PSI - Issue 5

Pedro J. Sousa et al. / Procedia Structural Integrity 5 (2017) 1253–1259 Pedro J. Sousa et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 4. Z-direction displacements (W) obtained using VIC-3D for (a) approximately 600 rpm; (b) approximately 1200 rpm.

It should be noted that there is correlation loss in the blade’s tip, more significant at higher speeds. This is due to two factors: depth-of-field and motion blur. The big deformations that the blade experiences cause the tip to go out of focus due to a limited depth-of-field. On the other hand, the high velocity of the tip compared to the used shutter speed causes motion blur, more significant at higher speeds and nearer to the tip.

3.1. Shape Analysis

The obtained displacements and shape data were exported to MATLAB in order to be able to further analyze it. This allowed filling the holes in the data with interpolated values, obtaining a smooth shape. Fig. 5 shows the reference shape in green and the deformed shape that matches Fig. 4b in red. It is clear that there are significant differences. However, it should be noted that these shapes are not placed with the same exact orientation in space, therefore having significant rigid body displacements between them. In order to be able to fully compare these shapes, they were exported as STL files.

Fig. 5. Shape differences between the reference (green) and deformed (red) states as seen in MATLAB.

These files were imported into point-cloud comparison software, as it enables the manual matching of the surfaces on the left side and subsequent calculation of the differences, the result of which is shown in Fig. 6. It is possible to see that the manually matched area is shown in red, meaning that it has low differences while the tip is shown in blue, with bigger differences, in the order of 3 mm.