Two-frame phase-shifting interferometry for retrieval of smooth surface and its displacements

A new two-frame interferometric method with a blind phase shift of a reference wave is proposed for the reconstruction of smooth surface relief areas. In this method, a correlation approach based on the determination of correlation coefficient between intensity distributions of two interferograms is applied for the phase shift extraction. An algorithm for this method realization is developed and its performance is verified on test surfaces. An experimental setup containing a Twiman–Green interferometer was used in the reconstruction of smooth surfaces of metal specimens using the developed algorithm. Surface displacement phase fields were generated in case of a CT-notched specimen made of an aluminum alloy by the interactive procedure of element stitching of two surface reliefs and subtracting the surface relief after cyclic loading from the initial one. The received surface displacement fields allow us to determine the studied specimen fatigue process zone (FPZ) and FPZ size.

Research highlights
► The blind phase-shifting technique is realized through the use of the Twiman–Green interferometer.
► The blind phase shift is extracted from the correlation coefficient between interferograms.
► Two interferograms and reference and object waves allow the retrieval of the smooth surface.
► The surface of a fatigued CT-notched aluminum alloy specimen is reconstructed.
► Surface displacement is calculated in case of the determination of the fatigue process zone size.