Direct Strain and Slope and Slope Measurement Using 2D DSPSI
Large variety of optical full-field measurement techniques are being developed and applied to solve mechanical problems. Since each technique possesses its own merits, it is important to know the capabilities and limitations of such techniques. Among these optical full-field methods, interferometry techniques take an important place. They are based on illumination with coherent light (laser). In shearing interferometry the difference of the out of-plane displacement in two neighboring object points is directly measured. Since object displacement does not result in interferometry fringes, the method is suited for localization of strain concentrations and is indeed used in industry for this purpose. DSPSI possesses the advantage over conventional out-of-plane displacement-sensitive interferometry, that only a single difference of the unwrapped phase map is required to obtain flexural strains, thereby relieving problems with noise and reduction in the field of view. A first work in this domain (DSPSI)  was made in 1973, later recent studies emerged to provide a quantitative system of measurements . This work aims to present the results of strain and slope measurements using digital speckle pattern shearing interferometry (DSPSI).
Maher Soueidan, Mohamad Roumié and Pierre Masri
W. Dandach et al., "Direct Strain and Slope and Slope Measurement Using 2D DSPSI", Advanced Materials Research, Vol. 324, pp. 384-387, 2011