Luna has developed conductive structural adhesives for commercial and military aerospace applications.  These adhesives combine the mechanical strength of industry standard structural adhesives with the electrical conductivity of common conductive adhesives.

The Need for Electrically Conductive Structural Adhesives

With an increased use of composites, maintaining skin conductivity between structural elements and in repair applications has become a significant challenge for engineers and designers.  Current manufacturing techniques involve the use of a non-conductive structural adhesive for component bonding, and often a second conductive adhesive or ground strap is then used to span the gap to maintain skin conductivity.  The use of multiple adhesives and additional grounding strategies results in complex, costly, and time consuming process.

Technology Summary

Luna is offering innovative, two-component, epoxy adhesives that combine the strength of a structural adhesive with the conductivity of an electrical adhesive.  Luna currently has two formulation variants which balance the need for adhesive strength and electrical conductivity.  Existing Luna formulations should meet most field applications, but the flexibility of the platform allows for custom tailoring as needed.  Luna XPN1 is a nickel-filled system and Luna XPC1 is an all carbon variant for nickel intolerant applications.

Performance

Luna’s conductive structural adhesives will save assembly time, reduce overall weight, reduce material waste, and reduce cost.  Luna conductive structural adhesives exhibit comparable physical and mechanical performance properties to Hysol EA9394, a structural adhesive that is widely used in the aerospace industry.  The lap shear tensile strength of Hysol EA9394 is measured to be 4600 psi, which is slightly less than the tensile lap shear strength measured for Luna XPN1 and XPC1.  The viscosity of Hysol EA9394 is measured to be 890 Poise, similar to the viscosity of Luna conductive adhesive systems.  Like Hysol EA9394, Luna conductive structural adhesives are easily mixed and applied by hand.  Adhesive viscosities are suitable for injection bonding, butter bonding, and some filling/potting applications.

Both XPN1 and XPC1 have demonstrated performance for use in bonding applications for ESD protection, EMI shielding, and possibly lightning strike dissipation.  Luna XPN1 exhibits a total mass loss (TML) of 0.82% and collected volatile condensable materials (CVCM) of <0.01% when tested per ASTM E595.  Luna XPC1 outgassing properties have not been measured but XPC1 is expected to be less volatile than XPN1. 

MMM-A-132B federal specification performance and adhesive performance on conductive substrates detailed on back of this technology summary.

 

LUNA XPN1

LUNA XPC1

Adhesive Description

Nickel Filled

Carbon Filled

Tensile Shear Strength

5100 psi

4950 psi

5 mil Bondline Resistance

0.08 ohm

0.5 ohm

20 mil Bondline Resistance

0.09 ohm

2 ohm

Volume Resistivity

50 ohm-cm

250 ohm-cm

Viscosity

970 Poise

615 Poise

  •  Tensile lap shear strength measured per ASTM D1002
  • Resistance measured using brass plugs per ASTM D2739
  • Viscosity measured using Brookfield spindle #5
  • Resistivity measured using four-point probe method on cured adhesive bars

Advantages of Luna’s conductive structural adhesives include:

  • 2-in-1 Adhesive:  Good electrical conductivity coupled with adhesive strength eliminates the need for both structural and conductive adhesives.
  • Reduced Weight:  Elimination of separate structural and electrical adhesives leads to lower system mass.
  • Reduced Cost:  Inexpensive raw material additives and elimination of two separate adhesives leads to reduced material costs.
  • Improved corrosion performance:  Luna is using conductive fillers that offer corrosion performance superior to traditional silver-filled adhesives.
  • Increased Assembly and Repair Speed:  Use of one adhesive instead of two will speed assembly and repair.
  • Multiple Applications and Material Versatility:  Flexible design approach allows other adhesive systems to be enhanced using similar methodology.

MMM-A-132B Federal Specification Performance

Luna XPN1 and XPC1 adhesives meet or exceed the listed hot/wet, fluid immersion, and elevated and low temperature tensile shear performance requirements per MMM-A-132B for a Type I, Class 3, Form P adhesive classification.  Adhesives applied to PAA BR-127 primed AA2024-T3 substrate at 6 to 10 mils bondline thickness.  Test specimens were bonded under 35 psi pressure and cured for five days in ambient conditions.  Tensile lap shear strengths were measured per ASTM D1002.

Performance on Conductive Substrates

Luna XPN1 and XPC1 exhibit comparable tensile shear strength when used in bonding M55J/RS3C carbon fiber composite and AC-130 treated AA2024-T3 substrates.  Single lap shear tensile tests performed per ASTM D1002.

 

                                      M55J/RS3C            AC-130 Treated Carbon Fiber Composite      AA2024-T3

Hysol EA9394

2288 psi

3284 psi

LUNA XPN1

2277 psi

2730 psi

LUNA XPC1

2267 psi

3623 psi

Technology Progress and Availability

Luna is currently demonstrating scale-up production methods and preparing for additional evaluations of adhesive performance post thermal cycling and radiation exposure.

Luna XPN1 and XPC1 adhesive kits are available for sampling to interested customers.  For sample information contact:  goffa@lunainc.com.

This material is based upon work supported by the United States Air Force under Contract No FA8650-08-C-5009.  Any opinions, findings and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the United States Air Force.