ESPI is classically used in high resolution measurements of deformation, but ESPI can also be sued for contouring of surface even with discontinuities. Furthermore, measurements of both shape and deformation had been carried out. It has been shown that performing both measurements is necessary to obtain the actual strain information at the specimen topography, and the development of such techniques was presented as an alternative to other strain measurement methods, among who wire resistance strain gauges is the most popular one. But, despite its reliability and popularity, the strain gauges technique has some disadvantages. Its set- up is very time-consuming: in order to assure tight contact between gauge and measured surface, one has to take care about the specimen surface cleanliness and roughness and the gluing step takes hours; mounting the electric circuit also request for time and work due to the small voltage signs, demanding high sensible signal amplifiers and bridge-circuit units able to perform compensation of temperature variation and protection from noise. Beside s that once the given strain information result from the integration over the whole area covered by the gauges, this technique gives no lateral resolution.
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