Abstract
Our purpose is the direct strain measurement from the interrogation of a crossed grating marked on the surface of a specimen. The observation of the object through a master grid (as in moiré method) is replaced by a direct characterization of the pattern using a Fourier transform. This gives direct access to the modification of the pitches which leads to quantification of the strain without the intermediary of a fringe pattern. The comparison between the undeformed and deformed states allows the determination of the magnitude and orientation of principal strains and of the local rigid-body rotation. We describe three analysis techniques, one using the diffraction phenomenon, another utilizing a numerical spectral evaluation and third combining diffraction and phase-shifting procedure. These grid interrogations have different domains of application and a suitable choice of these analysis techniques allows a very large measurement range (10−5 to high strain according to the grating resistance).
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Dupre, J.C., Cottron, M. & Lagarde, A. Grating interrogations: from small to large strain measurement. Experimental Mechanics 35, 153–158 (1995). https://doi.org/10.1007/BF02326474
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DOI: https://doi.org/10.1007/BF02326474