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4Hanziuk Andrii Leonidovich graduate student of department of wearproofness of machines Khmelnytsk national university Oleksandrenko Victor Petrovich doctor of engineering sciences, professor dean offaculty of engineering mechanics Khmelnytsk national university
Ганзюк Андрш Леотдович
астрант кафедри 3HococmmKocmi машин Хмельницького нацiонального утверситету Олександренко ВЫтор Петрович
доктор mexHi4Hux наук, професор, декан факультету iнженерноi меxанiки Хмельницького нацiонального утверситету
PROTECTION OF SURFACE OF NOMINAL-REAL ESTATE DETAILS IN THE CONDITIONS OF SMALL-AMPLIFIED FRETING BY Bi-Sn-Pb-Cd BASES
ЗАХИСТ ПОВЕРХОНЬ НОМ1НАЛЬНО-НЕРУХОМОГО КОНТАТУ ДЕТАЛЕЙ В УМОВАХ МАЛОАМПЛ1ТУДНОГО ФРЕТИНГУ СПЛАВАМИ НА ОСНОВ1 Bi-Sn-Pb-Cd
Summary: Analysis of type of damages of functional elements of motor-car technique has showed that the damage of metal is related to the accumulation and cooperation of defects of structure, by chemical cooperation of metal and environments by an increase little-amplified frettage. Character of change of force of friction is investigated and set in nominally-immobile connections on the stage of nominal adhesion and to passing to skidding. Recommendations for increase the capacity of nominally-immobile connections are given by the method of coating on the basis of fusible to the alloy of Bi-Sn Pb-Cd.
Key words: fretting process, force offriction, capacity of connections.
Аннотация: Анализ вида повреждений функциональных элементов автомобильной техники, показал, что повреждение металла связано с накоплением и взаимодействием дефектов структуры, химическим взаимодействием металла и среды усиленным малоамплитудным фреттингом. Исследовано и установлено характер изменения силы трения в номинально-неподвижных соединений на стадии номинального прилипания и переходу к скольжению. Даны рекомендации повышения работоспособности номинально -неподвижных соединений методом нанесения покрытия на основе легкоплавкого сплаву Bi-Sn-Pb-Cd.
Ключевые слова: фреттинг-процес, сила трения, работоспособность соединений
Formulation of the problem. The solution of the scientific and technical problem, namely the fight against friction and the increase of wear resistance of surfaces of parts, which are in nominally-fixed contact, does not lose its relevance. According to operational estimates [1], the reduction of losses from the wearing of critical parts will allow one-third to cut costs for repair and operation of various types of machinery. Friction is the initiator of dynamic, deformation, thermal, adhesion and other processes that affect the working life of friction units, their energy performance and efficiency [1, 2]. It is known that the work life of tribocompounds is limited to premature wear or destruction of contacting parts, including as a result of the emergence and development of a special type of surface damage - fretting corrosion. The phenomenon of fretting, as one of the contact types of interaction, is due not so much to the problem of wear of friction units, but with the danger of a sudden failure of nominally-immovable connections, and therefore the study of the influence of external factors on the process of fretting-wear is an urgent task.
Analysis of recent research and publications. It
is known [2] that one of the main reasons for the loss of integrity of the connection is the fringing process (AF),
the causes of which are the characteristic relative motion and microplacing of contact surfaces. The flow of AF at low amplitudes is characterized by complex dynamics and instability of relative motion [2]. Therefore, the nature of phenomena with low amplitude Freight is still far from a holistic conclusion. Thus, the notion of the upper boundary of the low-amplitude fretting remains rather uncertain. This is due to the fact that with small displacements of surfaces and even a sufficiently large number of oscillations, it is difficult to determine the degree of damage to the contact. At present, it is thought that the upper limit of the low-amplitude fretting is 30 ... 35 microns [3]. Also, it remains unclear what the relationship should be between slipping and clutching in the relative displacement of surfaces in order to assume fretting at low amplitude. The use of automatic equipment in terms of the reliability of mounting points and AF is distinguished by the main factors: the unsteadiness of dynamic loads and the influence of the external environment [2]. It is precisely the non-stationary load that results in the sudden destruction of the knots of the real conjugation, and the concealment of the long-term action of the fretting does not allow for the prediction of an emergency situation.
