George Tumanishvili

By George Tumanishvili, Tengiz Nadiradze and Giorgi Tumanishvili

At present, Nadal’s formula is used for prediction of derailment that contains a limited number of parameters. Besides, insufficient study of laws of variation of the noted parameters and ignorance of the influence of other parameters on the derailment complicate solution of the problem. The sliding distance and the relative sliding velocity are the most sensitive factors contributing to the destruction of the third body. Moreover, increased friction coefficient between the steering surfaces of the wheel and rail promotes climbing of a wheel on the rail and derailment. Dependences of the main parameters, influencing the destruction of the third body, the sliding distance and the relative sliding velocity on the rail track curvature, and difference of diameters of wheels of the wheelset and the non-roundness of one of the wheels of the wheelset are shown in the work. The methods for estimation of the third body destruction degree and consideration in Nadal’s formula of the additional criterion of impossibility of the wheel rolling on the contact point of the wheel and rail steering surfaces, containing a value of this contact point advancing, which in turn depends on the angle of attack, are proposed.

Part of the book: Transportation Systems Analysis and Assessment

By George Tumanishvili, Tengiz Nadiradze and Giorgi Tumanishvili

The methods of estimation and prediction of tribological properties of the contact zone of interacting elements of machines are characterized by the low informativeness and accuracy that complicates provision of the proper tribological properties and hinders reliable and effective operation of machines. For obtaining more wide information about factors influencing tribological properties of the interacting surfaces, the experimental researches on the high speed (up to 70-m/s) and serial twin-disk machines were carried out. Our researches have shown that with different properties and degrees of destruction of the third body, the coefficient of friction can change up to 10 times or more, the wear rate up to 102-104 times, etc. This was the basis for a new concept of the mechanism of variation of tribological properties of interacting surfaces. The researches have shown a dependence of tribological properties of the contact zone on the properties and destruction degree of the third body that was assumed as a basis of new concept of the mechanism of variation of tribological properties of these surfaces. The monitoring of the third body destruction onset and development was carried out in the laboratory conditions and a criterion of the third body destruction was developed. The reasons of the negative, neutral and positive friction and mild, severe and catastrophic wear are shown.

Part of the book: Tribology in Materials and Manufacturing

By George Tumanishvili, Tengiz Nadiradze, Rustam Rakhimov and Giorgi Tumanishvili

An increase in the friction path and sliding velocity contributes to an increase in thermal loading and wear of heavily loaded rubbing surfaces of wheels and rails. One of the reasons contributing to the development of these phenomena is the change in the shape of the rubbing profiles of wheels and rails due to wear. Conditions of power and thermal loading and increased wear rate of profiles of the wheels and rails are considered, and friction paths and sliding velocities are calculated at movement of new and worn wheels of the wheelset in the straight and curved sections of a rail track. It was revealed that wear of the profiles significantly increases friction path, sliding (friction) velocity, and frequency of lateral oscillations (zigzag movement) of the wheelset in the straight sections of the path along the rolling surface and in curved sections—the friction path of the inner wheel. Therefore, change of the wheel profile due to wear negatively affects the frequency of the wheelset lateral oscillations, friction path, sliding velocity, and wear rate that should be taken into account when determining wear norms of the wheels and rails.

Part of the book: Railway Transport and Engineering - A Comprehensive Guide [Working title]