2. Dependence of the friction coefficient on the degree of destruction of the third body

The phenomenon of seizure is typical for interacting surfaces. This may occur when the third body is destructed and the surfaces are juvenile (free from dirty, oxide films and adsorbed layers) and are approached sufficiently. Seizure of the interacting surfaces leads to the most dangerous and dominating kind of deterioration—scuffing.

For prevention of this phenomenon, they try to improve the tribological characteristics of the contact zone (improve properties of contacting surfaces and their ambient by applying the friction modifiers), stabilize the boundary layers, minimize a sliding distance and relative sliding velocity, etc. As it is noted in [23], the variation of the friction coefficient is mainly caused by changing a composition of the interfacial layer (the "third body") between interacting surfaces. Our experimental researches have shown that for the given friction modifier, the variation of the friction coefficient mainly depends on the degree of destruction of the third body. An increase of the relative sliding velocity leads to an increase of the friction power and the contact temperature and decrease of the lubricant viscosity, film thickness, and friction force (friction coefficient). It corresponds to the "negative friction" in Figure 2, where a friction/creep relationship is shown [24].

Worsening of the working conditions is caused by the partial, unit seizures and nonprogressive damage of the third body in the separate unit places (Figure 3) that corresponds to the separate small impulses of the friction moment. In Figure 3 are shown the stages of damage of the interacting surfaces due to seizures and scuffing of the surfaces.

Figure 2. Friction/creep relationship.

Figure 3.

The stages of damage of the interacting surfaces due to seizures and scuffing of the surfaces: (a) unit seizures, (b) multiple seizures, (c) seizures in the form of the narrow strip, and (d) seizures on the whole area of the roller.

The further extension of destruction of the third body in the multiple places leads to the multiple damage of the third body, multiple adhesive junctions of micro-asperities, disruption of these junctions, and comparatively increased impulses of the friction moment and to "neutral friction."

A progression of the third body destruction leads to spacious, discontinuous third body, adhesive junctions of micro-asperities, disruption of these junctions, and increase of the friction forces ("positive friction"). As it is seen from Figure 2, negative, neutral, and positive behaviors of the friction forces are stipulated by the degree of destruction of the third (Figure 3) body (the unit, multiple, narrow strip, and whole area).

discontinuous third body. The first stage is characterized by the minimal wear rate and stable friction factor. The second stage is characterized by the small constant and variable components of the friction coefficient. In terms of tribological characteristics, stages 1 and 2 indicate the acceptable working conditions of the tribological system. In contrast to this, stage 3 is characterized by the sharp increase of the constant and variable components of the friction coefficient, wear rate ("catastrophic wear"), vibrations, and noise, and operation in this zone is not

Dependence of the coefficient of friction (f) on the relative sliding (ε) and expected kind of surface damage.

Influence of Tribological Parameters on the Railway Wheel Derailment

DOI: http://dx.doi.org/10.5772/intechopen.89135

The friction coefficient is minimum and stable in the first and second zones, and its value depends mainly on the rheological properties of the third body. In the third zone, the friction coefficient is sharply increased and instable, and its value depends on the working conditions and properties of the surfaces, friction modifiers, and environment. The signs of the beginning of the third body are instability of the friction (coefficient) moment, vibrations, and noise, and at visual observation in the laboratory conditions, the signs of scuffing are noticeable. Its prediction is possible with the use of the tables and graphs considering the given friction modifier, working conditions and environment properties, as well as the criterion of

3. Some geometrical peculiarities of the wheel and rail interaction

.

The geometrical features of the wheel and rail interaction are stipulated by the designs of the rail track/bogie, wheel/rail, and their technical state. At lateral displacement of the wheelset relative to the rail, a contact point from the tread surfaces passes on the wheel flange root and rail corner, and the wheel and rail tread surfaces separate from each other. At further lateral displacement of the wheelset, the contact point passes on their steering surfaces, and the angle of inclination of the

It is difficult to predict and control the friction forces, wear rate of various types, vibrations, and noise of the heavy loaded interacting surfaces of the railway transport running gear that decreases traffic safety, increases energy loses on friction, etc. Many works are devoted to the researches of dependences of the tribological

admissible.

Figure 4.

destruction of the third body [26].

wheel flange increases up to 70°

209

Therefore, for ensuring the high wear resistance and stable friction force in the contact zone of the wheels and rails, it is necessary to provide continuous film of the third body with due properties between interacting surfaces. Consequently, a condition of destruction of the third body can be used as basics for estimation of the friction coefficient and the damages for the given peculiarities of the surface materials.

