Measurement of Strain Fields in Aging Aircraft Using Distributed Bragg Gratings

The primary aging mechanisms that are known to reduce the economic service life of both civilian and military aircraft are corrosion, stress corrosion cracking, and fatigue. The Air Force Scientific Advisory Board on Materials Degradation estimates thecosts of corrosion related detection and repair at between $1 and $3 billion dollars annually. An NRC study states that while preventative measures may eliminate two of the mechanisms, fatigue due to aircraft use will always be present. The nature of theproblem calls for a global strain measurement techniques to monitor the effects of widespread fatigue damage. In order to achieve this global measurement, 1000's of measurements distributed throughout the aircraft will be required. Only the techniqueoffered in this proposal has demonstrated the ability to obtain 1000's of high spatial resolution measurements on a single optical fiber. The Phase I effort will be used to tailor a prototype system to demonstrate the technology on an Air Force aircraftexperiencing both fatigue and corrosion problems. In Phase II, a robust system will be fabricated according to Air Force specifications to meet the demands of routine inspection for widespread fatigue and corrosion damage. The commercial applicationsinclude health monitoring in civil, aviation, and marine structures. The push to smart materials and structures requires monitoring of all phases of the construction process and will create a large demand for cheap sensor arrays and deployable demodulationsystems. The technology also competes with traditional foil strain gage and thermocouple technology that is well established in all areas of industry. As demodulation systems are introduced to solve measurement problems not addressed by traditionalsensors, the technology will gain acceptance by the engineering community and encroach on the traditional sensors market share.