Low-cycle fatigue of welded structures made from domestic and imported materials

In various branches of modern engineering, corrosion-resistant steels and titanium alloys are widely used as structural materials. At the same time, it is possible to connect parts made from domestic and imported alloys using automatic argon-arc electric welding, which leads to the formation of a material with unexplored properties in the weld. Welded joints are stress concentrators and currently there is no information about low-cycle fatigue of welded joints obtained by fusing domestic and imported materials. In the course of the research, the modes of welding and heat treatment of butt welded joints obtained from sheet titanium alloys and corrosion-resistant steel of domestic and foreign production have been developed. Resource tests for low-cycle fatigue of samples of welded joints were carried out. Tests on low-cycle fatigue were carried out on the upgraded testing machine UMM-10 with repeated static stretching with an asymmetry factor of +0.1 and at a frequency of 0.6–0.8 Hz. The maximum tensile stress was 80% of the temporary tensile strength of the weakest alloy in the pair. The main stress axis from external loading in all cases was perpendicular to the weld. The tests were carried out until the destruction of the sample. As a result of research, it was established that all welded joints were destroyed along the fusion line, which is explained by the simultaneous action of geometric and structural stress concentrators. In this case, the destruction of the samples, as a rule, began near the seam from the side of the weakest alloy in the pair. It was also established that the use of temperatures of incomplete annealing in comparison with the full one allows to increase the cyclic durability for welded joints of titanium alloys by 1.3–2 times. From the results of comparative tests of samples of corrosion-resistant steels, it follows that domestic and imported steels, as well as their welded joints, have similar properties, both in strength and in re-static durability