Engineered Sealing and Structural Solutions

For the Worldwide Automotive Industry

14 November 2011 Confidential

Multidomain technics applied to

Digimat / Radioss simulations: How to use advanced material modelling features

with acceptable calculation time ?

Frank Braymand

Agenda

2

Product overview

A real application

Why are we using digimat ?

What is multi-domain ?

Integrative simulation with Digimat

Conclusions

Radioss/Digimat application

Pamcrash/Digimat application

What is digimat ?

HOW CBS® WORKS ?

3

“Buckling”

CBS® keeps the stability of

the cross section

High strength

expandable

bonding

Carrier

- Thermoplastic

- BMC

- aluminum

- steel

HOW CBS® WORKS ?

4

• HEAT ACTIVATED SEALING AND STRUCTURAL FOAMS

DESIGN IN MULTIPURPOSE APPLICATION – CITROEN C4 PICASSO

5

CBS® solution was preferred from the very beginning of the body

design for full weight and performance benefit.

New generation concept to fulfill several purposes :

- crash (front, rear, side)

- roof crush

- NVH (dynamic stiffness)

- acoustic

EuroCarBody Award 2006

Total 7,000 vehicles / week

Weight saving :

12 kg / vehicle

Agenda

6

Product overview

A real application

Why are we using digimat ?

What is multi-domain ?

Integrative simulation with Digimat

Conclusions

Radioss/Digimat application

Pamcrash/Digimat application

What is digimat ?

Some material specificities of short fiber reinforced polyamide

7

The material properties are influenced by fiber orientation

and influenced by strain

rate dependency

0 deg

45 deg

90 deg

ISO

Along the part

Gating

Fiber orientation distribution : anisotropic material properties

Flow direction

Hig

h b

end

ing

Lo

w t

ensi

le s

tiff

nes

s

Th

ickn

ess

Through the thickness

High tensile

Low bending stiffness

Anisotropic

material

properties

What is Digimat ?

9

• Material models library, based on homogenization methods (Mori-Tanaka) – For multi-phase (composite) materials

– Coupled simulations rheology/mechanics

– Commercial product, opened and documented (no black box)

• Already linked with major CAE software – Abaqus,

– LS Dyna,

– Pamcrash,

– Radioss crash (cf. L&L Products paper HTC 2009)

– Radioss Bulk (cf. L&L Products paper HTC 2010)

Robust design (material/process handling)

Optimal design (weight, cost vs performance)

Material identification process

10

The material model is defined by :

• Matrix material data – Density

– Property type (elasto-plastic, viscoplastic, …)

– Failure criterion

• Fiber material data (similar as above)

• The fiber phase is defined also by : – Fiber content

– Fiber orientation tensor (from Moldflow or others)

– Fiber length distribution

– Fiber aspect ratio (length/diameter)

Results – Tensile test ISO 527 1B

11

With a unique material dataset, Digimat can

capture the orientation effect

Why are we using Digimat ?

• To get reliable results through a better and

realistic material description

• Main drawback :

– calculation time is drastically increased

• Solutions

– Use more processors

– Improve the algorithms (E-Xstream)

12

Why are we using Digimat ?

• To get reliable results through a better and realistic material description

• Main drawback :

– calculation time is drastically increased

• Solutions

– Use more processors

– Improve the algorithms (E-Xstream)

• Direct benefits will be found when developping a

single component out of a structure

• What happend when the component is

implemented in a structure in a real project ?

13

Body in white

• 60 000 nodes,

• 56 000 elements

Barrier

• 44 000 nodes,

• 35 000 elements

Reinforcement

• 33 000 nodes

• 34 000 elements

Hardware/Software

• 16 procs Intel Xeon 3 GHz

(2007), Linux.

• Radioss 10.0.4

• Digimat 4.1.2

Side crash 150 000 elements, # 25 % digimat elements

14

Public domain snapshots.

Digimat / explicit time step best practices

15

• Decrease the time step (5 to 10 times lower) to

reduce load increments, and have convergence,

• Decreasing again the time step is also better

than having long digimat loops

• Reducing the time step of a full model for a

reduced set of elements is a waste of time and

ressource.

• A solution is to use multi-domain technics.

For each time step

Agenda

16

Product overview

A real application

Why are we using digimat ?

What is multi-domain ?

Integrative simulation with Digimat

Conclusions

Radioss/Digimat application

Pamcrash/Digimat application

What is digimat ?

What is multi-domain ?

• Main idea : split the model in two (or more) models.

• These models will run in parallel

– With differents time steps

– With their own processors

17

Model A

(na procs)

Model B

(nb procs) Master

process

• Split the models

in two slave input decks,

and create a master deck

• Define connections between each model

• Set how many processors are needed for each

model so that each single process run in parallel.

• That’s it ! Specifics keywords are needed for each

step, so you will use your prefered text editor …

How to use it ?

18

Model B

Time step ta

Na procs

Time step tb

Nb procs

Model A Model B

Model A

Model A Model B

• Isotropic simulation time step : 0.5 µs

• Digimat simulation time step : 0.05 µs (mono & multi domains)

• Multi-domain technics are really relevant to reduce

the simulation time.

• This result is not optimal ( more processors,

HW11, MPI, Digimat 421, …)

Side crash 150 000 elements, # 25 % digimat elements

19

Public domain snapshots.

/ 1,7

?

Mono / Multi domains results consistency

20

• Similar results

Mono / Multi domains results consistency

21

• Similar results

Mono / Multi domains results consistancy

22

• Similar failure location

Another example : 1500000 elements, 12000 digimat elements

23

Front crash (Pamcrash / Digimat).

• Digimat + monodomain option could be a No GO !

• Multi-domain technics are again relevant to reduce

the simulation time with digimat.

• Speed up = f(standard elements, digimat elements,

number of processors)

x 1/5

Public domain snapshots.

Conclusions

• Full crash model simulations using Digimat lead

to unacceptable simulation time (several weeks).

• Multi-domain technics are really relevant to use

Digimat’s benefits in car developpment (days):

– Lightweight,

– Cost efficiency,

– Predictive, robust design

• Thanks to Altair and E-Xstream for their HIGH

involvement in this work.

24

25

Update on wish list 2010 Digimat / Radioss Block

Altair + E-Xstream Product Managers

• Currently limited to 10 layers, constant thickness (20 variables layers still on going)

• Digimat user material available with Hypercrash

• Specifics outputs (SDV) readable in Hyperview.

• Radioss Block implicit in development

• Multi-Model-Coupling preprocessing not completly supported by Hypermesh-Hypercrash. Some operations are needed : files manipulations through text editor.

• Multi-Model-Coupling computation time improvement must be improved (target : over day, over night)

26

Update on wish list 2010 Digimat / Radioss Bulk

Altair + E-Xstream Product Managers

• Interface without user material (MAT8 anisotropic

material, extra pre-processing 1 h)

• Huge data files

THANK YOU FOR YOUR ATTENTION

ANY QUESTION ? Multidomain technics applied to

Digimat / Radioss & Digimat /Pamcrash : How to use advanced material modelling features with acceptable calculation time ?

Frank BRAYMAND

L&L Products - Advanced Engineering - Structure & Material Expert

frank.braymand@llproducts.eu

+33 (0) 388 478 578