PSI - Issue 79

Charoula Kousiatza et al. / Procedia Structural Integrity 79 (2026) 146–154

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bottom surface having embedded the corresponding FBG sensor being always located close to the extensometer’s knife edges. Special care was taken to prevent damaging the FBGs during samples’ installation. After mounting each test coupon and just before the initiation of the tensile test, a reference Bragg wavelength ( λ B0 ) was recorded. The crosshead travel speed was set to 5mm/min for all tensile tests.

Fig. 2. Specimen’s installation on the testing machine.

3.3. Scanning Electron Microscopy (SEM) Specimens that underwent tensile loading and subsequently fractured, were then examined under a desktop scanning electron microscope (SEM) (Phenom ProX, Thermo-Fisher Scientific, Massachusetts, USA) to assess the embedment quality of the respective optical fiber(s) within the host material. The samples were mounted on a metal stub using double-sided carbon tape and placed into the SEM vacuum chamber with a specialized charge reduction sample holder. Instrument operation and data acquisition were performed using the proprietary ProSuite PC software. 4. Results and discussion 4.1. Temperature profiles’ monitoring The temperature recordings obtained from the embedded K-type thermocouples as a function of building time are presented in Fig. 3. More specifically, in Fig. 3a, the generated temperature profiles are presented, as recorded after the first thermocouple’s placement between the building platform and the 1 st deposited layer and subsequently, after the second thermocouple’s integration at the top of the 8 th layer of the printed specimen. Based on Fig. 3a, it is evident that peak temperatures occur when the printer’s head passes directly above the embedded thermocouple, while temperature decreases as the print head travels away from the sensor’s location. Therefore, the total number of peaks recorded by the first thermocouple corresponds to the total number of the specimen’s deposited layers (n=16), while a total number of 8 peaks is recorded by the second thermocouple embedded in the middle of the structure. In addition, Fig. 3b presents the overlapped temperatures for the bottom and middle embedment positions, thus providing a direct comparison of the respective process-induced temperature profiles. The maximum temperature recorded by the second thermocouple is ~100ºC, while the respective one derived by the first thermocouple is ~108ºC, thus indicating that the built specimen’s lower layers are strongly influenced by the heated platform in addition to the molten deposited material. As the fabrication process progresses, the maximum temperatures generated within the specimen stabilize around 90ºC and minimum around 85ºC, respectively. Based on a previous study conducted by our research team, the T g of PA specimens with 0 o raster orientation was found to be approximately 52ºC (Matsika-Klossa