Nondestructive testing of composite and metallic pipes by the method of electronic shearography
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NONDESTRUCTIVE TESTING OF COMPOSITE AND METALLIC PIPES BY THE METHOD OF ELECTRONIC SHEAROGRAPHY L. M. Lobanov, V. A. Pivtorak, I. V. Kyyanets’, and O. M. Savyts’ka A method for nondestructive testing of the quality of structures based on the application of electronic shearography is proposed. We present results of monitoring of the elements of pipes produced by welding and gluing. The presented results of investigations show that the developed technology can be applied under the conditions of manufacturing.
The methods of laser interferometry, i.e., of the optical holography, electronic speckle interferometry, and shearography, open broad possibilities for the nondestructive testing of the quality of structures [1–3]. Among these methods, the method of electronic shearography proves to be especially promising. It has serious advantages over the other methods. Thus, it is quite clear, contactless, insensitive to the influence of the environment upon the object of investigations, and enables one to test fairly large objects of complex geometric shapes in real time and collect data on the surface deformation of the object. According to the method of electronic shearography, the surface of an object is completely or partially illuminated with laser beams. The radiation scattered by the surface comes to a shear element located in front of the lens of a CCD camera and splitting its aperture into halves (Fig. 1). As a result, two shifted images of the object A′ – B′ and A′′ – B′′ are formed in the recording plane. The apex angle γ of the shear element specifies the shear shift between the images. As the shear element, one can use, e.g., a glass optical wedge with an angle of 0.75°. As a result of the interference of light waves, we observe the formation of chaotic microinterference speckle patterns stored with the help of the CCD camera in the computer. The microinterference speckle patterns written for two states of the object (prior to and after loading) are compared by using a computer program and processed to get the patterns of macrointerference fringes, i.e., shearograms. The optical scheme of the shearographic method is based on the following assumptions: 1. The sizes of objects or their regions are much smaller than the distance between the laser and the investigated surface. 2. The shear module is located perpendicularly to the surface of the object, i.e., on the z-axis (Fig. 1). 3. The angle θ between the directions of observation and illumination lies in the coordinate plane. As a result of the analysis of the optical scheme of shearographic interferometer, we established basic dependences of the relative phase difference ∆ ϕ on the parameters of the optical scheme and the derivatives of the displacements u, v, and w. The phase difference ∆ ϕ caused by the shear shift along the Ox- and Oy-axes is given by the formulas [4]: Paton Institute for Electric Welding, Ukrainian Academy of Sciences, Kyiv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 4, pp. 66–70, July–August, 2007. Original artic
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