Abstract
Prior research has demonstrated that distributed optical fiber sensors (DOFS) based on Rayleigh scattering can be embedded in carbon fiber/epoxy composite structures to rapidly detect temperature changes approaching 1000 °C, such as would be experienced during a high energy laser strike. However, composite structures often experience mechanical strains that are also detected during DOFS interrogation. Hence, the combined temperature and strain response in the composite can interfere with rapid detection and measurement of a localized thermal impulse. In this research, initial testing has demonstrated the simultaneous response of the DOFS to both temperature and strain. An embedded DOFS network was designed and used to isolate and measure a localized thermal response of a carbon fiber/epoxy composite to a low energy laser strike under cyclic bending strain. The sensor interrogation scheme uses a simple signal processing technique to enhance the thermal response, while mitigating the strain response due to bending. While our ultimate goal is rapid detection of directed energy on the surface of the composite, the technique could be generalized to structural health monitoring of temperature sensitive components or smart structures.
Highlights
Optical fiber sensors provide several advantages for detecting temperature or strain in polymer matrix composites [1,2,3]
Though an optical fiber is fragile, it is sufficiently flexible to embed in composite structures, and optical fiber sensors respond to changes in strain or temperature quickly and with high sensitivity [4], even at very high temperatures [5,6,7]
Distributed optical fiber sensors (DOFS), DOFS based on Rayleigh scattering, can detect temperature or strain with high spatial resolution [8]
Summary
Optical fiber sensors provide several advantages for detecting temperature or strain in polymer matrix composites [1,2,3]. Distributed optical fiber sensors (DOFS), DOFS based on Rayleigh scattering, can detect temperature or strain with high spatial resolution [8]. DOFS are distributed sensors with numerous sampling points along the entire length of the fiber that can be spatially resolved using swept wavelength interferometry, with greater likelihood of detecting and locating a strike The focus of this effort was to use localized heating in the presence of applied mechanical strain to test a concept for strain cancellation in a properly configured DOFS network [13] that would mitigate the effect of bending strain on the rapid detection of a HEL strike. Test results are described when both strain and heating are present in the composite specimen, to demonstrate how the temperature response can be enhanced as the strain response is canceled
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