An aluminum embedded fiber Bragg grating (FBG) sensor configuration for a decoupled temperature and strain measurement was proposed and demonstrated. This configuration consists of a three-point regenerated FBG (RFBG) sensor array with a distance of 8 mm in one fiber. One RFBG was in direct contact with the aluminum, whereas the other RFBGs were protected from the aluminum by a steel capillary. The RFBG in contact with the aluminum was influenced by temperature and strain, and the other RFBGs only by temperature. The casting mold used here had a second symmetric arm used for an additional temperature reference measurement with three RFBGs in one capillary. Two casting experiments with this configuration were made, and decoupled temperature and strain measurements based on one sensing fiber were demonstrated. The temperature values in the strain sensing fiber showed good agreement with the reference temperatures in the second casting arm. Thereby, it could be demonstrated that one fiber was sufficient for both temperature and strain measurement and that the temperature compensation for the strain sensor was successful. This is a significant step towards the application of smart casts.
The temperature distribution during a metal casting process is important because it influences structural properties and residual stresses of the casted part. In this paper, we report on multipoint temperature monitoring based on a regenerated fiber Bragg grating (RFBG) array during a copper casting process, with a maximum temperature exceeding 1100°C. A temperature calibration function up to 800°C was obtained experimentally and was linearly extended to 1200°C. According to the experimental results, the temperature information from an RFBG temperature sensor agreed well with that from a thermocouple that was located close to the respective RFBG sensor element, even at temperatures above 1100°C. With the RFBG temperature sensor array in a single fiber, the temperature distribution and its temporal development were obtained, which can be used to better understand the copper casting process and improve the casting mold design.
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