Development of Field Level Repairs for Composite Structures,
LOCKHEED-CALIFORNIA CO BURBANK
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The composite repair programs performed by Lockheed-California Company have developed and validated field repairs for primary and secondary structures. These include both bolted repairs and bonded repairs, and the repairs are suitable for use at typical field level maintenance bases. The repairs developed for primary structures in the NADC program achieved the goal of restoring design strength levels of 4000 microinchesin strain to failure. Procedures were developed for fastener hole drilling and fastener installation under field conditions, which include use of hand tools by unskilled personnel and lack of access for use of backup blocks. Blind fasteners were evaluated, and a recently developed Bigfoot fastener was found to be satisfactory. A screening program was conducted on suitable field level adhesives which are storable ambient conditions and meet the structural and environmental requirements for repairs of primary structures. A two-part adhesive developed by NADC was found to meet these criteria. In addition, 177 C 350 F curing film adhesives which meet the structural and environmental criteria was found to have several months storability at room temperature. Environmentally durable surface treatments for titanium adherends were evaluated and found acceptable, which will permit their use in repair kits supplies to the field.