¡' II" "
Fig. 1. View of the section of the right axle of the front wheels of the car's semitrailer
Selection of previously unsettled parts of the general problem. The analysis of the color of the surface of the parts (Fig. 1, Fig. 2) and the type of destruction of the functional elements, under the action of cyclic dynamic operating loads, shows that the damage to the metal is associated with the accumulation and interaction of structural defects, the chemical interaction of the metal and the environment by amplified low amplitude fretting.
The purpose of the article. The purpose of the study is to determine the nature of the friction at the stage of nominal adhesion and in the transition to slip and to ensure the performance of nominally-immobile friction compounds due to the increase of their fretting resistance using a coating method based on the low-melting alloy Bi-Sn-Pb-Cd.
Presentation of the main material. AF is determined by a complex set of mechanical and chemical processes that occur in the contact area of two surfaces. We can state that this type of interaction is manifested
Fig.2. Appearance of damage to the car's hinge threaded part
in most cases when exploiting nominally-fixed compounds, when there are no visible relative displacements [4]. The difficulty lies in the fact that to a certain magnitude of stress and deformation of the surface, the amplitude-frequency characteristic of the vibrations of two bodies is practically the same, which excludes the relative displacement of surfaces.
Obtained results (Fig. 3): the evolution of the contact zone of the sample at the installation for the study of parameters of fictional contact [5]. The study of the surface of the samples showed that there are lesions characteristic of fritting. The complex combination of surface adhesion, elasticity of the contact layer and dynamic phenomena in the system "contact - sub surface layer - body as a whole" does not give the precise value of the amplitude of slip according to the usual measurement method. For investigation of friction, three basic principles are proposed: the law of friction with low velocities, the contact dynamics in general and the determination of the latent features of the surface contact evolution in cyclic and tangential oscillations.
Fig. 3. Evolution of the contact zone of the sample with fluctuations in the scheme of a metal ball (12.7 mm) and
a flat surface
The mechanical system with oscillatory friction is non-stationary or heterogeneous. Vibration diagnostics of the working state of nominally-fixed compounds is based on the analysis of vibration for fretting, and the main indicator of the working condition of the connection is the intensity and nature of these processes. The amplitude-frequency characteristic of the vibration signals from the contact pair was determined by the rapid Fourier transform [4.5]. The search for peculiarities in
vibration signals, energy characteristics of micro cracking, long-term trends and trends were determined by wavelet analysis of time series of fretting processes. The key point is that the basic Fourier transform highlights the spectrum of a function, signal, image, etc., but this frequency division is global rather than localized; while the wavelet transform provides the localized frequency decomposition. It provides information not only about what frequency components are present in the signal, but also about when and where they occur.
Consider the results of the wavelet analysis (WA) on the example of the evolution of the frictional force presented in Fig. 4. Application of WA shows that in the mode of full previous displacement there are fluctuations of fictional force (Fig. 4). This is due to the uncertain strength of static friction. In a moment, that
precedes the initial slip, frictional forces become unstable due to the forces of elasticity and inertia. WA for frequencies less than the frequency of forced oscillations shows the evolution of quasi static friction within the limits of nominal adhesion. Most of the vibroactiv-ity is observed at the initial moment of oscillation and in the transition from adherence to slip (Fig. 5).
0 00e+00 4.00e-01 8.00e-01 120b*00 1.60e+00 . ■ 210e+00 2.80e+00 3 20e*00 3.60e+00 4.00e'00
time.s
Fig. 4. Wavelet transformation of a time series for friction with its gradual reduction and transition of a contact
from sticking to slip. Frequency of excitation of 50 Hz
Fig. 5. The intensity of the amplitude-frequency characteristic on the large scale of wavelet transformation
The analysis in the field of small frequencies vibrational activity of the frictional force at the stage of shows large-scale changes in the process with the am- nominal adhesion and during the transition to slip (Fig. plitude-frequency characteristic of the signal for a fixed 6). time of evolution. Scanning wavelet diagrams for low frequencies determines the quantitative picture of the
Fig. 6. Evolution of static friction over time
The method of increasing the fretting stability of nominally-fixed compounds by applying a paste on the basis of a low-melting Bi-Sn-Pb-Cd alloy with subsequent melting of a laser beam [6] is proposed, which provides: to create the effect of screening the surface of a solid from the action of the environment, above all diffusion of gases radicals: oxygen, hydrogen and carbon dioxide; reduction of adhesion of contacting surfaces of bodies; creation of conditions for the appearance of liquid friction at separate points; reduction of equivalent stresses in the surface layer; formation of a third body from oxidation products. The impurities in the form of Bi-Sn-Pb-Cd change the diffusion conditions and lead to a change in the rate of the oxidation reaction in the case when the ions of impurities are in-
cluded in the product of the interaction. The introduction of ions of impurities of inert elements in the vacancy of a crystalline lattice leads to a decrease in the concentration of the ion of the matrix in the interstitials, and as a result and to a decrease in the rate of oxidation of the matrix.
