Environmentally Benign Repair of Composites Using High Temperature Cyanate Ester Nanocomposites

WP-201108

Objective

The objective of this project is to demonstrate and validate a new class of environmentally benign, low viscosity cyanate ester resins and composites for the repair of advanced bismaleimide (BMI)/carbon-fiber composites for the AV-8B and the JSF weapons platforms.

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Technology Description

A new class of extremely low viscosity, nanofiller reinforced resins based on bisphenol E cyanate ester (BECy) has been developed that results in a cured polymer with excellent mechanical properties and a high degree of cross-linking. Through initial SERDP support ( WP-1580), this system has been shown to be an excellent candidate for the repair of high temperature, polymer matrix composite (PMC) based structural parts used on advanced Department of Defense air vehicle systems. The use temperature limit for the BECy system is high because of the polymer's glass transition temperature (Tg) of greater than 500°F (260°C) and onset of decomposition above 750°F (400°C). The prepolymer also has very low toxicity, contains negligible volatile organic compounds (VOCs), and has near infinite room temperature stability, facilitating reduced wastes due to spoilage compared to traditional thermosets.

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Interim Results

Through the earlier SERDP project, the cure kinetics and thermo mechanical properties of the cyanate ester systems have been thoroughly investigated. BECy generates negligible VOCs and hazardous air pollutants when compared to a benchmark epoxy resin. The adhesive strengths of these resin systems have been thoroughly investigated on BMI/carbon-fiber composite substrates using lap shear, short beam shear bending, double cantilever beam, and hole plate shear. In all cases, BMI composites repaired with BECy performed better than repairs made with an epoxy.

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Benefits

This technology will reduce (1) the environmental hazards associated with the current composite repair process, (2) the high maintenance costs associated with replacing expensive high temperature BMI-based PMC airframe parts (which are currently removed from service due to a lack of a suitable repair strategy), and (3) the amount of associated solid landfill waste of un-repairable (scrapped) BMI components. Replacing BMI airframe composite components constitutes a significant maintenance cost to the Navy. Though no one-to-one comparison data is available for repair versus replacement cost for a specific legacy airframe part type, there is a general trend of replacement costs being roughly 10 times greater than the cost of repair for a range of aircraft composite part types. The impact of this cost to the NAVAIR operations and maintenance budget is significant.

As the F-35 incorporates a significantly greater percentage of BMI composite (21%) compared to recently deployed (V-22) and legacy platforms (AV-8B, 3.5%), the development and transition of an effective BMI repair methodology would correlate into a higher return on investment (ROI) cost savings and environmental impact for this platform. The resin infusion repair process is also particularly desirable for low observable (LO) aircraft like the F-35 because the repair can be performed without significantly altering the stealth characteristics of the structure. (Anticipated Project Completion - 2014)

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Points of Contact

Principal Investigator

Ms. Kristine Obusek

Fleet Readiness Center East

Phone: 252-464-7159

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