t [m

m]

10_1 max 279,7910_2 max 294,5610_3 max 215,1610_4 max 265,3010_5 max 262,4710_6 max 227,1010_6n max 250,6310_7 max 302,0810_7n max 232,63




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v5_5: 5 mm mesh, 0 deg, more spotweldmax internal energy 6466Nmmmax displacement 295mm








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v5_3: 5mm triangle meshmax internal energy 6425Nmmmax displacement 265mm



V5_4: 5mm mesh, 25deg, more spotweldmax internal energy 6327Nmmmax displacement 277mm





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Analysis: comparison of Displacement5mm meshing

0,00E+00

5,00E+01

1,00E+02

1,50E+02

2,00E+02

2,50E+02

3,00E+02

3,50E+02

0,00

5,0010

,0015

,0020

,0025

,0030

,0035

,0040

,0045

,0050

,0055

,0060

,0065

,0070

,0075

,0080

,0085

,0090

,0095

,00

100,0

0

Time [ms]

Dis

plac

emen

t [m

m] 5_1 max 295,75

5_1n max 276,585_2 max 278,375_3 max 264,945_4 max 276,875_5 max 295,215_6 max 269,775_6n max 267,515_7 max 276,485_7n max 277,82


v2.5_1: 2.5mm mesh, 0degmax internal energy 6398Nmmmax displacement 296mm





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V2-5_1n: 2.5 mm mesh, 0 deg, full integrationmax internal energy 6439Nmmmax displacement 291mm



V2-5_5: 2.5 mm mesh, 0 deg, more spotweldmax internal energy 6423Nmmmax displacement 289mm





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V2-5_2n: 2.5 mm mesh, 25 degmax internal energy 6471Nmmmax displacement 287mm



v2.5_3: 2.5mm triangle meshmax internal energy 6448Nmmmax displacement 279mm





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Analysis: comparison of Displacement2.5mm meshing

0,00E+00

5,00E+01

1,00E+02

1,50E+02

2,00E+02

2,50E+02

3,00E+02

3,50E+02

0,005,00

10,0015,00

20,0025,00

30,0035,00

40,0045,00

50,0055,00

60,0065,00

70,0075,00

80,0085,00

90,0095,00

100,00

Time [ms]

Dis

plac

emen

t [m

m]

2.5_1 max 297,532.5_1n max 290,502.5_2n max 287,302.5_3 max 278,792.5_5 max 288,752.5_6 max 293,742.5_6n max 297,342.5_7 max 282,872.5_7n max 311,40


V2-5_4n: 2.5 mm mesh, 25 deg, more spotweldmax internal energy 6477Nmmmax displacement 280mm





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v2.5_6: 2.5mm mesh, 0deg mapped stamping data MpCCI




v2.5_7: 2.5mm mesh, 25deg mapped stamping data MpCCI






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v2.5_6n: 2.5mm mesh, 0deg DYNAINmax internal energy 6360Nmmmax displacement 297mm



v2.5_7n: 2.5mm mesh, 25deg DYNAINmax internal energy 6392Nmmmax displacement 311mm





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Analysis: Comparison max. displacement

Compression is nearly independent from the element length in a range from 10mm to 2.5 mm for the same element orientation

0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

0 1 2 3 4 5 6 7 8 9 10 11 12

average element length [m m]

max

dis

plac

emen

t [m

m]

c


Analysis: Comparison max. displacement

The max displacement difference for 0° mesh and 25° mesh is small for finer meshes and big for coarser meshes

0

2

4

6

8

10

12

14

16

18

20

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

averag e element leng t h [ mm]

cc




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Analysis: Influence on mesh translation and reumbering

For 10 mm the variation is about 8mm where as the deviation for smaller elements sizes is about 3mm for the same element orientation


150 00

200,00

250,00

300,00

350,00

3.5_1 max 289,053.5_1_ren max 289,053.5_1_dis max 286,293.5_1_ren max 288,70

200,00

250,00

300,00

350,00

2_1 max 290,092_1_ren max 290,092_1_dis max 293,09

150,00

200,00

250,00

300,00

10_1 max 279,7910_1_ren max 271,6410_1_dis max 278,53

Analysis: Influence on results of very small elements.

