PSI - Issue 33

6

Author name / Structural Integrity Procedia 00 (2019) 000–000

V.P. Matveenko et al. / Procedia Structural Integrity 33 (2021) 925–932

930

Fig. 6. (a) The three-point bending scheme of the sample with optical fibers embedded in the tension and compression zones; (b) Strain distribution measured by embedded DFOS in the tension and compression zones.

The results of measurements with distributed fiber-optic sensors embedded into a cement sample presented in this chapter demonstrate the possibility of using distributed FOS to register strains of engineering structures. Measurement systems built on the basis of this type of sensors allow distributed measurements with a high degree of accuracy and high spatial resolution of measurement points using standard telecommunication optical fibers. It is also worth noting the high sensitivity of the investigated measuring system, and, consequently, the possibility of measuring low levels of strain change. 3. Sensitivity of embedded DFOS to defects in the cement sample One of the important applications of embedded FOS is not only to measure the strain state of the structure in the healthy state under operational loads, but also to register the appearance and growth of defects. In order to assess the sensitivity of the embedded distributed FOS to the defect occurrence, experiments were carried out on loading a cement sample according to the three-point bending scheme described in the previous chapter. In this case, a defect was introduced into the sample in the form of a cut out (see Fig. 7a) centrally located along the length of the sample, the depth of which increased at each step of the experiment from 5 mm to 15 mm. Assessment of the redistribution of the stress-strain state of the sample in the presence of the considered defect was carried out using the finite element method, (see Fig. 7b) and a comparative analysis of the strains measured with the help of the embedded distributed FOS and the results of numerical modeling was carried out.

Fig. 7. (a) Cement sample with cut out defect; (b) Strain field in the vicinity of the defect.

Fig. 8 shows the strain distributions obtained using distributed fiber-optic sensors at the same load level and different depths of the considered defect (5, 9, 12, 15 mm). The results of numerical simulations are also given for the sizes of defects corresponding to the experiment.