OBRABOTKAMETALLOV technology Vol. 26 No. 3 2024 a decrease of 40 %. At the same time, the step parameters increased by 35 % and 54 % for conventional assembly and assembly with ultrasound, respectively. These changes indicate an increase in the friction force on the support surface, as a result of which the loosening force becomes greater. Also, the profile crushing shows an increase in the axial force, which prevents the joint from loosening. Studies have also been conducted on the effect of shear ultrasonic vibrations on the deformation of thread turns with an increase in torque. To do this, the joints were assembled with a gradual increase in Tclose from 24.5 to 27; 29.5; 32; 42 Nm. After assembly, under the influence of vibrations, the joint was disassembled without ultrasonic treatment, after which the bolt thread profile was evaluated using a contour measuring station. The vibration amplitude was 6 µm. The results obtained were compared with profiles obtained by tightening without ultrasound. When tightening without vibration up to 24.5 Nm, the thread profile is not deformed. The first signs of exceeding the deformation limit are found at 27 Nm, while at 29.5 nm, the deformation is more pronounced. At 32 Nm, the final thread failure occurs on 2–4 turns with severe deformation of the 5th turn (Fig. 5). When ultrasonic treating at 29.5 and 32 Nm, there are no signs of deformation, and the deformation limit is shifted to 42 Nm. This confirms an increase in the permissible Tclose in the absence of damage to the assembled joint, and, as a result, an increase in the quality of the joint. A comparison of the change in the length of the thread turn by turns at the maximum Tclose is shown in Fig. 6. Fig. 6. Graph of the dependence of the length change of the thread turns on the number of the thread turn This dependence shows that using ultrasound leads to increased uniformity of load distribution along the turns of the thread, which practically does not change from the 1st to the 5th turn, while without ultrasound, the main load is experienced by the first three turns. This makes it possible to increase the torque while significantly reducing the probability of deformation of the thread turns, which leads to an increased strength of the joint. Effect of ultrasound on the properties of epoxy adhesive The dependence of the viscosity change on the ultrasonic treatment mode ηi/η0(ξm, t) is shown in Fig. 7. The initial viscosity before treatment was h0 = 4,400 MPa⋅s. Ultrasonic treatment at any amplitude leads to a change in the viscosity of the epoxy adhesive. At the same time, for each of the considered modes, the change occurs in three stages: the first is a sharp decrease in viscosity by 50–80 %; the second is the treatment period without significant changes; the third is a sharp increase in viscosity, up to levels above the initial one.
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