Peculiarities of formation and processing of surface interferograms according to Twyman-Green scheme in non-destructive testing

Abstract

The goal of the work is to ensure the maximum accuracy of reconstruction of relief and de-formation displacement fields of structural element surface by the interferometric method. The authors successfully use novel algorithms for the processing of surface interferograms as well as the interferometers that follow the Twyman-Green scheme in order to implement such opti-cal testing of the surface. The maximum precision of obtained experimental data was achieved by the use of structural additions to the optical circuit and the selection of optical elements and their settings during adjustment of the interferometer, as well as new algorithms for the selec-tion and registration of a series of interferograms, speckle interferograms and speckle surface images. The authors proposed structural additions to the interferometer scheme used in the testing of both smooth and rough surfaces, appropriate methods for calculating the parameters of optical elements and their adjustments. Examples of obtained interferograms of the surface of metals under the static and fatigue cyclic loading, speckle interferograms of the surface of metals and polymer composites under the static and dynamic loading are given. The results of processing and interpreting these interferograms confirm that the Twyman-Green interfero-meter is an effective instrument for solving the problems of fracture mechanics and deformable solids. In particular, an assessment was made of: roughness and waviness of the surface of metals; sizes of the plastic zone around the stress concentrator; deformation displacement fields of metals and composites, as well as the detection of hidden defects in them.