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
+33 (0) 388 478 578