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Application of Adhesives and Bonded Joint Design in Improving Vehicle Structure

Performance

Mansour MirdamadiMustafa Ahmed

Matt TurpinAlan Robinson

Dow Automotive

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Presentation OutlinePresentation OutlinePresentation Outline

• Structural adhesives benefits and overview

• Selection of adhesive system

• CAE modeling for crashworthiness applications

• Frontal impact application development study

• Conclusions

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Structural Adhesives BenefitsStructural Adhesives BenefitsStructural Adhesives Benefits

Increases the stiffness of car body

Improved Durability

Safety

Improved Handling / Acoustics

Increased energy managment capability

Enables use of Advanced High Strength Steel (AHSS)

Cost Reduction

Mass ReductionEnables downgauged steel

Enables multi-material construction ( Al, Mg, & Composites

Weld spot reduction

Downgauge steel

Optimize usage for combination of AHSS grades

Highly economical joining process

Overcome fatigue problems, improve long term durability

Vehicle Assembly Overcome weld access problems

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Choice of Structural Adhesive Choice of Structural Adhesive Choice of Structural Adhesive

• Epoxy based systemsGeneral purpose

Standard grades

Semi-fracture toughened

Superior fracture toughened

• Automotive industry criterion for structural adhesivesModulus: Above 1000 MPa

Glass Transition Temperature: Above 80 °C

Impact Resistance f(T): From -40 °C to 80 °C

Oil Compatibility: Adhesion to oily substrates

Lower cure window: temperature and time

Robust to accommodate different steel coatings

Robust wash-off resistance

One component toughened epoxy is the industry choice

Hem Flange

Component Joint

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Impact Peel Test ResultsImpact Peel Test ResultsImpact Peel Test ResultsS

tren

gth

(N

/m

m)

21

12

6

0

35

12

0

44

2219

7.5

00

5

10

15

20

25

30

35

40

45

50

-40C-20C

RT

0 0

Increased ductility at low temperatures

Superior FractureToughened

Semi FractureToughened

StructuralAdhesive

General PurposeAdhesive

• Increased crash resistance• Increased durability• Increased flexibility to

down gauge metal & reduce welds

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Why Structural Adhesives?Why Structural Adhesives?Why Structural Adhesives?

• Eliminates sudden change of stresses

• Significantly lowers stress acting across joined region

• Uniformly distributes the load

• Increases load carrying capacity

• Eliminates stress concentration

Spot weld 5 mmAdhesive bond

B. Chang et al. / Journal of Materials Processing Technology 108 (2001) 307±313

High stress-concentration

High stress-concentration

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Crash Durable Adhesives (CDA) “Toughening” Principle

Crash Durable Adhesives (CDA) Crash Durable Adhesives (CDA) ““TougheningToughening”” PrinciplePrinciple

• The micromechanical behavior of the adhesive allows the reduction of stress peaks through distribution of three-axial load cases in the volume around the crack tip

• The effects of cavitations (primary toughening mechanism) are often visible

• There is a gradation of properties - dependent on pressure and state of deformation. This makes the problem extremely complex, non-linear and difficult to model the physics

ductile-unstable

d

ductile-stableF

F

F

d

brittle-unstable

d

brittle-stableF

d

d

F

F

BETAMATE CDA

Patented toughening system is the enabler for the unique impact performance

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CDA CAE Modeling ConsiderationsCDA CAE Modeling ConsiderationsCDA CAE Modeling Considerations

• Shell elements of the substrates are modeled as ‘mid-plane’

• Adhesive element is modeled with the real bond-line thickness (BLT)

• Interface contact definition is used to connect the adhesive to the substrate

Shell element (standard)

Shell element (standard)

Adhesive SOLID element

Interface Nodes to Surface -Offset

Interface Nodes to Surface -Offset

BLT

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CDA CAE Correlation to High Velocity Dynamic Test

CDA CAE Correlation to High CDA CAE Correlation to High Velocity Dynamic TestVelocity Dynamic Test

Profile thickness: 1.5 mmBondline thickness: 0.35 mm Impactor mass: 32.66 kg (72 lbs)Impactor speed: 5.17 m/s (11.57 mph)

Profile thickness: 1.0 mmBondline thickness: 0.35 mm Impactor mass: 32.66 kg (72 lbs)Impactor speed: 8.81m/s (19.71 mph)

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Application Development For Bonded Front Rails

Application Development For Application Development For Bonded Front RailsBonded Front Rails

• Front rail bonded concept developmentMany studies has been performed to show at a component level it is possible to reduce no. of spot welds and use structural bond andachieve mass reduction as a result of reduced gauges

Application of structural bonding for front rails at various OEM has not provided substantial crash and energy management performance benefits

Baseline

120 mm

70 mm

20 mm

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Front Rail Joint Design DevelopmentFront Rail Joint Design DevelopmentFront Rail Joint Design Development

Baseline

120 mm

70 mm 70 mm 70 mm

20 mm

167 mm

Design 1 Design 2

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Component Level Analysis Performance Comparison

Component Level Analysis Performance Component Level Analysis Performance ComparisonComparison

Increased energy absorption

Complete unzipping of the joint

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Full Vehicle NCAP and Offset Performance CAE Study

Full Vehicle NCAP and Offset Full Vehicle NCAP and Offset Performance CAE StudyPerformance CAE Study

Baseline Modified Bonded Joint Design

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NCAP Rail Energy ComparisonNCAP Rail Energy ComparisonNCAP Rail Energy Comparison

Energy absorption increase with new bonded joint design

Baseline design with adhesives degrades energy absorption performance

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NCAP PerformanceNCAP PerformanceNCAP Performance

New bonded joint design reduces peak acceleration

Increased opportunity for further mass reduction

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40 mph Offset Performance40 mph Offset Performance40 mph Offset Performance

• Increased energy absorption of rails allows:

Reduction of intrusion into the occupant compartment

Ability to reduce the gauge of the sheet metal

Ability to reduce no. of reinforcements

Reduction of spot welds (30-50%)

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Study FindingsStudy FindingsStudy Findings

• Successful application of adhesives in front longitudinal members requiresProper selection of steel thickness and steel grade

Proper joint design and adhesive that promotes increased energy absorption of the steel structure. The two can not be de-coupled

• Joint design in combination with proper choice of adhesive can sufficiently increase energy absorption of the rails, while providing key benefits:

Improved frontal NCAP crash pulse – reduced peak acceleration

Significant intrusion improvement into the occupant compartment

Design and packaging freedom to accommodate multiple vehicle design theme

Increased bending stiffness of rails

Reduction of spot welds (30% to 50%)

Mass reduction of 0.5 kg

Cost reduction of up to 10%. However, there could be additional cost savings due to elimination or reduction of steel gauges in other parts of the structure, i.e., rocker, front body hinge pillar reinforcement, etc.

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Great Designs in Steel is Sponsored by:AK Steel Corporation, ArcelorMittal, Nucor Corporation,

Severstal North America Inc. and United States Steel Corporation