Uncertainty evaluation of out-of-plane displacements measured by electronic speckle-pattern interferometry (ESPI)

Electronic speckle-pattern interferometry (ESPI) is a whole-field optical technique used to generate phase fringe patterns modulo 2 pi that allow the measurement of the displacement fields induced on a specimen by mechanical deformation. We measured by ESPI the out-of-plane displacements induced on a specimen subjected to uniaxial tensile load. Our displacement measurements were influenced by optical noise and external vibration as well as by errors in the phase measuring technique and in the determination of the interferometer sensitivity. In this paper, the influences of these errors are characterized and compared with other systematic effects through an uncertainty analysis. We evaluated the uncertainty of the sensitivity vector components of the interferometer as well as the uncertainties associated with our measurements of the phase and the displacement. According to international recommendations, we carried out the uncertainty evaluations by using Monte Carlo based computer simulations. We found that the out-of-plane displacement uncertainty depends strongly on eventual alignment errors in the optical set-up.