Built-In Damage State Detection and Localization Capabilities for Composite Engine Structures

ABSTRACT: Organic matrix composite (OMC) structures used in critical areas such as around engine inlets and exhaust wash structures are known to fail through both hygrothermal and oxidative degradation. Without a reliable means of monitoring the health of these high-temperature composites, degradation can seriously impact an aircraft"s state of readiness. At the same time, time-based maintenance in which parts are replaced on a schedule whether they need it or not is prohibitively expensive, with some structures seeing an expected service life of 100 hours or less. TRI/Austin proposes to develop a structural health monitoring (SHM) solution capable of monitoring the health of these high temperature composites in-situ. In Phase I a prototype SHM system was built and tested at elevated temperatures. Also, sample OMCs were collected and fatigue tested to failure to study their damage signatures throughout life. In Phase II, thermal and physical ruggedness of the SHM system will be further improved and its weight reduced; more complex and diverse OMC parts will be tested; algorithms correlating SHM data to time in part life will be developed, automated and installed on the SHM system; and the complete system will be demonstrated. BENEFIT: The proposed system permits a shift from conventional time-based maintenance to the more cost-effective condition-based maintenance in which a part is retired only as required. This in turn may extend the service life of composite parts used around engine inlets, exhaust wash structures, and other critical areas. Since the failure progression of OMCs are not as well understood as conventional metals, ability to monitor health and assess fitness for service is also an enabling technology for transitioning OMC structures into the fleet. Applications of this SHM system include composites with resins such as polyimides (AFR-PE-4, MVK-14 FreeForm, 900HT, PMR-II-50, DMBZY-15, PETI series, etc), bismaleimides (BMIs), cyanate esters, phenolics, benzoxazines and phthalonitriles that are reinforced with continuous fibers such as glass, quartz, or carbon/graphite. Pratt plans to use these composites widely on the F119 and F135 engines used on the F-22 and F-35 aircraft. General Electric Aircraft Engines is experimenting with using high temperature organic matrix composite structures on F414, GE90 (currently commercial use), F108, and F103 engines. Specific engine related structures being transitioned to OMCs include ducts, outer flaps, second stage stators, vanes, front frames/inlet cases, center vent tubes, flow bulkheads, air valves, and fan cases.