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The work deals with the sliding contact of electrical machines. The work is focused on individual components of sliding contact and the evaluation qualitative criterions of certain components of sliding contact. In the final section is presented a comparative method that has been designed for large machines. In this work we used this method on a small machine.

The influence of the horizontal magnetic field has not been sufficiently studied in contrast to study activity on the influence of the vertical magnetic field by researchers. The reason was that the influence of horizontal magnetic field to change the wear mass loss of ferromagnetic materials is smaller compared to the vertical magnetic field. However, the influence of horizontal magnetic field on rolling contact changes the subsurface crack initiation point toward surface is postulated by a researcher. Therefore, it is significance finding out how the horizontal magnetic field influences the tribological characteristics. This thesis presents a study on the influence of the horizontal magnetic field on wear in sliding contacts contributes for ascertainment the effect and mechanism of horizontal magnetic field on tribological characteristics of sliding contacts, through the experimental approach.The static magnetic field with densities of 0 and 1.1 Tesla and different orientations was applied to different contact conditions, different surface modifications and two sliding frequencies, using a ball-on-plate contact configuration. In conclusion, the presence of magnetic field enhances the chemical adsorption between iron or oxide iron and oxygen, and causes the transition of adhesive wear to oxidative wear. Besides, the presence of magnetic field combined with low sliding frequency forms the bulging on the wear surface and weakens the prevailing wear mechanism due to the low frictional temperature. On the other hand, the presence of magnetic field combined with high sliding frequency induces the transition to the oxidative wear mechanism and reduces the wear. Also, distinctly different appearances of wear surface are created by different magnetic field orientations. In the lubricated sliding contact, the magnetic field causes the reduction of wear and induction of oxide. It is postulated that the presence of magnetic field enhances the oxygen adsorption on the wear track by iron wear particles and hence varies the tribological behaviour. The influence of magnetic field on carbon steel coating consists in changes of oxide iron layer and steel layer, alterations of mechanical properties of the coating, and decrease in the mass loss and the surface roughness on the dry sliding contact. All these could be suggested the influence of adhesive strength of the interface between the base material and coating.

Sheet metal forming processes are mechanical processes, designed to make products from metal sheet without material removal. These processes are applied extensively by the manufacturing industry to produce commodities such as heat exchangers or panels for automotive applications. They are suitable for production in large volumes. A typical problem in forming operations is accumulation of local sheet material adherents onto the tool surface, which may deteriorate the subsequent products. This tool failure mechanism is named galling. The aim of this work is to explain the mechanisms behind galling and establish factors how it can be reduced. The focus of this work is on the influence of tool material for minimum risk of galling. Experimental tool steels alloyed with nitrogen were designed and manufactured for systematic tribological evaluation. Reference tool materials were conventional cold forming tool steels and coated tool steels. The sheet material was austenitic stainless steel AISI 304, which is sensitive for galling. A variety of lubricants ranging from low to high viscous lubricants were used in the evaluation. The properties of the tool materials were characterized analytically and their tribological evaluation included industrial field tests and several laboratory-scale tests. The testing verified that nitrogen alloying has a very positive effect for improving galling resistance of tool steels. Tool lives comparable to the coated tool steels were achieved even with low viscous lubricants without poisonous additives. The hypothesis used for the explanation of the positive effect of nitrogen alloying is based on the critical local contact temperature at which the lubrication deteriorates. Therefore, the contact mechanism at the tool-sheet interface and the local energy formation were studied systematically. Theoretical considerations complemented with FEA analysis showed that a small size of hard particles with a high volume fraction gives low local contact loads, which leads to low frictional heating. Also, an even spacing between the hard particles and their frictional properties are of importance. Nitrogen alloyed tool steels have these properties in the form of small carbonitrides. The finding of this work can be applied to a wide range of applications that involve sliding metal contacts under severe tribological loading.

The work is devoted to the influence of dust particles on the operation of rotating machines with sliding contact. In the work are described and characterized dust particles from environment of selected machines. Their influence on sliding contact and influence on the insulation system of these machines is investigated.

