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Resource-saving management on sections of high-speed railway lines
Available online at www.sciencedirect.com Available online at www.sciencedirect.com
ScienceDirect ScienceDirect
Procediaonline Computer Science 00 (2019) 000–000 Available at www.sciencedirect.com Procedia Computer Science 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Computer Science 149 (2019) 297–300
ICTE in Transportation and Logistics 2018 (ICTE 2018) ICTE in Transportation and Logistics 2018 (ICTE 2018)
Resource-saving management on sections Resource-saving management on sections of high-speed railway lines of high-speed railway lines
Alina Romanovaa,a,*, Yury Luzhnovbb, Alexander Vygnanovaa, Elena Sokolovaaa, Natalya c Alina Romanova *, Yury Luzhnov ,Ivashkovska Alexander Vygnanov , Elena Sokolova , Natalya c Ivashkovska a a
Russian University of Transport, Obrazcova str.9,b.9, Moscow, 127994, Russia b JSC “VNIIZhT” RailwayObrazcova Research Institute, Russian University of Transport, str.9,b.9, Moscow, Moscow, Russia 127994, Russia c b Riga University, Kalku street, Riga,Moscow, LV-1658, Latvia JSCTechnical “VNIIZhT” Railway 1Research Institute, Russia c Riga Technical University, 1 Kalku street, Riga, LV-1658, Latvia
Abstract Abstract The problems of resource saving are formulated and the characteristic of frictional processes in the "wheel-rail" system on The problems of resource saving formulated and the characteristic of frictional processes "wheel-rail" system on sections of high-speed railway linesare is given. The materials of the article are based on the results in of the many years of work carried sections of high-speed railway lines is given. The materials of the article are based on the results of many years of work carried out within the framework of planned research conducted in Russian university of Transport (RUT (MIIT)), Mechanical out within the framework of ofplanned research conducted in Russian university of Transport (RUT (MIIT)), Engineering Research Institute the Russian Academy of Sciences (IMASH RAN), JSC VNIIZhT (Railway ResearchMechanical Institute). Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN), JSC VNIIZhT (Railway Research Institute). © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. by Elsevier B.V. This is an open accessPublished article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the the ICTE in in Transportation Transportationand andLogistics Logistics2018 2018(ICTE2018). (ICTE2018). Peer review under responsibility of the scientific committee of ICTE Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018). Keywords: High-speed highways; Resource saving; Frictional processes; "Wheel-rail" system Keywords: High-speed highways; Resource saving; Frictional processes; "Wheel-rail" system
1. Introduction 1. Introduction The work of the wheel-rail friction unit is extremely stressful, and the quality of its work is largely determined by workand of the wheel-rail friction unit is extremely stressful,and andeconomic the quality of its work is largely by theThe volume speed of the transported goods, many technical indicators, traffic safetydetermined and a number the volume and speed of the transported goods, many technical and economic indicators, traffic safety and a number of other related indicators of railway transport. of other related indicators of railway transport. The problem of wheel-rail coupling has been the focus of specialists’ attention since the inception of railway The problem of wheel-rail coupling has been the focusfor of the specialists’ attention since the inception railway transport. With the change in the company's requirements performance of railway transport, the of wheel-rail transport. With the change in the company's requirements for the performance of railway transport, the wheel-rail * Corresponding author. Tel.: +79169626888. E-mail address:author. [email protected] * Corresponding Tel.: +79169626888. E-mail address: [email protected] 1877-0509 © 2019 The Authors. Published by Elsevier B.V. This is an open access under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) 1877-0509 © 2019 Thearticle Authors. Published by Elsevier B.V. Peer is review under responsibility ofthe theCC scientific committee the ICTE in Transportation and Logistics 2018 (ICTE2018). This an open access article under BY-NC-ND licenseof(http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018).
