Study of inhomogeneous fields of residual stresses using step-by-step enlarged crack method in combination with electronic speckle pattern interferometry (ESPI)

This article covers the development of methodological issues, software, experimental equipment, and practical application of the method of sequentially increasing cracks for studying inhomogeneous high-gradient fields of residual stresses (RS) that occur in areas of structural heterogeneity in flat construction parts (e.g., welded joints). Method of electronic speckle pattern interferometry (ESPI) is used to detect the deformation response in the form of the fields of displacement of the surface of the object under study arising from formation of successively increasing crack. ESPI provide contactless registration of movements directly in a digital form with high accuracy. The scheme of a specialized interferometer is described along with the features of the procedure for registering the displacement fields arising from a stepwise increase of the crack length. A return device provided removing of the object under study out of the optical zone and then return it to the initial position after performing the necessary mechanical operations. The accuracy of the procedure for calculating RS is estimated on the basis of mathematical processing of the experimentally obtained dependences of SIF on the crack length. An example of using the developed methods, equipment and programs for studying the RS distribution in stir welding joint of the sheets of aircraft alloy 1163T with a high level of crack resistance is given.

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