Influence of thermophysical processes occurring in the zone of moving contact on the mechanical properties of the surface layer of materials

Abstract

Purpose. Determination of mechanical properties of the surface layer of materials and physical processes occurring in the zone of frictional interaction of the wheel-rail pair. The methods. On the basis of theoretical studies of the parameters of the movement of a vehicle along a rail track, a mathematical model of the interaction of a wheel and a rail on an elementary contact area in the presence of normal and tractive effort is formulated.The nature of the change in the phase composition and the heterogeneity of the structural state, which can lead to a decrease in the mechanical properties of a wheel-rail pair and a decrease in the overall operational reliability of these products, have been investigated. The structural state of the wheel rim after various modes of heat treatment has been investigated. A mode of heat treatment is proposed, which consists in differential cooling of the wheel rim on a vertical hardening machine with a change in the intensity of heat removal, which makes it possible to obtain a homogeneous structure over the section of the wheel rim, as well as to increase its mechanical characteristics. Findings. When bodies interact with a moving contact point, it is necessary to take into account the physical and mechanical properties of the surface layers, which differ from the properties of a material located at a considerable distance from its surface. This difference arises as a result of chemical and structural transformations, mechanical and thermal effects, wear and contact fatigue of the surface materials of the wheel-rail friction pair. The modes of heat treatment are proposed, which provide structural homogeneity and improve the mechanical properties of the wheel rim. Practical implications. A dependence is obtained that describes the change in the average temperature in the contact patch of a wheel-rail pair on the speed of a rail vehicle. The current value of the elastic modulus of the friction pair material is determined as a function of the contact time. The modes of heat treatment of steels are described, which make it possible to obtain chemical uniformity over the section.