Development of a Laser Interferometry Method for Assessing Residual Stresses in Welded Structures

Methods for the experimental assessment of residual stresses are analyzed. A corrected classification of the methods is proposed. As a result of comparing the capabilities of the experimental methods, it is shown that mechanical methods are most suitable for assessing residual stresses in the weld zone of welded structures. Among the mechanical methods, of most interest are methods based on creating a probing hole of small diameter and depth. It is shown that the technique for measuring the displacements of surface points in the drilling zone described in GOST R (State Standard) has significant advantages over the American standard. However, the domestic regulatory document gives no recommendations on the choice of interferometer's optical scheme and does not indicate requirements for the geometric parameters of the probing hole. To increase the sensitivity of the Leith-Upatnieks optical scheme, used to measure the displacements of points on the hole edge, it is proposed to change the slope of interferometer's optical plane. The sensitivity of the method has also increased accordingly to approach the sensitivity indicators of other optical schemes. As a result of mathematical modeling in the ANSYS program, it has been proved that the flat-bottom hole recommended in the American standard can be replaced by a cone-bottomed hole, which is much easier to fabricate. Modeling and subsequent additional calculations have made it possible to establish the optimum ratio between the depth and diameter of the probing hole. It has been shown that the drilling depth can be halved compared with the requirements of the American standard. Based on the data obtained, a new DON-5TsZ interferometer has been designed and recommendations on the choice of the geometric parameters of the probing hole have been developed.