SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-121 (AirForce)
Title:  Nanocomposites for Electrically Conductive Structural Adhesives and Bolt Hole Fillers
Research & Technical Areas:  Air Platform, Materials/Processes

 The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.
  STATEMENT OF INTENT: Improve electrical properties of composite structures
  Objective:  Develop nanocomposite electrically conductive structural adhesive/bolt hole filler to demonstrate improved electrical properties of composite structures at reduced weight and manufacturing cost.
  Description:  Some nanoconstituents are becoming relatively mature, low-cost materials which have been shown to improve electrical and thermal conductivity of structural adhesives without compromising the mechanical strength. Typical adhesives use large quantities of silver particles to boost electrical conductivity, making them unsuitable for structural use. However, the addition of some carbon nanoconstituents, such as vapor grown carbon nanofibers (VGCNF) or exfoliated graphene sheets, at only a few volume percent, have shown reductions in resistance of adhesives to 15 ohms for a typical 10 mil bond thickness with no drop in lap shear strength. In addition, thermal conductivity is doubled to 2 W/mK or greater across the bond line, which may be increased with further optimization. Other nanoconstituents may show even better results in the future. These advantages could be transferred to filler materials used around bolts, etc. to impart a structure with a complete electrical path, thus reducing damage done to composite structure in the event of a lightening strike. The adhesives/fillers developed in Phase II will demonstrate the required electrical conductivity for lightening strike protection of organic matrix composite structures, while maintaining mechanical performance design properties at joints and bolt holes. The materials and articles will be tested for electrical characteristics, mechanical properties, and thermal conductivity. If feasible, some articles will be tested in a lightening strike facility. It is desired that additional quantities of these materials be delivered to the government for additional evaluation. A cost estimate for producing these materials in commercial quantities and draft material and process specifications would be required at the end of Phase II.

  PHASE I: Demonstrate the feasibility of producing at least one conductive structural adhesive and one bolt hole filler by fabricating subscale coupons and articles with the adhesives/fillers.
  
  PHASE II: Finalize the formulation of at least one aerospace-quality adhesive and one aerospace-quality bolt hole filler material. These materials will be used to build full-scale demonstration articles for lightening strike test and analysis.

  DUAL USE COMMERCIALIZATION: Military application: Satellite structures and military aircraft structures. Commercial application: Satellite structures and civilian aircraft structures.

  References:  1. Vapor Grown Carbon Nanofiber Materials and Applications Workshop held 14-15 September 2004, Kettering, Ohio

Keywords:  adhesives, conductive polymers, nanotechnology, fiber reinforced composites, electrical properties

Questions and Answers:
Q: Lap share values are different between different epoxies, for example,the lap share of toughened epoxy could be higher than untoughened epoxy, even after filling with electric conductive fillers. In another words, the lap share of toughened epoxy may drop after filling with electric conductive material, but may still higher than regular untoughened epoxy. If that is the case, could it be acceptable? It could be more clear if we can have a defined lap share value to follow.
A: . . . response pending . . .
Q: Lap share values are different between different epoxies, for example,the lap share of toughened epoxy could be higher than untoughened epoxy, even after filling with electric conductive fillers. In another words, the lap share of toughened epoxy may drop after filling with electric conductive material, but may still higher than regular untoughened epoxy. If that is the case, could it be acceptable? It could be more clear if we can have a defined lap share value to follow.
A: . . . response pending . . .
Q: Could you give examples of adhesives and bolt hole fillers to use for comparison?
A: . . . response pending . . .
Q: If testing for EMI and electrical resistivity, is it preferred that thest coupons include the underlying composite structure, or can testing be performed on just the adhesive and bolt hole filler?
A: It would be preferable to test filler alone. That way we can get the material properties with out any interference from the structure or panel.
Q: 1. Is there any expected lap share value for the conductive adhesives?
2. What is the prefered base for test coupons?
A: 1. Lap shear values should be comparable to the standard epoxy that the filler is added to.
Q: Could you give examples of adhesives and bolt hole fillers to use for comparison?
A: . . . response pending . . .
Q: If testing for EMI and electrical resistivity, is it preferred that thest coupons include the underlying composite structure, or can testing be performed on just the adhesive and bolt hole filler?
A: It would be preferable to test filler alone. That way we can get the material properties with out any interference from the structure or panel.
Q: 1. Is there any expected lap share value for the conductive adhesives?
2. What is the prefered base for test coupons?
A: 1. Lap shear values should be comparable to the standard epoxy that the filler is added to.

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