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Metallic coating systems for graphite/epoxy laminated aircraft structures were developed to provide protection against moisture penetration, electromagnetic interference (EMI), paint strippers and lightning strikes. Foil coatings and pressed powder coatings were evaluated to assess their resistance to these hostile environments. The foil coatings provided a significant reduction in the moisture penetration and the associated strength loss of the laminate after exposure to humidity and humidity-thermal spiking. Techniques were developed for the application of foil coatings to graphite/epoxy laminates. Solid and perforated aluminum foil were applied to cured laminates in a secondary bonding operation. Sulfur dioxide/salt spray testing performed on foil-coated laminates did not indicate a severe corrosion problem.

Metallic coating systems for graphite/epoxy laminated aircraft structures were developed to provide protection against moisture penetration, electromagnetic interference (EMI), paint strippers and lightning strikes. Foil coatings and metal-filled resin coatings were evaluated to assess the protection ability in each of these areas. The foil coatings provided a significant reduction in the moisture penetration and the associated strength loss of the laminate after exposure to humidity and humidity-thermal spiking. Two techniques were developed for the application of foil coatings to graphite/epoxy laminates. Solid aluminum foil was applied to cured laminates in a secondary bonding operation. Perforated aluminum foil was bonded to the laminate in a cocuring operation. The cocuring application required that the laminate be prebled prior to application of the foil and final cocuring to obtain the optimum strength and thickness of the laminate. (Author)

The program objective was to improve the capability, reliability, and cost effectiveness of chemical milling when applied to selected aerospace structural materials. A completely automated, centrifugal regeneration system for titanium hydrofluoric acid etchant was designed, fabricated, and tested. This system automatically analyzes the etchant, adds fresh acid, determines the titanium concentration, and actives a centrifuge which removes precipitated titanium and reclaims the etchant. A new, styrene-butadiene maskant was developed that gives excellent line definition on titanium substrates and that can be manufactured for about one-half the cost of commercially available maskants. The feasibility of using a laser-drilled, high-energy water jet to scribe chem-milling maskants was established. Optimum chem-milling/forming methodizing sequences were established that minimize distortion of titanium alloy detail parts. Sampling and analytical techniques were established for the major pollutants emitted by chem-milling operations. Air pollution control agencies and equipment manufacturers were surveyed.

This report summarizes the results of the program to develop, analyze, and prove out a method for correcting the out-of-fairness of small boat hulls and hydrofoils by the use of a rework technique developed for composite structures. Tests of various composite material specimens were conducted to determine the most suitable material. An analysis of the bare hull drag of three representative craft was made to determine the horsepower and weight penalty paid by an unfair hull or struts and foils.