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Strain Measurement System for Operation in Extreme Environments


OBJECTIVE: Develop robust deployable strain gage system to interrogate strain in extreme thermal (minimum 1600 degrees F), acoustic (~165 dB) and dynamic frequency loading conditions. DESCRIPTION: The U.S. Air Force has a critical need for robust sensor technologies applicable to structural response strain measurements in extreme and harsh environments. This sensor technology is vital for the verification of new analytical methods and the validation of advanced structural concepts and technologies with relevance to the Air Force"s Prompt Global Strike and Response Space Access initiatives. Air Force Research Laboratory (AFRL) testing has shown traditional resistive strain gages fail due to the extreme test conditions and at best yield erroneous data due to disproportionately large thermal response and instability of the gage material. In addition, resistive gages have poor repeatability and hysteresis due to thermal aging. Several sensor technologies that have shown promise for accuracy and survivability in the extreme temperature conditions of hypersonic flight are the Extrinsic Fabry-Perot Interferometer (EFPI) optical sensor, the Fiber-Bragg Grating (FBG) optical sensor and the optical backscatter reflectometer (OBR) sensor. The goal of this effort would be to develop a hardened gage, appropriate sensor to signal conditioning interconnects and necessary signal conditioning that can evaluate both static and dynamic strains in a high-temperature environment under static and dynamic loads. It is important to note that there are several commercial strain sensing technologies available, capable of dynamic strain measurement within such an environment. However, no measurement technology is available to accurately interrogate static strain within such an extreme environment. The final result of the effort would produce a system that 1) can provide accurate static strain measurements up to 20,000 m/m from combined thermal and static load at temperatures of 1600 degrees F or greater, 2) can provide accurate strain measurement data while subjected to high acoustic loading (165 dB overall sound pressure level), 3) can provide accurate dynamic strain measurement under dynamic loading (0 to 1 KHz) equivalent to +/- 250 m/m, 4) can provide accurate strain measurement data in any combination of the aforementioned loading within 10-percent error, and 5) can provide 0 to 10 volts direct current (VDC) data acquisition (DAQ) analog output signal, proportional to strain measurement. PHASE I: 1) Demonstrate and document the aforementioned strain system for application in extreme environments, 2) develop a sound technical approach to overcome the shortfalls of the system or propose an alternative technology that meets the performance criteria, and 3) perform experiments to independently validate at minimum thermal and if possible acoustic, and dynamic solutions. PHASE II: Develop prototype strain system that can operate within the combined thermal static/dynamic loading conditions experienced in a hypersonic flight environment. Show statistical data supporting the durability and accuracy of developed system, appropriate for a TRL 4 designation. The prototype must be suitable (small package, non-invasive) for installation on high-temperature metallics and non-metallic composite aerospace structures. PHASE III: MILITARY APPLICATION: This technology would be used in the structures testing of current and future U.S. Air Force hypersonic aerospace vehicles. COMMERCIAL APPLICATION: This technology is applicable to the validation of commercial space vehicles, manned and unmanned, and advanced engine materials. REFERENCES: 1. Anthony Piazza,"High-Temperature Sensor Applications for Ground-Testing Of C-17 Engine,"NASA Dryden Research Facility. 2. Characterization of a FBG strain gage array embedded in composite structure, Yu Fan, Mojtaba Kahrizi, Electrical and Computer Engineering, Concordia University, Montreal, Que., Canada. 3. Implementation of EFPI-based Optical-fiber Sensor Instrumentation for the NDE of Concrete Structures, Marten de Vries, Vivek Arya/Scott Meller, Sami F. Masari and Richard O. Claus, Fiber and Electra-Optics Research Center, Bradley Department of Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, Department of Civil Engineering, University of Southern California, Los Angeles, CA.
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