Photographic studies of samples were carried out on a metallographic microscope MIM-10. From the analysis of the surface of the samples, it was found that the interaction between the fusible alloy Bi-Sn-Pb-Cd and the surface of the matrix follows the adhesion mechanism. In the photographs it is seen that the grappling of the alloy (dark background) with the surface of the matrix (light background) and the formation of metal joints (Fig. 7).
a b
Fig. 7. Photos of the surfaces of samples from steel 45 in the presence of a fusible alloy Bi-Sn-Pb-Cd on the surface of a solid after the wear process: a - an increase in the surface area (100: 1); b - an increase in the
surface area (250: 1)
In the course of experimental studies, the coefficient of friction of the specimen, which was in nominally and immovable contact with the matrix, was determined, as well as the intensity of wear of the matrix from steel 45 in air and in the presence of a fusible alloy
in the fretting zone at a nominal pressure of 12 MPa, amplitudes of vibrations of 50 ^m, counterfilm - tempered steel 45, exam base - N = 1x106 cycles. Significant coefficient of friction (curve 1, Fig. 8) indicates a high degree of adhesion, and some of its stabilization at
a certain level says that the third body is formed by adhesion wear [7]. The presence of a low-melting alloy significantly reduces the mechanical action during friction-wear, as evidenced by curve 2 (Fig. 8). This pro-
f
vides a small but constant value of the friction coefficient f which is set after the spin (Fig. 8). Fig. 9 shows the intensity of wear of steel 45 under different conditions.
1x10 ,mg//j.m x dele
0,25
0,2
015
0,1
005
1
2
0
/ /
0
0,2
OA
0.6
0,8 N x106 adi 0,2 0.3 OA 0.5 0,6 0,7 0,8 N x106, odes
Fig. 8. Change in the coefficient of friction during fretting: 1 - steel 45 in the air;
2 - in the presence of a fusible alloy in the friction zone
As a result of the conducted researches it was established that in the presence of a fusible alloy in the fretting zone, the wear rate decreases two to three times in comparison with friction without an alloy due to the presence of a fusible alloy in the fretting zone and is achieved by a significant decrease in the diffusion of active radical gases in the surface solid body.
Thus, in the presence of a fusible alloy in the fretting zone, a significant resistance to adhesion of the juvenile surfaces and oxidation wear will be provided.
Conclusions
Analysis of the results of wavelet transformation made it possible to identify those barely noticeable changes in the nature of the relative motion of surfaces in the diagnosis of nominally-fixed compounds. It is important that the time series analysis can be carried out at different time scales in order to find out the tendencies in the long-term evolution at low frequencies and operate on a smaller scale at high frequencies.
The wavelet analysis complex has shown the existence of a frictional contact, which is set at the boundary of transition from static friction to kinematic and is classified as dynamic clutch-slip mode (see Fig. 4, Fig. 5). In the areas of clutch, with the corresponding number of load cycles, there is a bundle of individual sections of the surface (see Fig. 3), and the transformation of the frictional force (Fig. 6) in the slip zone leads to a change in the quantitative characteristics of the dynamic motion of the system, in other words, to loosening from' unification.
The results of experimental studies have shown that when the contact surfaces of the Bi-Sn-Pb-Cd separated by a low-melting alloy are reduced by a factor of two, the friction coefficient decreases twice and the
Fig.9. Intensity of wear of steel 45: 1 - in air; 2 - in the presence of a fusible alloy in the friction zone
wear rate is two to three times as compared to non-alloy friction.
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