THE RESEARCH OF THE RAILWAY RAIL FOR ANALYSIS OF SURFACE INITIATED ROLLING CONTACT FATIGUE CRACKS
Keywords:rails and wheels of railway transport, wear and stability of rails of railway track, contact damage, defects of rails, contact fatigue cracks, number of load cycles, magnetic powder method of non-destructive testing.
Problems. Under the influence of dynamic loading from trains and natural conditions, the railway track deteriorates, characterized by the appearance of defects and residual deformations of the railway track, which lead to accelerated wear and malfunction of other elements of the rail. The appearance of the specified defects, failures and destructions of the elements of the rail grating is associated with the action of additional local stresses arising in the rails of the railway track. On a low-quality track grating with deviations of the parameters of the rail track, when the train is moving, there is an unaccounted interaction of the track and rolling stock with local overload of the interaction elements along the path. As a rule, the unaccounted interaction of track and rolling stock is accompanied by the impact of the wheel and the rail with overloading the contact area. When the impact of the wheel and rail strikes, stresses exceeding the endurance limit occur in the rail head. In this case, the rails are born in the head and begin to develop defects of contact-fatigue origin in the form of horizontal vertical and transverse cracks.
The aim of the study. Conducting practical studies of the origin and development of contact-fatigue cracks by wear of the rails in the laboratory.
Methods of implementation. An experimental unit was designed and manufactured to investigate the rails for contact damage. The unit 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 bulk of the experimental setup contains a wheel-rail friction unit. The force of clamping the rail to the wheel. Provides a hydraulic system. For testing, a test program was developed, which provides for two-hour tests, after which tests for the presence of defects (micro cracks) on the rail are conducted. Research on the presence of defects is carried out by the method of magnetic powder non-destructive testing.
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 papers, 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 cause of the origin and development of contact fatigue defects in the rail head is insufficient contact fatigue strength of the rail steel. For carrying out practical researches in laboratory conditions the methodology was developed, the experimental unit was constructed and made. Experimental studies have shown that the occurrence of defects on the surface of the rail is observed after 200-250 thousand load cycles. With the 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.
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