Application of Adhesives and Bonded Joint Design in .../media/Files/Autosteel/Great... · ¾Proper...
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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