Abstract
Strain sensor designs and strain measurements based on single-crystal sapphire fibers with inscribed first-order fiber Bragg gratings for applications up to 600 °C are presented. We report on all the details of two different sensor designs; for instance, we show that the resolution of multimode sapphire fiber Bragg grating (SFBG) strain sensors is about $\Delta{l/l}=10^{-5}$ (10 $\mu\text{strain}$ ), which is comparable with state-of-the-art high-temperature sensors. We apply our sensors for the determination of the thermal expansion coefficients of high-temperature steel alloys, showing a good match to known values. Hence, we believe that SFBG sensors may represent a promising alternative to currently used non-optic-based strain-detecting devices.
Highlights
Higher operation temperatures in power plants [1] or gas turbines [2] allow an increase in the efficiency of such infrastructures and, a reduction of CO2 emissions
Mechanical strain at high temperatures leads to material fatigue, and structural health monitoring (SHM) with adapted new types of sensors [4], [5] is a key issue for a long-term safe operation in such a crucial environment
Mihailov et al showed in the first publication on sapphire FBG as strain sensor [18] that the response of the Bragg wavelength shift on strain is 1.4 pm=strain, and they calculated for the coefficient of the photo elastic interaction (1) p 1⁄4 0:13 [18]
Summary
Higher operation temperatures in power plants [1] or gas turbines [2] allow an increase in the efficiency of such infrastructures and, a reduction of CO2 emissions. Strain gauges based on Pt-W alloys as sensing elements for application at higher temperatures are available [6]. This clearly emphasizes that developing strain gauges for long term high temperature application is of key interest in many applications Due to their flexibility, fiber optic strain sensors are of great importance and are commercial in various implementations [7]–[9]. Fiber Bragg sensors provide a unique combination of high sensitivity and high dynamic range They are of particular interest for industrial application since they can be applied in harsh environments [10] such as high temperature, radiation, Vol 8, No 3, June 2016. We will discuss the performance of SFBG for strain sensing and show, as an example, an application of our sensor for measuring the thermal expansion of various steels at high temperature
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