PSI - Issue 37

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Pedro J. Sousa et al. / Procedia Structural Integrity 37 (2022) 730–737 Sousa et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The physical implementation of the 3D ESPI setup is shown in Fig. 2, where it is possible to see that the top Y direction beam required additional fixations to ensure the necessary stability. Additionally, in order to switch between the X, Y, and Z sensitive setups, the different beams can be selected using shutters, implemented through the use of miniature servo motors, also seen in Fig. 2, that are controlled with a custom system, built around a PIC24FJ128GB202 from Microchip Technology, as shown in Fig. 3.

Fig. 2. INEGI's 3D ESPI setup.

Fig. 3. Custom shutter controller.

2. Mechanical design Regarding the mechanical design of the machine, the first step was to use the speed and force requirements (20 kN and 240 mm/min) to select a motor and the necessary couplings. The choice fell upon a QBL4208-100-04-025 BLDC motor from Trinamic, as well as a 1:70 reduction gearbox and 25 Nm coupler, the latter of which to be assembled after the gearbox’s torque increase . The main goal was to use MT (middle tension) specimens with our ESPI setup and, therefore, one of the main concerns was the alignment of the crack with the center of the ESPI's measurement area, as can be seen in Fig. 4.