Challenges in the Simulation of Car Body Structures made from Composite Materials

Challenges in the Simulation of Car Body Structures made from Composite Materials Jochen Döll, Nico Feindler, Audi Lightweight Design Center

5th European HyperWorks Technology Conference,

Bonn 7.-9. Nov. 2011

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Agenda

► Trend towards Multi-Material-Design including CFRP applications

► Challenges for the simulation process

► Characteristics of composites - methods and quality of prediction

► Progresses in the simulation of FRP body structures

► Simulation of CFRP-crash-structures in full vehicle models

► Ply book definition of a front bonnet

► Summary

Jochen Döll, Nico Feindler, Challenges in the Simulation of Car Body Structures made from Composite Materials, 09.11.2011

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Trend towards Multi-Material-Design Reversal of the weight spiral


• Initiation by

lightweight

body design

• light, sportive,

less fuel consumption

• Lightweight design

measures in detail (all

departments)

• Downsizing

Power Train

• Secondary effects

e.g. Fuel tank etc.

We

igh

t R

ed

uct

ion

- kg

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Trend towards Multi-Material-Design Flexible material architectures driven by product and demands


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Challenges for car body design process New tasks to develop composite car body structures

► Predictive material models for the virtual rating and advance computing of body

functions, especially in crash situations:

► A precondition for establishment of the material in series projects

► Selection of FRP and assessment of suitability in body structures with a flexible

material policy, in particular with regard to crash disciplines

► Target: Lighter than Audi-Space-Frame - ASF

► A suitable CAE-CAD data interface

► Optimization tools with regard to the wide variety of design parameters

► Delta Alpha simulation and forecasting of critical construction methods

► Continuous simulation of processes and properties


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Modeling composites - behavior and quality of prediction Anisotropy und Stiffness (linear elastic)


► Covered by CLT, included in most FE-Solvers

► Additional effort for defining fiber orientations

► Methods for optimization fiber orientation and stack up are established and in use (Altair, Optistruct)

Time and effort Q

ua

lity

of

pre

dic

tio

n

high

hig

h

Stiffness and anisotropy

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Modeling composites - behavior and quality of prediction Ply Failure


► Essential for any crash simulation

► Needs extensive material characterization

► Know how for fitting and use of suitable material models (combined damage and ply failure models in use)

Time and effort Q

ua

lity

of

pre

dic

tio

n

high

hig

h

Ply Failure

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Modeling composites - behavior and quality of prediction Failure between plies - Delamination


► Failure mode leads to significant reduction of load carrying capacity and structural integrity

► Modeling in full vehicle models possible but moderate accuracy (coarse discretization)

► Needs FE-discretization through the thickness and characterization of additional material parameters Time and effort

Qu

ali

ty o

f p

red

icti

on

high

hig

h

Delamination

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Modeling composites - behavior and quality of prediction Example – Pole test of an Al/CFRP floor structure (Ply failure + Delamination)


Test Simulation

Conta

ctforc

e P

ole

Intrusion pole

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Time and effort Q

ua

lity

of

pre

dic

tio

n

high

hig

h

Crushing

Modeling composites - behavior and quality of prediction Crushing / Fragmentation


► Classic FE-modeling doesn’t work on macroscopic level for that failure mode

► Most state-of-the-art approaches are not satisfying (non predictive, many complex hardware tests)

► New efficient numeric method with simple material testing developed and in use at Audi

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Ply book definition using Optistruct Engineering of a lightweight front bonnet

Jochen Döll, Daniel Werum, Challenges in the Simulation of Car Body Structures made from Composite Materials, 09.11.2011

Explosion view of CFRP-concept bonnet

► Task

► Ultra lightweight design

► Meet pedestrian protection

requirements

► Design same properties compared

to aluminium version (series) for

stiffness, deformation under wind

load and HIC

► Adopt geometry of aluminium

concept (tooling was fix)

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Ply book definition using Optistruct Sensitivity analysis of fibre orientation using free size optimisation

0° 90°

45° - 45°

Specific fibre orientations are sensitive when matching the orientation of an existing load path


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Ply book definition using Optistruct Interpretation and engineering of an optimal fabric

90° +x°

Realisation via simple Triax-NCF Fibre orientation fits load paths

• Triax Fabric for optimal stiffness

• Thickness sizing according HIC-Targets


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Ply book definition using Optistruct Performance of manufactured CFRP front bonnets

P05L

Simulation:

Test 1-3:

Head Impact Deformation at Wind Load [mm]

Test / Simulation

► Good correlation between simulation and test

► CFRP-bonnet concept fulfils all requirements and functions

► 30 % lighter than full-aluminium bonnet (series)


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Summary

► Realization of advanced Multi-Material-Concepts including composite materials

needs suitable simulation tools useable within industrial development routine

► Aspects like anisotropy and ply failure important for basic design process are well

covered with current FE-Codes and simulation techniques

► Simulation and prediction of delamination and especially crushing mode in full

vehicle models is a challenge (not state of the art in many FE-Codes)

► At Audi a new method is developed and used to design and predict the behavior of

new CFRP crash structures

► To ensure maximum lightweight potential composite materials have to be designed

anisotropic as much as possible by using composite optimization tools (Altairs

Optistruct)
