Shutkevych O. Determination of residual stresses using high-density current impulses and laser interferometry

The dissertation is dedicated to solving a scientific and technical problem of residual stress determination using high-density current pulse and laser interferometry for relaxation. It explores the influence of electroplastic effect on local stress relaxation. The study involves both experimental and theoretical investigations on the impact of high-density current pulse on local stress relaxation. It also investigates the influence of electrode system parameters on local stress relaxation. Improvements were made to the pulse-type electrode system, and equipment was developed for electrode positioning in relation to the test sample. During experimental research, thermal imaging measurements of the temperature field at the contact point between the electrode and the surface of the test specimen were conducted. Software for processing speckle patterns and shearograms was enhanced. A mathematical model was developed to assess the impact of shear shift on the derivative distribution in stressed material after the application of a current pulse. Experiments were carried out to compare stress determination results on a real welded joint using the hole-drilling method and the high-density current pulse introduction. Object of research – the non-destructive determination of residual stresses using high-density current pulses and laser interferometry methods for their relaxation. Subject of research – the process of residual stress relaxation resulting from the electroplastic effect, the registration of displacements and deformations in the vicinity of the introduction of high-density current pulses. The purpose of the work – develop a device and technology for the non-destructive determination of residual stresses in welded joints, based on the use of high-density current pulses in combination with laser interferometry methods. Scientific novelty includes the following provisions: 1. Scientific principles have been developed for the method of determining residual welding stresses using the electroplastic effect in combination with shearography and speckle interferometry methods. 2. The application of the electroplastic effect for local stress relaxation and its use in determining residual stresses have further advanced. 3. A methodology for calculating residual stresses based on deformation and displacement data around the site of high-density current pulse introduction for local stress relaxation has been developed. 4. A comprehensive approach for determining the optimal parameters of the electrode system used for introducing high-density current pulses and for adjusting measurement systems has been proposed. 5. A mathematical model for the influence of shear shift on the distribution of derivatives in stressed material after the introduction of high-density current pulses into the stressed material has been developed. Practical significance of the obtained results. In summary, the practical value of this work lies in its ability to enhance our understanding of stress relaxation processes and to offer practical guidance for choosing the right parameters and settings in non-destructive testing procedures. These insights can lead to more accurate and effective measurements, ultimately benefiting industries and research fields where residual stress determination is critical. The practical value of this work is as follows: 1. Improved speckle interferometry and shearography instruments for measuring displacements and deformations in a region with a diameter of up to 5 mm, which allowed for more accurate experimental results and reduced the time required for experiments. 2. Developed equipment for electrode fixation and precise positioning relative to the test specimen with an accuracy of up to 0.5 mm. 3. Developed a mathematical model for the influence of shear shift on the distribution of derivatives in stressed material after the introduction of high-density current pulses. This model can be used for further research and applications. 4. Modernized software for processing speckle patterns and shearograms, reducing the time needed for processing experimental results. 5. The results of both theoretical and experimental research have led to the development of a non-destructive technology for determining residual stresses based on the use of high-density current pulses and laser interferometry.