On the Amplitude Dependence of Energy Dissipation in a Welded Joint
Abstract Generated abstract
This paper investigates the amplitude dependence of energy dissipation, expressed through the logarithmic decrement of free torsional vibrations, in friction welded joints. The authors describe an experimental setup using electromagnetic excitation, strain gauge recording, and calibrated damped oscillation measurements on rod specimens welded under varied heating times, with attention to separating losses in the joint from other damping sources. The results indicate that the amplitude dependence of damping in welded joints has a form similar to that observed in solid metallic specimens, while the magnitude of energy dissipation is generally higher and strongly affected by welding quality. For the best welded specimens, the dissipation differed only slightly from that of a solid specimen.
Full Text
ON THE AMPLITUDE DEPENDENCE OF ENERGY SCATTERING IN A WELDED JOINT
V. I. MAKSÁK, K. P. ZAKHAROV, V. F. YAKOVENKO
(Presented by the scientific seminar of the Department of Strength of Materials)
By the present time, a large amount of data has been accumulated on the amplitude dependence of the internal friction of pure metals and alloys [1].
In the present work, studies have been carried out of internal friction in joints obtained by welding and friction, and the amplitude dependence of the logarithmic decrement of torsional vibrations has been established. Judging from the literature data, such a formulation of the question has been made for the first time.
When investigating energy scattering in a welded seam, it is necessary to separate it from the total energy. In the scheme considered below, the damping of vibrations in the installation is determined by aerodynamic damping, by energy scattering in the welded seam, in the base material of the specimen, and in the clamps. The energy losses in the base material due to aerodynamic damping, as well as the energy losses in the clamps at maximum tightening, are insignificant and remain approximately the same [2].
Fig. 1. Schematic diagram of the installation
The experiment is based on the method of free damped vibrations under loading of the specimens by an alternating torsional moment. The method of exciting the vibrations is electromagnetic. The schematic diagram of the installation is shown in Fig. 1. The lower head of specimen 1 is clamped with a force of 200 kN…
is placed in the slot of the press crosshead 2 by means of wedges 3, each having an inclination angle of \(8^\circ\). Clamping is carried out by moving the crosshead downward. A set of shims 4 and the presence of a shoulder on the support plate 5 make it possible to clamp specimens with different head sizes (from 10 to 30 mm). To the upper head of the specimen, by means of wedge 6, having an inclination angle of \(8^\circ\), the pendulum 9 is fastened through strip 7 with screws 8.
The pendulum is displaced from its equilibrium position by means of electromagnets, symmetrically and rigidly mounted on the columns of the press. The maximum moment thus produced is 100 N·m. After the electromagnets are switched off, the action of their alternating magnetic field on the armature ceases, and the specimen with the pendulum fastened to it begins to perform free damped torsional oscillations with a frequency of 22 Hz. Recording of the damped oscillations is carried out by means of strain gages (2FKRV-5-50KhV) 12, glued with cyacrine to the surface of specimen 1. The signal from sensor 12 is transmitted through amplifier (UT-4) 13 to loop oscillograph (N10) 14 and is recorded on photographic film in the form of a trace of the damped oscillations. At the same time, the signal of the time marker (P104) 16 is fed to the free loop of the oscillograph.
Recording of all oscillograms is carried out at constant signal amplification. For a more precise setting of the amplification according to the calibration pulse, a milliammeter 15 is provided in the circuit.
Fig. 2. Amplitude dependence of the logarithmic decrement of oscillations (1–14)—for rods joined by friction welding; 15—for a solid specimen. Steel 45
The specimens studied had the form of a rod 20 mm in diameter and 250 mm long. The surface finish of the cylindrical surface was \(\nabla 7\), and that of the contact surfaces of the specimen-head lugs was \(\nabla 8\). A high surface finish is necessary to reduce energy scattering in the clamps. For the same purpose, all contacting surfaces of wedges 3 and 6 must have a finish not lower than \(\nabla 8\). During the experiment, all contacting surfaces must be thoroughly cleaned. The specimens were made from end-mill blanks welded by friction on an MF327 model machine under different conditions (the heating time was varied from 3 s for specimen 1 to 12 s for specimen 14).
The annealing time was 15 hours at a temperature of 860°. The material of the working part of the blank was R6M3 steel; that of the shank was steel 45.
The experimental data obtained on the described setup made it possible to determine, from the sweep of damped oscillations, the logarithmic decrements for each specimen and to plot the graphs of their amplitude dependence (Fig. 2).
To calibrate the output signal of the strain gauges, a torsion-testing machine was used. As a result of analyzing the experimental data, the following may be stated:
- The character of the change in the amplitude dependence of the welded joint is such that
\[ \frac{d^{2}\delta}{dA^{2}} \]
changes from a positive value to a negative one, passing through zero, and corresponds to the character of the amplitude dependence obtained in [1] on solid specimens of various materials.
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Energy scattering in the welded joint is higher than in the solid material and depends to a considerable degree on the quality of welding.
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In the case of the best welding, the energy scattering in the welded joint differs little from the energy scattering in a solid specimen.
REFERENCES
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V. S. Postnikov. Internal Friction in Metals. Metallurgiya Publishing House, 1969.
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V. I. Maksak, K. P. Zakharov, B. F. Sovetchenko. Setup for investigating damped torsional oscillations of components joined by friction welding. In: Proceedings of the Scientific-Technical Conference “Engineering with Machine Building,” Dedicated to the 70th Anniversary of the Mechanical-Engineering Faculty of TPI, “Strength and Plasticity.” Part II, Tomsk, 1970.