Optimization of a Composite B-Pillar

S. Menzel, Volkswagen Group Research

Dr.-Ing. T. Fuhrmann, Volkswagen

S. Beuermann, Altair HyperWorks

Dr.-Ing. B. Wiedemann, Altair Product Design

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Content

• Situation, Task & Objective• B-Pillar Audi A 8• Optimization Strategy• Results• Conclusion

SituationComposite materials allow • to adapt structures to specific applications and loading conditions, • to design lightweight, highly efficient structures.However, manufacturing may be costly and design processes complicated.

Task

Use a CAE based, optimization driven methodology to develop a composite car structure

Objective

• get a composite design which is competitive wrt. performance, weight & costs• identify a robust and efficient design methodology

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B-Pillar Audi A8 (D3)

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B-Pillar Aluminium

Reinforcement Steel

Reinforcement Aluminium

relevant load cases

• roof crush

• seat belt anchorage test

• IIHS side impact Source: IIHS Status Report

initial design (series-production)

Problem Characteristics

• highly nonlinear structural behaviour (large deformations, contact, failure,…)• large number of design variables (topology, number of layers, fiber orientation,…)

Optimization Tools available:• for large number of design variables: linear physics• for nonlinear physics: small number of design variables

Engineering Approach: 2-Step-Strategy1.Concept Optimization with simplified (linearized) model

⇒ efficient methods are available and well-established 2.fine tuning considering nonlinear effects with reduced set of design variables

(if necessary)

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Strategy

Com

posite Optim

ization Process

Optimization Strategy

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Concept P

hase

Topology Optimization(isotropic material behavior)

new concept (CAD model) → FEM model

Fine Tuning Phase

Tailoring?

Free Sizing!

Phase 1Laminate 1

Laminate 2

Number of Plies?

Discrete Parameter Opt.

Phase 2

Laminate Stacking?

Phase 3

Rule based

ply shuffling

0

45

-45

90

45 -45 0 0

45 -45 90 90 -45 45 0 0

-45 45

Patch InterpretationDiscrete Ply Thickness

Optimized Stacking Sequence

nonlinear physics

(if necessary)

Topology Optimization

• topology optimization with linear isotropic material behaviour⇒ interpretation of reinforcement ribs

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design space (ρ > 30%) obtained by optimization

View of PSOLID-Elements with density ρ > 30%

ConceptP

haseFine Tuning Phase

FreeSize-Optimization

• B-pillar with ribs-structures⇒ patch interpretation

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Ply thickness [mm]

ConceptP

haseFine Tuning Phase

Parameter Optimization

• Patch interpretation (considering manufacturing constraints) • Patch definition with PCOMPG-cards• Number of plies (still considering linear physics)

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Ply thicknes [mm]

Optimization

Concept P

haseFine Tuning Phase

Parameter Optimization

• Variant with reduced number of patches (Layup for prototype)

• Status• static stiffness of composite and metal sheet B-pillar at same level

• weight reduction approx. 40%

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5 patchesplus ribs

2 patchesplus ribs

Concept P

haseFine Tuning Phase

Testing

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exterior view

Composite-B-Pillar

interior view

• Composite Prototype• Original Design

Quasi-Static Component Crush Test

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test bench (serial B-pillar) test bench

Testing conditions:

- v = 1 mm/s

- smax = 500 mm

z-directionfree

rigidconnection

Impactor

B-Pillar

Quasi-Static Component Crush Test

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Deformation

Def

orm

atio

n En

ergy

ΔmB-Säule≈ −30%

ΔEmax ≈ +25%

Δuintr ≈ +30%

B-pillar series

B-pillar composite

Quasi-Static Component Crush Test

• Simulation: – Strain rate dependent material properties not available. Validation of simulation model not

carried out

• Test Result: Composite B-pillar with smaller force level and larger intrusion

⇒ reinforcement necessary to improve intrusion

⇒ significant weight advantages of composite

structure will disappear

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Loadcase: IIHS

Summary

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• Significant weight reduction (up to 40%) for Composite B-Pillar at same level of

static stiffness

• Effective weight reduction is limited by large intrusion (component crush test)

• Optimization methodology very efficient for linear physics

• Highly nonlinear effects need to be considered in sizing phase

Some project contents have been created within the BMBF-project BIOTEX. Therefore we would like to usethe opportunity to thank the BMBF for the financial support to realize the project.