5. Conclusion remarks and future works

Prediction and avoiding of derailment are the most important problems of which many scientific works are devoted for their solution but the desirable results are not obtained yet. The survey of the literature and our experience show that the derailment is especially influenced by the friction coefficient that is not predictable, and in contrast to other parameters, it varies in a wide range.

It is shown that for prediction of the friction coefficient and providing its stability, it is necessary to provide the contact zone with the continuous and restorable third body of due properties.

The main results of the paper can be formed as follows:


less value (more conservative) of the allowable ratio of lateral and vertical forces than Nadal's formula.

For solution of the problem of derailment, an experimental–theoretical approach is needed because of the lack of comprehensive theoretical model of the wheel climbing on the rail.

Due to the existence of materials with quite different designations and properties in the contact zone, many new unanswered problems rise. They are related with the further increase of the derailment criterion informativity and precision, providing the contact zone with the third body having due properties, conditions of formation, and destruction of the third body. They also concern to the tribological properties of the interacting metal and nonmetal surfaces, direct interaction of their juvenile surfaces and generation of the strong adhesion bonds, cold welding, destruction and wear of the surfaces, variation of the value, and instability of the friction coefficient.

On the base of experimental researches, we have ascertained dependence of the friction coefficient on the degree of destruction of the third body for the conditions of various relative sliding velocities, speeds, materials of interacting surfaces, roughness of the surfaces, friction modifiers, and loads at which the range of variation of the acting parameters is quite wide and therefore continuation of researches is needed.