This work presents a three dimensional elastic-plastic model for two hemispherical bodies sliding across one another under various preset vertical interferences. In particular, steel-on-steel and aluminum-on-copper contact situations are considered. A finite element analysis is used for the model and the parameters to investigate include stresses, deformations, contact areas, and energy loss in sliding. Both frictional and frictionless sliding are investigated. In addidition to structural loads, electromagnetic loads are considered and a framework for a electromagneticlly, structurally, and thermally coupled model is investigated.

Today, nonhomogeneous materials are used in many technological applications. Nonhomogeneity can be introduced intentionally in order to improve the thermomechanical performance of material systems. The concept of functionally graded materials (FGMs) is an example of such an application. Nonhomogeneity can also be an intrinsic property of some of the natural materials such as natural soil. The main interest in this study is on the contact mechanics of nonhomogeneous surfaces. There is an extensive volume of literature on the contact mechanics of nonhomogeneous materials. In most of these studies, the elastic gradation is assumed to exist in depth direction. But, it is known that elastic gradation may also exist laterally. This may either occur naturally as in the case of natural soil or may be induced as a result of the applied processing technique as in the case of FGMs. The main objective in this study is therefore to examine the effect of the lateral nonhomogeneities on the contact stress distribution at the surface of an elastically graded material. In the model developed to examine this problem, a laterally graded surface is assumed to be in sliding contact with a rigid stamp of arbitrary profile. The problem is formulated using the theory of elasticity and reduced to a singular integral equation. The integral equation is solved numerically using a collocation approach. By carrying out parametric studies, the effects of the nonhomogeneity constants, coefficient of friction and stamp location on the contact stress distribution and on the required contact forces are studied.

ABSTRACT CONTACT MECHANICS OF GRADED MATERIALS WITH TWODIMENSIONAL MATERIAL PROPERTY VARIATIONS G&ouml / kay, Kemal M.S., Department of Mechanical Engineering Supervisor: Asst. Prof. Dr. Serkan Dag September 2005, 62 pages Ceramic layers used as protective coatings in tribological applications are known to be prone to cracking and debonding due to their brittle nature. Recent experiments with functionally graded ceramics however show that these material systems are particularly useful in enhancing the resistance of a surface to tribological damage. This improved behavior is attributed to the influence of the material property gradation on the stress distribution that develops at the contacting surfaces. The main interest in the present study is in the contact mechanics of a functionally graded surface with a two &ndash / dimensional spatial variation in the modulus of elasticity. Poisson&rsquo / s ratio is assumed to be constant due to its insignificant effect on the contact stress distribution [30]. In the formulation of the problem it is assumed that the functionally graded surface is in frictional sliding contact with a rigid flat stamp. Using elasticity theory and semi-infinite plane approximation for the graded medium, the problem is reduced to a singular integral equation of the second kind. Integral equation is solved numerically by expanding the unknown contact stress distribution into a series of Jacobi polynomials and using suitable collocation points. The developed method is validated by providing comparisons to a closed form solution derived for homogeneous materials. Main numerical results consist of the effects of the material nonhomogeneity parameters, coefficient of friction and stamp size and location on the contact stress distribution.

Subject master´s thesis is design of a measuring device for the study of sliding contact. It including description sliding contact, its importance and application possibilities. Specification of examination possibilities of sliding contact, indicate the possibilities of evaluating the measured results. Design a stationary measuring device for long-term tests of the sliding contact and verify its the basic system concept. Master´s thesis including too elektronic make graphes with courses quantity on real machine.

This thesis deals with the sliding contact of electrical machines and its diagnostic methods. Namely, the dust-particles method for assessing the length decrease of brushes is deeply described. Then, usage of the method in industry is described. The comparison of accuracy between manual version and new automated version of the method using computer analysis is presented. The final section is devoted to the practical verification of the new automated version which was developed especially for large machines. Measurements were performed on a small machine.