Double wavelength speckle interferometer for the research of static deformations of gas turbine engine parts

Two coherent radiation sources with the wavelength of 532 nm and 632.8 nm are used in a speckle interferometer optical arrangement with combined beams and speckle-modulated background wave. The reference beam is formed with the help of a diffuser located in front of the object under investigation. The use of two radiation sources in the optical arrangement makes it possible to increase the number of experimental points, which is necessary for improving the accuracy of measuring static displacements of the surface of the part under investigation. A diagram of normal displacements of the leading edge of a blade of the 7^th compressor stage under bending deformations has been plotted using additional experimental points. A digital still camera is used as a registering device. Two speckle-interferograms have been obtained at different wavelengths of a blade of the 9-th compressor stage under torsion with the use of the long-wavelength speckle interferometer. It was proposed to use a pattern that represents the product of these two speckle-interferograms in order to determine the zero band. A method of determining the zero band under torsion has been developed for the case when the part of the blade surface adjoining the attaching point is not available for observation and several shadow bands fall on the attaching point at once. This methodology has been tested for zero band determination on a speckle-interferogram obtained under static torsion of a blade of the 9-th compressor stage.