1877-0509 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018). 10.1016/j.procs.2019.01.138
298 2
Alina Romanova et al. / Procedia Computer Science 149 (2019) 297–300 Author name / Procedia Computer Science 00 (2019) 000–000
friction unit was improved accordingly (material, construction, geometry of wheels and rails were selected, other parameters of the track and rolling stock were improved). Extremely urgent problem of work the wheel-rail friction unit remains today. Recently, on several roads in the world, especially with the development of high-speed traffic, the issue of undercut of the ridges of the wheels of the rolling stock and the side surface of the rails has become acute. This problem has become extremely acute in the last decade on the Russian Railways. This problem is exacerbated by the fact that the catastrophic wear of wheels and rails on the Railways of Russia is observed despite train traffic at relatively low speeds and with the decline in the total volume of transportation work and a monotonous increase in the specific energy consumption and fuel spent on the movement of trains. High-speed passenger lines are being introduced in Russia. The country's economy is emerging from the crisis, and the volume of transportations can significantly increase in the coming years. In this regard, the problem of clutch and, especially, increased wear process of wheels and rails in the coming years may become even more acute. To the material of the wheels of the rolling stock and rails is the subject with high requirements for resistance to contact fatigue, crumpling, brittle destruction, minimizing the possible negative impact on the counter body and enough workability. An attempt to find solutions to the problem of wear resistance of wheels and rails based only on the volume mechanical properties of their material and the results obtained only in laboratory tests is ineffective [1,2]. Without taking into account the processes of friction modeling and thermal dynamics of friction, these results cannot be directly transferred to real wheels [1, 2]. Among these results, the widely variable lubrication of the side surfaces of the wheels and rails has not yet led to a noticeable decrease in the intensity of their wear, but at the same time contributed to a sharp increase in the number of wheel and rail rejects along the slats [1, 2]. A significant reduction in the number of damage to the wheels and rails has not yet occurred. The question of the physical nature of this phenomenon and the reasons for the sharp increase in wear of wheels and rails remains unresolved [2] and, mainly, because the specialists involved in solving these problems, little use of the already accumulated knowledge of the nature of friction interaction of wheels and rails, as well as achievements in tribotechnics and thermal dynamics of friction [2]. 2. Friction interaction of wheels with rails and their wear The nature of the friction interaction of wheels with rails, lying in the basis of their wear, usually estimated from the time of the authors, such as N. P. Petrov, A. M. Babichkova, D.K. Minowa, etc. on the coefficient of traction rolling stock with rails ψсц. This coefficient is the ratio of the maximum realized at a certain moment of traction or braking force Fcy to the normal load Pa in relation to the support surface of the rail:
сц Fсц / Pa
(1)
Previously, the support surface was located mainly on the top of the rail head. But due to the fact that the vehicles have wheels with deviations of geometrical parameters (under normal loads) that can have an impact on the source of the friction condition of the friction surfaces, the coefficient of adhesion of vehicle can be represented as:
сц ск 0 о дин
(2)
where: ψо -the main coefficient of adhesion of the limiting axis, depending on the composition and surface properties of the friction surfaces of the wheels and rails; ηск – (UCS-slip) factor, taking into account the relative sliding of the friction surfaces, which determines the energy in the friction zone and the temperature of the friction surfaces and changes in their properties; ηо -the main coefficient of coupling weight of the locomotive (car), taking into account the influence of structural imperfections between the axes, leading to divergence of vertical, traction and brake loads; ηдин -dynamic coefficient of use of the coupling weight of the vehicle, associated with the characteristics of its movement.
Alina Romanova et al. / Procedia Computer Science 149 (2019) 297–300 Author name / Procedia Computer Science 00 (2019) 000–000
299 3
The coefficients, ηск, ηо, ηдин, characterizing the influence of rolling stock design features and the rail track, and keeping the train on the realization of limiting factor are often combined and referred them to the result of coupling weight usage.