For 1,25 mm the BT (typ2) element seems to be to weak. For smaller elements sizes, full integration seems to have better results.


C o m p a r is o n o f F u l l In t e g r a t io n

0 ,0 0 E + 0 0

5 ,0 0 E + 0 1

1 ,0 0 E + 0 2

1 ,5 0 E + 0 2

2 ,0 0 E + 0 2

2 ,5 0 E + 0 2

3 ,0 0 E + 0 2

3 ,5 0 E + 0 2

0,00

6,00

12,00

18,00

24,00

30,00

36,00

42,00

48,00

54,00

60,00

66,00

72,00

78,00

84,00

90,00

96,00

T im e [m s ]

Dis

plac

emen

t [m

m]

2 .5 _ 1 n m a x 2 9 0 ,5 02 _ 1 n m a x 2 8 2 ,7 31 .2 5 _ 1 n m a x 2 9 6 ,7 8

C o m p a r is o n o f B T

0 ,0 0 E + 0 0

5 ,0 0 E + 0 1

1 ,0 0 E + 0 2

1 ,5 0 E + 0 2

2 ,0 0 E + 0 2

2 ,5 0 E + 0 2

3 ,0 0 E + 0 2

3 ,5 0 E + 0 2

0,00

5,00

10,0

0

15,0

0

20,0

0

25,0

0

30,0

0

35,0

0

40,0

0

45,0

0

50,0

0

55,0

0

60,0

0

65,0

0

70,0

0

75,0

0

80,0

0

85,0

0

90,0

0

95,0

0

100,

00

T im e [m s ]

Dis

plac

emen

t [m

m]

2 .5 _ 1 m a x 2 9 7 ,5 32 _ 1 m a x 2 9 0 ,0 91 .2 5 _ 1 m a x 3 0 3 ,9 2



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Analysis: comparison max displacement variation


variation for different mesh sizes

150

170

190

210

230

250

270

290

310

1 2 3 4 5 6 7 8 9

run

dis

pl.

(mm) 10mm

5 mm

2.5 mm

Analysis: Comparison of integration method

Calculation Time

CPU Time [s]

0,00E+00

2,00E+03

4,00E+03

6,00E+03

8,00E+03

1,00E+04

1,20E+04

1,40E+04

1,60E+04

1,80E+04

10_1

/10_1

n

10_2

/10_2

n

10_4

/10_4

n

5_1/5

_1n

5_2/5

_2n

5_4/5

_4n

2.5_1

/2.5_

1n

2.5_2

/2.5_

2n

2.5_4

/2.5_

4n

Belytschko-TsayFully Integration




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Results

Results for the displacement and the internal energy seem to be smooth and stable in a range from 15mm to 2,5 mm for orthogonal element orientation

Different element orientation give different results for coarser meshes

Finer mesh is not so sensitive for different element orientation, integration method, number of spotwelds, mapping, small changes in the input (renumbering, moving the model in space)

Mapping tools are easy to use for Crash coupling. The influence of the mapping was getting smaller for smaller element sizes for the influenced zone was getting smaller and the crash mode was very stable in our example.


Conclusion

If you know the collapse mode of a part you can use a coarse mesh which should be orthogonal in the collapse direction (so you can achieve “superconvergence”)

If you doesn't know the collapse mode of a part; Please use finer meshes

No one knows the exact collapse mode of all the parts in a vehicle!

Meshing rules for orthogonal /Mapping/Integration schemes meshes are important for coarser meshes but not important for finer meshes.

Creation of finer meshes can be automated by TEC|ODM!




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Outlook

The crashbox sample will be applied to a complete vehicle to find out about the time saving potential and the influence on the results.

Analysis of Results/ Outlook

Thank you for your attention!Please ask some questions



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Documents

Element Sizes in Crash Calculation - DYNAmore GmbH