Uncertainty evaluation of strain and strain rate measurements by ESPI during a tensile test

Localization of plastic strain has been studied by measuring strain and strain rate during tensile test(1). Pictures were continuously recorded during the experiment and in-plane Electronic Speckle Pattern Interferometry (ESPI) pictures were generated afterwards, by subtracting couples of images. A square grid of 3 nun separation was drawn on the specimen to determine the true stress-true strain curve, while fringe patterns gave an access to relative displacements. Strain, average strain and strain rate were deduced. An uncertainty evaluation on these parameters was carried out applying the so-called law of propagation of uncertainties (ISO 07-020(2)).