Defect detection in steel materials using sensors based on fiber Bragg gratings

The article presents the possibilities of detecting defects in steel material using the fiber Bragg gratings (FBG). Measurement of sensitivity to force change is ensured by shifting the FBG. Steel samples were used for the tests: one standard sample and the others were incised. The incisions were at right angles and sharp to the axis of the fiber. The FBG was glued to the sample along its entire length and then lengthened by force. The transmission spectrum was being obtained on the Optical Spectrum Analyzer (OSA). It was used to determine the processing characteristics: the main minimum on the transmission characteristics and the full width at half maximum (FWHM) depending on the force transferred. On the first characteristic, the quantity of incisions can be detected (for a larger amount of incisions the main minimum changes significantly), and on the second characteristic, both the quantity of incisions (the greater the number of incisions the FWHM change is greater) and the approximate angle of incision relative to the fiber axis, FWHM decreased during increasing forces in the case of a right angle, while it increased in the case of an acute angle.