PSI - Issue 25

Tiago Bento et al. / Procedia Structural Integrity 25 (2020) 234–245 Tiago Bento/ Structural Integrity Procedia 00 (2019) 000 – 000

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Each fiber that was connected to the interrogator has a characteristic central wavelength dependent only on the measurand. The FBG sensors used have a 5 mm long grating. This grating size was chosen as a shorter grating could be less affected by the gradients expected in this process. The sensors have a maximum microstrain measuring value of +1250 and minimum of -1250 . To process the data emitted back to the interrogator, the machine was connected to a laptop via the software DynamicMONITOR . The function applied in the measurements to define the correlation between wavelength shift, , and the engineering values. = − (2) Where WL stands for wavelength and CWL for central wavelength. And in this case, since it was intended to measure strain: STRAIN = x × 1 (3) 1 [µ / ] is the first order sensitivity and its value is labeled to be different for each fiber. 3.4. Joint geometry The joint geometry employed in this study Fig. 2 aim to mimic structural details while simplifying as much as possible to aid in the testing and analysis.

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Fig. 2. Smart joints' plates technical drawings: Lap joint specimen. All dimensions in [mm].

The joint resulted from welding of 2 mm thick plates. After the geometry was tested the next step was to develop T-joints in which it would also be possible to incorporate the monitoring system, Fig. 3.

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Fig. 3. T-joint geometry for the bending tests. All dimensions in [mm].

3.5. Experimental procedure

Firstly, the surfaces were sanded to increase their roughness, and remove the weak oxide layer. To accommodate the fibers a 0.5 mm deep channel with a 0.5 mm radius was milled in parallel with the advancing side of the weld. The