PSI - Issue 33

Vitor E.L. Paiva et al. / Procedia Structural Integrity 33 (2021) 159–170 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The DIC experimental test setup consisted of a stereoscopic vision system composed of two 5 megapixel CCD cameras (Point Gray GRAS-50S5M) mounted on a tripod. The cameras were fitted with adjustable focal length lenses (Tamron A031 AF28-200mm F / 3.8-5.6). A lighting system was used in order to obtain homogeneous illumination in the region of the specimen to be analyzed. Before testing, the stereoscopic system was calibrated to allow for 3D DIC analysis in order to retrieve three-dimensional strains and displacements on the surface of the dented pipe. The 3D-DIC system used in this study was the commercially available VIC-3D model developed by Correlated Solutions et al. (2019). The experimental tests were carried out in the laboratory prepared for such tests in the facilities of the CTDUT (Center of Technology in Pipelines). The experimental setup is shown in Figure 2.

Fig. 2. Experimental setup used for in-lab (in-air) investigation.

Fiber optic Bragg strain gage sensors were bonded to the hot-spot locations of the specimens to collect strain information during testing. A cyanoacrylate-based adhesive was used. Each fiber DTG-LBL-1550-F Ormocer coating (Fiber Bragg Gage Sensors FBGS©) contained two Bragg grating sensors (placed 80mm from each other) with gage length equal to 8mm and distinct wavelengths (1514nm and 1524nm) allowing for multiplexing the strain signal. The fiber optic conditioning equipment, Micron Optic – si255-16-ST/160, operated with two channels at an acquisition frequency equal to 1000 Hz. Figure 3 depicts two fibers with four gages mounted along the circumferential direction in the dent region of a tested specimen. The Bragg sensors are highlighted by circles in the Figure 3.

Fig. 3. Location of four Bragg sensors belonging to two optical fibers mounted in the dent region of a tested specimen..