PSI - Issue 37

Francisco Barros et al. / Procedia Structural Integrity 37 (2022) 880–887 Barros et al./ Structural Integrity Procedia 00 (2019) 000 – 000

884

5

Fig. 4. Checkerboard pattern placement on the calibration image for the 2D setup.

(a)

(b)

Fig. 5. Calibration pattern: (a) in the original image; (b) after perspective correction.

3.2. Digital image correlation

The subset matching operation was performed using an algorithm based on the discrete Fourier transform (Barros, et al., 2018), which computes the correlation peak with subpixel accuracy based on the methodology proposed by Guizar-Sicairos et al. (2008), with a resolution of 1/100 px. The displacement of each subset was modelled as a rigid translation, which is a valid approximation because the deformation of the surface is very small. Subsets were matched, at first, between camera A and camera B for the unloaded state, in a process described in the next subsection, and subsequently between the unloaded and loaded states for each camera. The final 3D positions of the points from their image coordinates were obtained for each state using the previously obtained calibration