PSI - Issue 37

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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situations where the usage of higher resolution interferometric methods, such as Electronic Speckle Pattern Interferometry, can be interesting (Odintsev, 2021; Rickert and Suominen, 2017). However, the measurement of displacements with optical methods at such high resolution is usually limited by assembly and vibration issues. ESPI in particular requires very stable conditions due to its very high sensitivity, which usually requires its assembly on an optical table. The main objective of this work was to develop a portable testing machine that could be used with interferometric methods, namely ESPI, for assembly in INEGI’s optical tables inside a custom dark chamber with limited volume. It should also be capable of reaching a maximum load of approximately 20 kN and a velocity of 240 mm/min.

Nomenclature BLDC Brushless dc (motor) DAQ Data acquisition ESPI

Electronic speckle pattern interferometry

GUI MT

Graphical User Interface Middle tension (specimen)

Displacement in the X-axis direction Displacement in the Y-axis direction Displacement in the Z-axis direction

u v

w

Laser wavelength

λ

Angle between the camera and the beams for axis i Phase measurement for the i measurement direction

α i φ i

1.1. Electronic speckle pattern interferometry As previously mentioned, ESPI is an interferometric full-field method that can be used for displacement measurement with very high resolution, where around a twentieth of the laser wavelength is common (Creath, 1985; Grediac and Hild, 2012) . INEGI’s 3D setup (Sousa et al., 2019), built using fiber optics and represented schematically in Fig. 1, uses five different beams, all created from the same laser source to create two in-plane and one out-of-plane ESPI setups, which can be combined to perform 3D measurements, while also being able to provide X, Y, and Z measurements independently.