SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-327 (AirForce)
Title:  Universal Method of Bonding Steel Repairs to Aluminum Structures
Research & Technical Areas:  Materials/Processes

  Objective:  Develop and validate a method to bond high modulus repairs onto aluminum structure.
  Description:  Bonding of isotropic, high modulus repair materials to aluminum structures are virtually non-existent in today’s Maintenance-Repair-Overhaul (MRO) environment. The limitations of composites (Low Bearing Strength, reduced Multi-axial load capability) and aluminum or titanium (Low modulus) have either left some requirements unanswered or have increased complexity and cost. Repairs with high multi-axis loading and/or tight geometry (limiting repair thickness) are needed for some applications such as the C-130. Geometry limits the thickness of the repair member and the length available to transfer the load into the repair member. The required thickness of the repair is determined by the ratio of modulus, and to a lesser extent strength of, the repair material to the original material. Geometry also requires a sheet metal tolerance level on the thickness of the repair. Currently we have a verified repair process using Ti-6, AL-4V and Boron uni-tape composite. Potential cost avoidance would be substantial since typical structures that are candidates for this type of repair (wing planks) have high replacement costs (if spares are even available). An isotropic, high modulus bondable repair material would be the best solution to this type of damage. To be effective the following characteristics must be met for the repair. a. Repair member Young’s modulus greater than 25 msi. (10msi *2.5) b. Repair member tensile yield strength greater than 90 ksi. (35ksi*2.5) c. Repair member tensile ultimate strength greater than 135 ksi. (90ksi*1.5) d. Repair material must be nearly isotropic e. Repair material must be able to be fabricated with a thickness tolerance equal to sheet metal tolerances f. Repair material must be able to be fabricated into complex shapes with edges tapered down 0.020” thick. g. After installation repair material must be capable of being drilled and reamed for installation of close tolerance fasteners through the repair. h. Repair material must be capable of being durably bonded to aluminum using adhesives that meet the requirements of MMM-A-132 Type I, class 2 and Mil-A-25463, Type I Class 2. Specialized surface preparations are acceptable but must have a minimal logistic foot print and must be robust for mil applications. Technical Order and SERDP report are available upon request.

  PHASE I: Determine if a combination of repair material, surface preparation, adhesive system, and bonding process are achievable for ensuring durable repairs to aluminum when constraints require a small repair foot print.
  PHASE II: Demonstration and validation of the repair process on aircraft or similar component. See T.O. 1-1A-1 chapter 8.

  PHASE III DUAL USE APPLICATIONS: Military application: A bonding repair process for meeting these criteria would be portable to most structural aluminum applications: weather, aeronautical, naval, automotive, or civil. Commercial application: A bonding repair process would be portable to most aeronautical, naval, and structural applications.

  References:  1. FAA Document “PS-ACE100-2005-10038”. Searchable through www.google.com/unclesam 2. FAA Document “AC 20-107”. Searchable through www.google.com/unclesam

Keywords:  bonded, repair, steel, composites, structures

Questions and Answers:
Q: 1. What kind of Al (type of Al alloy) structure?
2. Why you need steel(Which type of steel) to bond Al structure?
3. What are the repair thickness required?
A: 1. Currently because of geometry we are bolting/bonding 0.063" half hard steel onto C-130 wing skins with cracks. There is an engine attach angle common to the repair area that has a 0.063" nacelle attach angle under it. We replace the nacelle with a reversed version and run the steel doubler thru the space the original nacelle attach angle occupied.

3. The repair thickness is 0.063”. The structure being repaired is 0.115 to 0.142 7075 aluminum

2. The wing plank is made for 7075-T7651 and 7075-T651.
Q: 1. What kind of Al (type of Al alloy) structure?
2. Why you need steel(Which type of steel) to bond Al structure?
3. What are the repair thickness required?
A: 1. Currently because of geometry we are bolting/bonding 0.063" half hard steel onto C-130 wing skins with cracks. There is an engine attach angle common to the repair area that has a 0.063" nacelle attach angle under it. We replace the nacelle with a reversed version and run the steel doubler thru the space the original nacelle attach angle occupied.

3. The repair thickness is 0.063”. The structure being repaired is 0.115 to 0.142 7075 aluminum

2. The wing plank is made for 7075-T7651 and 7075-T651.

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