PSI - Issue 33

V.P. Matveenko et al. / Procedia Structural Integrity 33 (2021) 925–932 Author name / Structural Integrity Procedia 00 (2019) 000–000

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undergoing tensile strain under three-point bending. In numerical modeling, the elastic modulus of cement (E = 9.2 GPa,  = 0.18) was selected according to the smallest deviation from the values of single point FOS on one of the loading steps and was subsequently set unchanged for all other calculations.

Fig. 4. (a) Strain measurements in the sample under different load levels by DFOS, FBG sensors and numerical simulations; (b) The initial registered data and processed by moving average for distributed FOS.

Fig. 5 shows the dependences of measured strain on the load for the considered options for measuring and calculating strains at the locations of single point FBG sensors. Comparison of the results showed the average difference within 6.8% between distributed and FBG sensors and 6.7% between distributed sensors and the finite element method.

Fig. 5. Dependences of measured strain on the force for DFOS, FBG sensors and numerical simulation.

In order to minimize abrupt changes in readings along the length of the measured section of the optical fiber, the data from the distributed fiber optic sensors was processed using moving average method by 10 points. The initial and averaged data for three load levels are shown in Fig. 4b. Due to the fact that the sections of the optical fiber were embedded symmetrically with respect to the neutral line of the sample it is possible to register strains both in the tension and in the compression regions under loading according to the three-point bending scheme. Fig. 6 shows the strain distribution in the corresponding sections at three levels of load, which shows the insignificant asymmetry of the tensile and compressive strains measured by the DFOS.