OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 Welds with different amounts of lack of welding penetration dissipate energy in different ways similarly to the shear strength of the contact. The greater lack of welding penetration, the more energy is dissipated in the weld. Firstly, this is explained by the fact that a larger number of micro irregularities are deformed in a larger contact area and a larger number of contact elements slip. Secondly, lack of welding penetration reduces the polar resisting moment of a section, and this leads to the occurrence of large shear stresses in those welds that have greater lack of welding penetration, when loading all joints with equal torque. More shear stress causes more micro displacement, resulting in more energy dissipation in the weld. The difference in the energy dissipated in welds with different values of lack of welding penetration increases with the increase in the loading amplitude. Energy dissipation connection with relative joint strength for different torque amplitudes turned out to be satisfactory (fig. 6). Lines 1, 2, 3 correspond to amplitudes of 147; 156.8; 176.4 N∙m; “○”denotes joints obtained by friction welding; “●” denotes resistance welding. The ratio of the breaking moment of the specimen to the breaking moment of the specimen from annealed steel 45 is plotted along the abscissa axis. This designation is accepted in all figures. a b Fig. 6. Relation between energy dissipation and relative strength of welded joints: a – steel 45 + steel 45; b – steel 45 + R6M5 for different torque amplitudes The dependence of the absorption coefficient on the loading amplitude (fig. 7) is similar to the dependence of energy dissipation. Lines 2, 3 are joints obtained by friction welding; 1, 4 are joints obtained by resistance welding; 5a, 5b are solid specimens of steel 45 and steel R6M5. The connection of the relative strength of joints with the weld absorption coefficient is shown in fig. 8. The designations are similar to those in fig. 6. With the increase in the loading amplitude, the rigidity of specimens made of steel 45 and steel R6M5, as well as welded specimen without lack of welding penetration, remains constant (fig. 9). Line 2 is joints obtained by friction welding; 1, 3 are joints obtained by resistance welding; 4, 5 are solid specimens of steel 45 and steel R6M5. Rigidity constancy is explained by the direct proportional dependence of the deformation on the load when loading the specimen in the elastic area. The rigidity of joints with lack of welding penetration decreases with increasing loading amplitude due to the deformation of the micro irregularities of the rough surface and the contact element sliding. In general, the amplitude dependence of the rigidity of welded joints is non-linear [2, 3, 9]. At small loading amplitudes, the rigidity of specimens made of steel 45 and steel R6M5 may turn out to be less than the rigidity of welded joints that have lack of welding penetration. This is due to thermomechanical hardening of the material of the near-weld zone during welding. Post-annealing does not completely eliminate the effects of the welding cycle.
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