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Pitting Corrosion Sensor and Tracker
Navy SBIR 2011.2 - Topic N112-120 NAVAIR - Ms. Donna Moore - [email protected] Opens: May 26, 2011 - Closes: June 29, 2011 N112-120 TITLE: Pitting Corrosion Sensor and Tracker TECHNOLOGY AREAS: Air Platform, Materials/Processes, Sensors ACQUISITION PROGRAM: F-35, Joint Strike Fighter OBJECTIVE: Develop a sensor and tracking system that will detect and track corrosion between two metallic surfaces. DESCRIPTION: Many of the corrosion inspection methods currently employed in the field to inspect magnesium housings involve disassembling the components and performing a visual inspection. The man-hour effort can be extensive, resulting in long time spans between inspections. Occasionally, the protective coatings become compromised during the disassembly process, and the damage remains undetected. As a result, the next disassembly inspection may reveal severe corrosion, failing the parts and exposing a potential safety hazard. Corroded parts that do not fail the established damage limits are blended and returned to service. Those that do fail are replaced or repaired. Repair options for holes include installing bushings; oversizing bushings; rebuilding hole walls with epoxy compounds; or simply blending the corrosion and then treating, priming, and painting the exposed metal. Repair options for flat surfaces include machining surfaces flat and installing a shim to return the surfaces to their blueprint condition, filling blended and dimpled surfaces with epoxy, or leaving the surfaces with blended divots and scooped out material. These repairs can form water entrapment or intrusion areas that result in corrosion that may fail the part at the next scheduled visual inspection. These corrosion-prone areas are normally where flight controls and gearbox mount feet attach, and the load path through these locations is critical for aircraft safety. The problem to be solved is to find a better inspection system for magnesium housings that will detect corrosion more efficiently and effectively. One way to do this is to develop an innovative sensor system consisting of sensors and a portable, handheld unit. Inspections should occur at opportune times when the aircraft is not flying, and the sensors should receive power only from the handheld unit. The sensors can be permanently attached to the portable unit or permanently mounted on the housings either in the form of gaskets between the mating surfaces or secured by the installation of structural bolts that hold the surfaces together. If the sensors are attached to the portable unit, inspection would involve the sensors being temporarily installed or swept across the corrosion-prone areas and then removed to prevent a foreign object damage safety risk. If the sensors are mounted on the housings, inspection would involve plugging the portable unit into the sensors. The sensors should detect corrosion pitting in 0.005-inch depth increments starting from 0.005-inch deep to 0.100 inch or greater. Each surface should have its baseline stored in memory for tracking and trending purposes. The sensors should identify the location of pitting within a 1.00-inch area of where the pitting is occurring. The sensors should also account for any previous repairs described above and determine if the previously blended uneven surfaces, bond-lines, or bushing-housing interfaces are developing any corrosion-induced voids. The sensors should determine the compressive loads between the surfaces to ensure that the bolts have proper preload, or they should determine the bolt preload. If the sensors will be permanently mounted on the housings, they should have a robust design to detect fretting-induced corrosion. The sensors must be capable of determining the pressure between mating surfaces within 10 percent accuracy, or they must detect bolt preload within 10 percent accuracy. If the sensors are in the form of a gasket, the sensors must be hardened to withstand 0.0015 inch of fretting movement amplitude under a steady 1,000 psi pressure for 1,000 cycles. This requirement will demonstrate the sensors� robustness and potential longevity for in-field service. If the sensors will be permanently mounted on the housings, it must be demonstrated that the corrosion conditions that cause the various depths of pitting on the magnesium should not also cause the sensors to fail. Test to corrosion failure (0.100 deep) of the sandwiched materials is required to refine the sensors, to demonstrate the ability to calibrate the corrosion depths via sensor feedback, and to validate the ability of the sensors to accurately quantify the current health state and predict the remaining useful life of the parts. PHASE I: Design, develop, and demonstrate proof-of-concept sensors and associated state awareness sensor algorithms that are capable of making corrosion activity determinations for magnesium housings and of mapping where this corrosion is occurring within 1.00 inch of accuracy. Demonstrate that the sensors can detect 2,500 psi of pressure between magnesium and aluminum mating surfaces with 20% accuracy, or that they can measure the 16,500 lbs of bolt preload that holds these surfaces together with 20% accuracy. PHASE II: Increase the corrosion pitting detection resolution to demonstrate detection of corrosion depths at 0.005 inch, 0.010 inch, 0.015 inch, 0.020 inch, etc. to 0.100 inch deep. Increase the sensors� ability to determine bolt preload by determining pressures between mating surfaces in 500 psi increments starting at 500 psi up to 2,500 psi, or by determining bolt preload in 3,000 lb increments starting at 3,000 lbs up to 18,000 lbs. The sensors must be capable of determining the pressure between mating surfaces within 10% accuracy, or they must detect bolt preload within 10% accuracy. If the sensors are in the form of a gasket, the sensors must be hardened to withstand 0.0015 inch of fretting movement amplitude under a steady 1,000-psi pressure for 1,000 cycles. This requirement will demonstrate the sensors� robustness and potential longevity for in-field service. If the sensors will be permanently mounted on the housings, it must be demonstrated that the corrosion conditions that cause the various depths of pitting on the magnesium should not also cause the sensors to fail. PHASE III: Conduct the necessary qualification testing and finalize the sensors for transition to both military and commercial applications. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The corrosion sensor system developed under this topic would significantly enhance the state of the art for commercial aviation. The technology is directly transferable to military and commercial gearbox, airframe, maritime, and many other applications. REFERENCES: 2. Park, G., Muntges, D. E. & Inman, D. J. (2000, November). Smart materials technologies for bolted-joints in civil systems. Paper presented at the 2nd Workshop on Mitigation of Earthquake Disaster by Advanced Technologies, Las Vegas, NV. Retrieved from http://www.cimss.vt.edu/pdf/Conference%20Papers/Park/C37.pdf 3. Das, S., Srivastava, A. N. & Chattopadhyay, A. (2007, March). Classification of damage signatures in composite plates using one-class SVMs. Paper presented at the 2007 IEEE Aerospace Conference, Big Sky, MT. Retrieved from http://ti.arc.nasa.gov/m/pub/archive/One-Class-SVM-Composites-IEEE-2007.pdf KEYWORDS: aircraft maintenance performance; propulsion; drive systems; corrosion; sensors; inspection
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