PSI - Issue 37

V.P. Matveenko et al. / Procedia Structural Integrity 37 (2022) 508–516 Matveenko V.P., Kosheleva N.A., Serovaev G.S./ Structural Integrity Procedia 00 (2021) 000 – 000

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moment of pouring, and 6 − is the spectrum of the finished sample. Analyzing the spectra, it can be noted that they have one pronounced peak and retained their shape. 2.2. Embedment of FOS into an cement sample The cement mixture is the main binder in the manufacturing of concrete products and structures. The properties of the cement mixture and their change in the future determine the mechanical properties of concrete. FOS based on Bragg gratings, embedded into a cement sample, provide new experimental information on the mechanical properties of the material. The evolution of the readings of the embedded FOSs based on FBG makes it possible to better study the processes occurring during the cement formation. It should be noted that in this work, the embedded FOS did not have additional protection, except for the standard polyimide coating. The mold shown in Fig. 1a was used to create a sample. Similar to the epoxy sample, protective tubes were embedded into the side holes to ensure the integrity of the fiber-optic outputs. To create a cement sample, Portland cement 400 and river sand were used in a ratio of 1:5. Continuous recording of readings from embedded FOSs with a frequency of 1 Hz was carried out for 277 hours after pouring the sample. Fig. 3 shows resonant wavelength shift and FBG spectra obtained at different points in time: 1 − spectrum at the time of pouring, and 3 − spectrum of the sample after 8 days. Analyzing the spectra, it can be noted that they have retained their shape and have one clear peak. The sample is shown in Fig. 4.

Fig. 3. Evolution of FOS readings and reflected spectra at different points in time in a cement sample.

Fig. 4. Cement sample with embedded FOS

2.3. Embedment of FOS in liquid plastic Products made of liquid plastics have high strength and low weight characteristics. A two-part cold cure polyurethane mixture, which cures at room temperature, was used to create the plastic specimen according to the manufacturer's recommended ratio of the main component to the hardener of 100 to 60. During the 19 hours after pouring the mixture, data acquisition from FOSs was carried out. Fig. 5 shows resonant wavelength shift of embedded FBG and reflected spectra corresponding to separate time points, indicated by numbers, where 1 − is the spectrum at the time of pouring, and 6 − the spectrum after 19 hours of curing.