Background. Continuous mechanical loads on the rails during its contact with the wheel lead to an accumulation of residual stresses in the surface layers of the rails, resulting in fast-growing fatigue cracks. In addition, the interaction of the wheel and the rail leads to micro-and macro-slip during their contact, abrasive wear, as well as plastic deformation of the rail. Rail grinding is the repair method by which defective material layers removes from the rail surface, provides the necessary accuracy of size and shape as well as surface quality.Objective. The aim of the work is to determine the effect of grinding on the tribological properties of the rail surface and establish the optimal parameters of the grinding process to ensure the best wear resistance of the rail surface. Methods. The research on wear and contact damage of samples of surfaces cut from grinding rails conducted on a friction machine M-22M. The studies were carried out by dry friction of a sample (cut from a rail) with a counter-sample from the material used in the manufacture of railway wheels, for 1 hour, the friction path was 3.60 km. Samples were weighed on a VLR-200 balance before and after the study was performed on the friction machine. As a result, the mass wear value was determined for each sample. Results. Based on the results of tribological studies, we obtained graphical dependencies of the wear intensity on the hardness of surfaces of samples and histograms which showing the effect of grinding process parameters on the amount of the wear intensity of samples. In the work was investigated influence the next main parameters of the grinding process on wear resistance there are the temperature of the rail, depth of cut, grinding wheel speed. The results of the work can find practical application in railway transport when repairing rails by grinding. Conclusions. Based on the analysis of experimental data, the empirical relationship revealed between the depth of cut, the surface hardness of the sample and the intensity of its wear. The nature of the influence of grinding process parameters (rail temperature, depth of cut, grinding wheel speed) on the wear resistance of the rail surface is established. The most optimal values of the process parameters that provide greater wear resistance of the rail surface are depth of cut -0.007 mm, grinding wheel speed -30 m/s, rail temperature -20°C (it is better to conduct the processing of rails in the warm season). The results of the work can find practical application in railway transport when repairing rails by grinding.

Background. The current operating conditions of railway transport characterized by an increase in the power of locomotives, train speeds and carrying capacity, which leads to increased force influences on the railway track. Extreme operating conditions lead to increased wear and damage to rails on the reliability of which depends not only on traffic safety, but also the economic performance of the railway. Defective layers of the material removes from the surface of the rail by the rail grinding process. Thus, provides the required sizes and shape accuracy, as well as surface quality of rails during their operation. Objective. The aim of this work is to develop a tribological model of contact wear of rails during their operation depending on parameters of the grinding process (temperature t, grinding depth of cut ae, grinding wheel speed V). Methods. The research on wear and contact damage of samples of surfaces cut from grinding rails conducted on a friction machine M-22M. The studies were carried out by dry friction of a sample (cut from a rail) with a counter-sample from the material used in the manufacture of railway wheels, for 1 hour, the friction path was 3.60 km. Samples were weighed on a VLR-200 balance before and after the study was performed on the friction machine. As a result, the mass wear value was determined for each sample. A numerical model created in the Ansys program for numerical simulation by the finite element method of the rail-wheel contact to determine the contact pressure distribution and the wear intensity of the rail. Results. Based on the results of tribological studies in the paper established the empirical dependence of the wear intensity of the rail sample on the grinding process parameters. The contact conditions of the rail sample with the counter-sample during the tribological experiment and in real contact of the rail-wheel are different. Therefore, we performed the alignment of that empirical dependence to the actual conditions of contact of the wheel with the rail. The rail-wheel contact simulation performed in ANSYS Workbench. The dependence that given in the paper used in the program. It used to calculate the wear intensity of the rail according to the distribution of contact pressure in the contact zone of the wheel and rail. The results of the work can find practical application in railway transport to predict the effect of grinding proces parameters on the wear intensity of the rail. Conclusions. The dependence obtained for the approximate value of the rail wear intensity depending on the grinding process parameters (temperature t, machining allowance ae, linear speed of the grinding wheel V) based on the experimental data obtained from tribological experiments on the M-22M friction machine with grinded rail samples. The mathematical model has developed for calculating the contact pressure and the value of the rail wear intensity depending on the number of load cycles in the ANSYS program.

Problems. Under the influence of dynamic loading from trains and natural conditions, the railway track deteriorates, which is characterized by defects (warps, subsidence, shocks and other residual deformations of the railway track), which lead to intense wear and collapse of all elements of the rail track panel. Listed defects precipitation, failures and destructions of elements of the rail track panel is related with additional local stresses that occur in the railway track rails. On a low-quality rail track panel with high parameters deviations, during the train movement, there is an unaccounted interaction of the track and rolling stock with local overload of the interaction elements along the path. Usually, the unaccounted interaction of track and rolling stock is accompanied by the wheel and rail impact with followed contact area overloading. During the wheel and rail impact, stresses that exceed the ultimate strength are occurring in the rail head. In this case, defects of contact-fatigue origin in the form of horizontal, vertical and transverse cracks are born and start to develop. The aim of the study. Conducting practical studies of the contact-fatigue cracks origin and development by studying rails wear in the laboratory. Methods of implementation. For research of rails for contact damage experimental setup has been designed and manufactured. The setup is mounted on a mechanical single-cylinder press of the K 2322 model with a nominal force of 16 tons at a nominal stroke frequency of 120 per minute. The main part of the experimental setup contains the friction unit "rail-wheel". The hydraulic system provides needed clamping force of the rail to the wheel. A test program, which provides for two-hour tests, followed by defects (micro cracks) detecting on the rail body has been developed. Research on the defects presence is carried out by fluorescent magnetic particle inspection method. Research results. Studies have shown that contact-fatigue cracks in the rail head occurred after approximately 200 thousand load cycles. This generally coincides with the results presented in other works, which show the occurrence of similar damage after 190-290 thousand cycles, depending on the properties of rail steel (hardness, surface roughness, etc.). Conclusions. The main reason for the origin and development of contact-fatigue defects in the rail head is the insufficient contactfatigue strength of rail steel. For carrying out practical research in the laboratory, the experimental setup has been designed and manufactured. The test program has been developed. Experimental studies have shown that the occurrence of defects on the surface of the rail observed after 200-210 thousand load cycles. With further increase in the number of load cycles, there is a rapid development of existing contact-fatigue cracks and the formation of new cracks in the contact zone.