The various dominant damage types, wear rate, and friction coefficient are characteristic for various relative sliding. In Figure 4 is shown dependence of the friction coefficient on the relative sliding and expected kind of surface damage. Three zones can be distinguished in Figure 4. In zone 1 and at the beginning of zone 2, deformations of the subsurface layers reach the maximum values, and the interacting surfaces undergo cyclic deformations. With the rise of relative sliding, the contact temperature gradually increases, decreasing viscosity of the third body [24] and the friction factor that reaches the minimum value. At full separation of the interacting surfaces by the third body, the tribo-technical properties of the contact zone mainly depend on the properties of the third body, and they provide high wear resistance of the interacting surfaces and relatively stable friction coefficient.

In zone 2 the separate small impulses of the friction moment and adhesive wear of low intensity correspond to destruction of the third body in the separate unit and multiple places, and balance between destruction and restoration of the third body is observed that stipulates the "mild" and "sever" wear [25]. In zone 3 destruction of the third body takes place in the narrow strips that passes then into whole area of interacting surfaces, resulting in rise of the friction coefficient, its instability, wear rate (reaching "catastrophic" wear), and scuffing.

So, we have three stages of variation of the friction coefficient and wear: at continuous third body, at reversible discontinuous third body, and at irreversible Influence of Tribological Parameters on the Railway Wheel Derailment DOI: http://dx.doi.org/10.5772/intechopen.89135

#### Figure 4.

The further extension of destruction of the third body in the multiple places leads to the multiple damage of the third body, multiple adhesive junctions of micro-asperities, disruption of these junctions, and comparatively increased

The stages of damage of the interacting surfaces due to seizures and scuffing of the surfaces: (a) unit seizures, (b) multiple seizures, (c) seizures in the form of the narrow strip, and (d) seizures on the whole area of the roller.

A progression of the third body destruction leads to spacious, discontinuous third body, adhesive junctions of micro-asperities, disruption of these junctions, and increase of the friction forces ("positive friction"). As it is seen from Figure 2, negative, neutral, and positive behaviors of the friction forces are stipulated by the degree of destruction of the third (Figure 3) body (the unit, multiple, narrow strip,

Therefore, for ensuring the high wear resistance and stable friction force in the contact zone of the wheels and rails, it is necessary to provide continuous film of the third body with due properties between interacting surfaces. Consequently, a condition of destruction of the third body can be used as basics for estimation of the friction coefficient and the damages for the given peculiarities of the surface

The various dominant damage types, wear rate, and friction coefficient are characteristic for various relative sliding. In Figure 4 is shown dependence of the friction coefficient on the relative sliding and expected kind of surface damage. Three zones can be distinguished in Figure 4. In zone 1 and at the beginning of zone 2, deformations of the subsurface layers reach the maximum values, and the interacting surfaces undergo cyclic deformations. With the rise of relative sliding, the contact temperature gradually increases, decreasing viscosity of the third body [24] and the friction factor that reaches the minimum value. At full separation of the interacting surfaces by the third body, the tribo-technical properties of the contact zone mainly depend on the properties of the third body, and they

provide high wear resistance of the interacting surfaces and relatively stable friction

So, we have three stages of variation of the friction coefficient and wear: at continuous third body, at reversible discontinuous third body, and at irreversible

rate (reaching "catastrophic" wear), and scuffing.

In zone 2 the separate small impulses of the friction moment and adhesive wear of low intensity correspond to destruction of the third body in the separate unit and multiple places, and balance between destruction and restoration of the third body is observed that stipulates the "mild" and "sever" wear [25]. In zone 3 destruction of the third body takes place in the narrow strips that passes then into whole area of interacting surfaces, resulting in rise of the friction coefficient, its instability, wear

impulses of the friction moment and to "neutral friction."

Transportation Systems Analysis and Assessment

and whole area).

materials.

Figure 3.

coefficient.

208

Dependence of the coefficient of friction (f) on the relative sliding (ε) and expected kind of surface damage.

discontinuous third body. The first stage is characterized by the minimal wear rate and stable friction factor. The second stage is characterized by the small constant and variable components of the friction coefficient. In terms of tribological characteristics, stages 1 and 2 indicate the acceptable working conditions of the tribological system. In contrast to this, stage 3 is characterized by the sharp increase of the constant and variable components of the friction coefficient, wear rate ("catastrophic wear"), vibrations, and noise, and operation in this zone is not admissible.

The friction coefficient is minimum and stable in the first and second zones, and its value depends mainly on the rheological properties of the third body. In the third zone, the friction coefficient is sharply increased and instable, and its value depends on the working conditions and properties of the surfaces, friction modifiers, and environment. The signs of the beginning of the third body are instability of the friction (coefficient) moment, vibrations, and noise, and at visual observation in the laboratory conditions, the signs of scuffing are noticeable. Its prediction is possible with the use of the tables and graphs considering the given friction modifier, working conditions and environment properties, as well as the criterion of destruction of the third body [26].
