OBRABOTKAMETALLOV technology Vol. 26 No. 3 2024 Results and discussion Effect of shear vibrations on the assembly process and the threaded joints properties Processing the experimental results found the dependence of the change in the relative torque of loosening on the amplitude of vibrations Tl (ξm) (Fig. 3), where ε is the standard error of evaluation. Fig. 3. Dependence of the relative unscrewing torque on the amplitude of shear ultrasonic vibrations for size M8 Shear vibrations of any amplitude lead to an increase in the Tl. Active growth occurs before the amplitude of ξm increases to 5 µm – the relative torque of loosening increases by 1.5 times. In this case, Topen is about 30 Nm, which exceeds the value without vibrations by 48 %. With a further increase in the amplitude above 5 µm, no significant changes occur, the increase in Tl is in the range of 1.4–1.5 times. The increase in Tl under ultrasonic vibrations can be explained by a change in the balance of forces during assembly. When shear vibrations are applied with a horizontal arrangement of the assembled joint, the diagram of the forces acting on the joints looks as follows (Fig. 4): The main forces acting on the joint during assembly are such forces as the wrench tightening force Fclose; the friction force Ffr directed in the projection in the opposite Fclose direction; the axial force F0 directed from the bolt head; gravity mg; the force excited by the movement of the joint with an ultrasonic frequency Fus = Fcosωt, where ωt is the vibration phase (ω = 2πf, where f is the vibration frequency); inertia forces Fin. Inertia forces are understood as centrifugal force Fcf and Coriolis force Fk [36]. In this case: Fin = Fcf + Fk. According to the diagram in Fig. 4, the equation of motion has the following form (2): sin cos cos sin sin cos 0 , close mg F F F F m F fr i a n - ϕ - - ϕ - ϕ ϕ = ϕ + ω (2) where φ is the angle of thread elevation. Fig. 4. Diagram of forces when shear vibrations are applied to a horizontal joint
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