сц 0
(3)
According to some authors =0,650,98. Its greatest values are realized only at the beginning of the movement of vehicles. The lowest - at high speeds. The analysis of works on the study of coefficients of adhesion, performed in different countries, allowed identifying 20 factors that affect the basic coefficient of adhesion of wheels - rails. Among them, the leaders were: the specific load in the area of contact between the wheel and the rail, the physical and chemical friction properties of the surface layers of dirt, the speed of sliding wheels on the rails, the preliminary wheel grip relative to the rail (determining the tribological characteristics of the surface layers), the surface hardness of the rubbing bodies and the speed of the vehicle. This approach allows us to identify the factors that have a direct impact on friction and wear, and to analyze the mechanism of occurrence and development of factors that directly lead to catastrophic wear of wheels and rails. As it is known, external and internal friction always transforms mechanical energy into thermal energy. The proportion of such conversion in friction without lubricating material (LM) can reach 98 %. Therefore, the processes of physical and chemical mechanics, which are implemented in friction, are significantly dependent on the thermal and temperature conditions generated by friction. Thus, the famous triad by Prof. I. V. Kragelsky: interaction of surfaces of solids, changes in the properties of contacting materials and, finally, the destruction of surfaces because of previous stages (i.e. wear process) must necessarily take into account thermal and temperature factors. As follows from the molecular-mechanical theory of external friction and fatigue theory of wear of solids [2], friction-wear characteristics and mechanical properties of materials of friction pairs are related by various nonlinear functional dependencies, moreover these dependences can vary significantly from friction modes and, first of all, from thermal and temperature, the strength properties of materials are very dependent on temperature, the influence of the load and the speed (number of cycles) of loading is much less. It is clearly seen that in certain temperature ranges, the hardness of materials can be reduced many times, becoming minimal, approaching the melting temperature. At such temperatures, the friction contact becomes plastic, and the actual contact area of the Аr, even with a small load of the рa, increases sharply, approaching the contour Аc and further to the nominal Аa [2]. In the conditions of lubrication, when the mode of liquid friction (hydrodynamic or elastohydrodynamic) is realized, the effect of the temperature factor is associated with the permissible operating temperature of the lubricant, which should not exceed the critical volumetric decomposition and ignition temperature of the material, so that there is no spontaneous transition first to the boundary, and then to friction without LM with all the ensuing negative phenomena in the form of a sharp increase in the coefficient of friction, then the temperature, the occurrence of bullying, great wear and even the jamming of the friction unit. The situation is somewhat different when it comes to the boundary lubrication regime. It is necessary to take into account the processes of physical and chemical mechanics that occur in thin boundary layers. In this regard, a typical diagram of the coefficient of friction change from the temperature of the friction surface θ at the boundary lubrication differs significantly from the dependences of friction without lubricating material (LM), both in the nature of the change and in the value of the coefficient of friction and temperature (they are much lower). In heavily loaded friction units the temperature in the contact zones can reach very high values (above 1000 °C), which leads to the melting of metal and decomposition of non-metallic materials. The intensity of deformation and temperature of the surface layers decreases in depth, and the temperature gradient in such conditions can reach 8001000 °C / mm. Since it is practically impossible (and impractical) to use the same pair of friction at small and large surface and volume temperatures, all friction units are divided, depending on the friction surface temperatures, into five groups:
Alina Romanova et al. / Procedia Computer Science 149 (2019) 297–300 Author name / Procedia Computer Science 00 (2019) 000–000
300 4
