Materials & Advanced Manufacturing (M&AM) STRUCTURAL - - PowerPoint PPT Presentation

Materials & Advanced Manufacturing (M&AM)

8/9/2018

STRUCTURAL ADHESIVE WITH COMBINED HIGH STRENGTH AND DUCTILITY FOR MULTIMATERIAL JOINING AND GALVANIC ISOLATION

Marvin Pollum, Joseph Kriley, Masa Nakajima, Kar Tean Tan, Jeffrey Stalker, Richard Fleischauer, and Brian Rearick

Funded by TARDEC in collaboration with Drexel University (W911NF-13-2-0046)

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Significant lightweighting efforts in new vehicle designs
• Implementation of dissimilar and non-metal materials

requires:

– High performance adhesives – Galvanic isolation

Introduction

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Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Researchers at ARL put forward new adhesive performance requirements

based on screening hundreds of commercial adhesives

Introduction

½” 4” Load Load Bondline 1”

Thick 2024 Aluminum Substrate ARL-SR-0371

Group I properties correlate with greatest energy dissipation

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Recently developed structural adhesive with Group I performance

Adhesive Development

Combined higher strength (>6000 psi) and displacement (>35%)

½” 4” Load Load Bondline 1”

Thick 2024 Aluminum Substrate

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Recently developed structural adhesive with Group I performance

Adhesive Development

1-component, shelf-stable, thermoset formulation

− 1-component epoxy thermoset − 160°C cure temperature − Shelf-stable >9 months

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• High strength of adhesive causing thick Al substrate to deform

Adhesive Development

Need to understand bulk material properties of adhesive

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Bulk shear properties measured independent of substrate
• Thick Adherend Shear Test (ISO 11003-2)

Bulk Material Properties

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Increased shear stress with a significant increase in shear strain
• Area under stress-strain curve = total strain energy density

Bulk Material Properties

2.5-fold increase in energy absorbed before failure

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Group I performance verified by ARL

Performance Validation

• R. Jensen et. al. 41st Annual

Meeting of The Adhesion Society. San Diego, CA. March 1, 2018.

Does prototype adhesive hold up in extreme environments?

Materials & Advanced Manufacturing (M&AM)

8/9/2018

Table 1. Retention of adhesive lap joint strength at elevated test temperature and following a variety of environmental

• conditionings. All tested on grit blasted AA2024 substrate.

Environmental Conditioning Test Temp. Lap Shear Strength (MPa) Strength Retention (%) None 25°C 43.0 ± 2.5

• None

71°C 35.4 ± 0.6 82.4 63°C water soak 14 days 25°C 33.5 ± 2.4 77.9 Salt spray (bare) 1000 hours 25°C 29.1 ± 3.2 67.6 Salt spray (primed) 1000 hours 25°C 35.4 ± 2.3 82.3

Environmental Resistance

• Tier II testing proposed by ARL,

maintain 75% initial lap shear strength:

 At elevated temperatures (71oC)  After 2 week hot water immersion

• Also maintains high strength after

corrosive conditioning (salt spray) for 42 days, especially coated with primer

Maintains strength in hot, wet, and corrosive environments

Materials & Advanced Manufacturing (M&AM)

8/9/2018

Environmental Resistance

5 10 15 20 25 Prototype Structural Adhesive

Wedge Impact Energy (N/mm)

25°C

• 40°C
• Thermoset epoxies typically lose performance at low temperatures
• High strain rate wedge impact testing (ISO 11343)

Maintains 67% of impact energy at -40oC

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Prototype Adhesive exhibits high strength and ductility while also

maintaining performance under:

 High Humidity (100%)  Elevated Temperatures (71°C)  Low Temperatures (-40°C)  Corrosive conditions (salt spray)

• Environmental resistance also confirmed by ARL

Environmental Resistance

All tests performed on Al, what about other substrates?

Materials & Advanced Manufacturing (M&AM)

8/9/2018

Table 2. Performance of prototype adhesive on hot-dip galvanized steel (HDG), carbon fiber reinforced plastic (CFRP), and in mixed material joints. Substrate Lap Shear Strength (MPa) Displace- ment (mm) Failure Mode Oiled HDG 15.6 ± 0.4 15.8 ± 2.9 Adhesive Cleaned HDG 16.3 ± 0.2 40.8 ± 0.8 Substrate* CFRP 23.6 ± 1.9 5.2 ± 0.2 Substrate* Mixed AA2024/CFRP 19.8 ± 1.5 3.1 ± 0.3 Substrate* *Substrate failure invalidates the lap shear strength and displacement values, therefore these results are qualitative

Other Substrates

• Good adhesion even to galvanized steel (even oily) and to carbon fiber
• However, substrate failure invalidates the lap joint measurements so these

results are only qualitative

Preliminary qualitative results are promising

Materials & Advanced Manufacturing (M&AM)

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• Galvanic assemblies based on methods from NAVAIR and AMCOM
• Combines carbon fiber, steel, and aluminum with fasteners and optionally

adhesives

• Significantly reduced substrate corrosion by bonding/sealing with adhesive

Galvanic Isolation

Carbon Fiber CRS AA2024

Prototype formulation does not change adhesive’s ability to galvanically isolate

with adhesive without adhesive

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• Developed an adhesive meeting Group I

specifications put forward by ARL

• Extreme displacement of prototype

adhesive due to high % strain of the bulk adhesive material

• High strain energy density of adhesive

also provides impact resistance

• Formulations changes maintain

adhesive’s resistance to extreme environments and ability to galvanically isolate mixed materials

Conclusions

Materials & Advanced Manufacturing (M&AM)

8/9/2018

• PPG Adhesives & Sealants Team
• Rob Jensen and Dave Flanagan from ARL
• Funding from TARDEC in collaboration with

Drexel University (W911NF-13-2-0046)

Acknowledgements