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Response of an embedded distributed optical fiber sensor to directed energy and applied strain

In this research, distributed sensing based on Rayleigh scattering is used to measure temperature and strain in a composite panel during a high energy laser strike. The ultimate goal is to rapidly detect a laser strike by sensing the localized, rapid temperature rise caused when directed energy is incident on the surface of a composite structure. A secondary goal is to determine if the thermal response can be detected even in the presence of applied strain. Initial results will be discussed for composite structures comprised of carbon fiber/epoxy of various thicknesses using embedded distributed optical fiber sensors (DOFS) to rapidly detect temperature changes greater than 1000° on the surface or between plies of the composite. Measurements of the temporal and spatial response are taken at rates greater than 20Hz with sub-millimeter resolution. An infrared camera is used to validate the temperature measurements obtained using DOFS. In addition, since DOFS respond to strain as well as to temperature, any strain in the composite as a result of mechanical loading is coupled into the embedded fiber and is also detected by the sensor. Initial measurements are taken to demonstrate the simultaneous response to both temperature and strain and to characterize the typical strain that results. A DOFS-based sensing architecture can then be designed to mitigate the mechanical response of the sensor, allowing for isolation and rapid detection of the thermal response when high energy radiation is incident on the composite surface.