PSI - Issue 42

6

Valerii Matveenko et al. / Procedia Structural Integrity 42 (2022) 307–314 V.Matveenko, N.Kosheleva, G.Serovaev/ Structural Integrity Procedia 00 (2022) 000 – 000

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The periodic strain changes in the form of spikes of measured data are the strain response of the FBG to the passage of the 3D printer nozzle in the vicinity of the corresponding sensor. The main stage of the formation of technological compression strains begins after the end of the printing process, during the cooling of the sample and reaches an asymptotic value at 5.5 hours after the embedment of FOS. Figure 5 (a)-(b) shows the reflected spectra for FBG sensor s1 at various points in time: 1 , 2 , 3 – during the printing of the sample, 4 , 5 – after the end of the sample manufacturing. No change in the structure of the reflected FBG spectrum was observed.

Fig. 5. Reflected spectra of the sensor s1 at various points in time

The graph of temperature change recorded by the temperature sensor is shown in Figure 6.

Fig. 6. Temperature change registered by the embedded encapsulated FBG sensor

In the process of printing the sample, the temperature sensor recorded a periodic temperature response to the passage of a hot nozzle in the vicinity of the sensor location with a period corresponding to the period of the strain response of sensors s1, s2. Based on the readings of the temperature sensor, it can be concluded that during the printing process, the temperature of the material was close to the temperature of the heating table of the 3D printer (60 ˚ C when printing with polylactide) and may exceed this value due to the passage of a hot nozzle. Polylactide has one of the lowest glass transition temperatures among the materials used by FDM technique. Thus, it is not recommended to embed optical fiber with an acrylate coating, since the temperature limit for this coating is 60 ˚ C. Based on the measurements of distributed fiber-optic strain and temperature sensors, the distribution surfaces of these parameters along the length of the sample in time were constructed, shown in Figure 7.