On the assessment of the mechanical characteristics of rail steels under operating conditions

Abstract

620.178.15/625.143 and N. Ya. OpravkhataThe analysis of the mechanical state of the materials of a new rail and a rail after long-term operation are performed on the basis of the obtained data on the distributions of hardness over the cross sections of rails and the spread of the characteristics of hardness.Keywords: residual and contact stresses, hardness, spread of values of the characteristics of hardness. Introduction.In the course of operation, the materials of heavy-duty structures undergo various types of changes. Thus, in new products, we observe the processes of adjustment of the components with intense wear of the working surfaces, as well as the processes of adaption of the upper layers of the materials to the modes of operation, temperature conditions, etc. The indicated adaptation leads to irreversible structural changes in the materials, which, as a rule, increase their serviceability [1]. The subsequent long-term operation promotes the initiation and development of defects in the materials of the workpieces. It is clear that all these processes are typical, in particular, of the materials of wheel-rail systems.The structural inhomogeneity of structural materials prior to operation manifests itself in the spread of values of its mechanical characteristics in local volumes. A noticeable structural inhomogeneity of the material of the rail in the intact state caused by the technological processes of its manufacturing (rolling, thermomechanical treatment of the entire rail or its head, etc.) increases in the course of operation. The inhomogeneity of the mechanical properties of structural materials over the cross section of any product is estimated according to the distribution of the values of hardness. In this case, the analysis of inhomogeneity of the properties of materials is performed both on the basis of direct values of hardness [2, 3] and by using statistical methods [4][5][6]. The approaches extensively used in practice enable one to monitor (without significant costs) both the state of load-carrying elements and the accumulation of defects in the local zones of structures without their destruction [4].If a wheel rests on a rail, then a three-dimensional stressed state is formed in the central part of its head. In the case of hunting of a train, the contact zone shifts toward the working fillet. In this case, one may observe the realization of two-point contact as a result of the interaction of the wheel flange with the rail. This leads to the formation of a stressed state close to pure shear [7]. The action of numerous factors of different nature affecting the stress-strain state of the railway bed results in the necessity of a large number of replacements of defective and highly defective rails in the railway tracks and frequent failures of rails, which is especially dangerous for the mainline railways with fast motion of passenger and heavy freight trains.The levels of operating loads and the fields of residual stresses play a significant role in the operation of rails. In passing all ...

Influence cooling to 213 K for strength rail steel

“…Проведенні експериментальні дослідження [19][20][21] механічних властивостей рейкових сталей в умовах дії електричного струму, знижених температур та попереднього напрацювання показали, що підчас безперервної довготривалої експлуатації колії фізико-механічні властивості рейкової сталі зазнають значних змін.…”

“…1) [19,20] Як видно з наведених у табл. 2 даних, значення допустимих розрахункових напружень матеріалу рейки після експлуатації при температурі 293 К значно більше (на 26 %) мінімального значення регламентованого нормативним документом [18].…”