OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 friction, but also its changes, and, besides, the equipment sensitivity to such changes should be sufficiently high. In this case, special attention should be paid to reducing the complexity of measurements. The energy method can be used to study energy dissipation in such materials for which, by appropriate choice of the chemical composition and heat treatment, it is possible to obtain samples possessing practically the same specific gravity and elastic properties, but having a large difference in the ability to dissipate energy during oscillations. This method requires the amplitude registration of the steady-state oscillations of the sample, which presents significant difficulties under production conditions [1]. The relative energy dissipation in the sample material under study during its oscillations is calculated according to the measurement data on a special installation. The use of the dynamic hysteresis loop method is impractical due to the low equipment sensitivity to dynamic deformations. The resonance curve method is used at low deformation levels, when the irreversible losses are small and the oscillatory system can be considered almost linear [2–5]. The application of this method is considered for any nonlinearity of the amplitude dependence of energy dissipation in work [6]. The method sensitivity to internal friction changes is very low with a high quality factor of the system, which does not allow using this method to detect defects in a welded joint. It is also impossible to use the dependence of the system resonant frequency on the level of irreversible energy losses in the material of the elastic element, since the change in the resonant frequency will be more affected by deviations in the sample dimensions than the defect presence in the weld. Nowadays only ultrasonic testing, as a non-destructive method, is used for testing butt joints obtained by pressure welding. At the same time, the testing results are greatly influenced by the heterogeneity of the internal structure; lightly oxidized lacks of welding penetration are not detected. It can be detected only in the presence of other defects [5]. Joints of dissimilar materials are not generally controlled by ultrasound [16]. Therefore, the development of non-destructive methods for testing such joints is very important. In the given paper the internal friction is determined by the method of the static hysteresis loop of the sample. The use of the static hysteresis loop method allows determining the energy dissipation almost directly in the weld. To obtain positive results, sensitive devices [7, 8] can be used to record small displacements. The measurement of energy dissipation by the static hysteresis loop method is carried out in this case when the welded joint is loaded with an alternating torque. The efficiency of joints depends on its strength, rigidity and damping capacity. The presence of lack of welding penetration in a joint increases energy dissipation and reduces strength. Despite the widespread use of butt welding by pressure, there are no reliable methods for detecting the main defect of these joints, that is, lightly oxidized lacks of welding penetration. The aim of the study is to create a procedure for testing the quality of a welded joint in metals and alloys, which will be a quick and simple alternative to the known methods of non-destructive testing, by measuring the energy dissipation in the sample weld using the static hysteresis loop method. Research Methodology To conduct the research, samples were obtained on the MF-327 machine by friction welding and on the MCP-30 machine by butt welding. Friction welding and butt welding were chosen as the most widely used in industry, and also because the features of joints obtained by pressure butt welding are most fully combined in joints obtained by these types of welding [9-10]. The research was carried out on joints of similar steels (steel 45* + steel 45) and dissimilar ones (steel 45 + steel R6M5**). The choice of sample materials is due to its general industrial application. Welding modes for blanks with a diameter of 25 mm are given in Table 1 for joints steel 45 + steel 45 and steel 45 + steel R6M5 obtained by resistance welding. The heating time for blanks made of similar steels varied within 15 seconds, while the heating time for blanks made of dissimilar steels was increased to 25 seconds. * quality structural steel; ~ 0.45 % of carbon. ** high-speed steel; ~ 6% of tungsten, ~ 5 % of molybdenum.
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