very light - up to 100 °C, light - up to 250 °C, medium-up to 600 °C, heavy-up to 1000 °C, super-heavy - more than 1000 °C. In practice, there may be cases when only one temperature gradient in the surface layers of the elements of the friction pair causes such temperature stresses that friction is carried out during plastic contact even when the volume temperature is small, and the nominal pressures can cause only elastic deformation. Thermal stresses of this type contribute to the formation of cracks and lead to serious wear and tear. Thus, in addition to the General weakening action, high temperatures and temperature gradients in some structures (for example, drums, disks, bushings, etc.) are also present. e.) cause such surface stresses, which are much higher than the stresses of the friction forces. Materials of friction pairs under high stresses reduce the friction force and increase wear. The stresses in the surface layer depend on the properties of materials, macro - and micro-geometry of the contact zone. They usually prevail over the stresses in the volume of the friction pair elements, most of which depend on temperature gradients, and not on mechanical quantities [1]. Chemical and structural changes in materials are caused by the interaction of materials with each other and the environment, as well as temperature. Depending on the conditions and mode of operation of the bulk temperature in the friction pairs are significantly different. 3. Conclusion On the basis of the earlier performed work, it can be concluded that:
The level of friction and wear intensity of wheels and rails depend mainly on the temperature and properties of the thin surface layer of rubbing bodies in a wide temperature range. These temperatures are quite real for railway transport and have their maximum and minimum values. Bulk mechanical properties and temperature in the considered cases play only the role of amendments to what is happening in the contact zone of the wheel and the rail to actual processes Thermal dynamics of friction based on the identified physical-chemical ideas about the interaction and the laws of changes in the friction characteristics of the friction tracks will allow to clarify the nature of catastrophic wear of wheels and rails and to suggest the effective ways of dealing with it
With the limitation of high-speed movement (HSM), the process of development of temperature voltage is further enhanced due to temperature processes. Increased wear, loss in the wheel-rail system reduced gravity. Thus, when assessing the effectiveness of HSM, it is necessary to take into account these components of losses, which grow in proportion to the square of the speed, as the assessment in the first diligence shows. Acknowledgements The materials of the article are based on the results of many years of work carried out within the framework of planned research conducted in Russian university of Transport (RUT (MIIT)), Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN), JSC VNIIZhT (Railway Research Institute). References [1] Luzhnov, Yu. (2003) Adhesion Wheels with Rails. Moscow: Intext, 143. [2] Chichinadze, A. (2001) Basics of Tribology. Moscow: Machine Building, 642.
ScienceDirect ScienceDirect
Procediaonline Computer Science 00 (2019) 000–000 Available at www.sciencedirect.com Procedia Computer Science 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Computer Science 149 (2019) 297–300
ICTE in Transportation and Logistics 2018 (ICTE 2018) ICTE in Transportation and Logistics 2018 (ICTE 2018)
Resource-saving management on sections Resource-saving management on sections of high-speed railway lines of high-speed railway lines
Alina Romanovaa,a,*, Yury Luzhnovbb, Alexander Vygnanovaa, Elena Sokolovaaa, Natalya c Alina Romanova *, Yury Luzhnov ,Ivashkovska Alexander Vygnanov , Elena Sokolova , Natalya c Ivashkovska a a
Russian University of Transport, Obrazcova str.9,b.9, Moscow, 127994, Russia b JSC “VNIIZhT” RailwayObrazcova Research Institute, Russian University of Transport, str.9,b.9, Moscow, Moscow, Russia 127994, Russia c b Riga University, Kalku street, Riga,Moscow, LV-1658, Latvia JSCTechnical “VNIIZhT” Railway 1Research Institute, Russia c Riga Technical University, 1 Kalku street, Riga, LV-1658, Latvia
Abstract Abstract The problems of resource saving are formulated and the characteristic of frictional processes in the "wheel-rail" system on The problems of resource saving formulated and the characteristic of frictional processes "wheel-rail" system on sections of high-speed railway linesare is given. The materials of the article are based on the results in of the many years of work carried sections of high-speed railway lines is given. The materials of the article are based on the results of many years of work carried out within the framework of planned research conducted in Russian university of Transport (RUT (MIIT)), Mechanical out within the framework of ofplanned research conducted in Russian university of Transport (RUT (MIIT)), Engineering Research Institute the Russian Academy of Sciences (IMASH RAN), JSC VNIIZhT (Railway ResearchMechanical Institute). Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN), JSC VNIIZhT (Railway Research Institute). © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. by Elsevier B.V. This is an open accessPublished article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the the ICTE in in Transportation Transportationand andLogistics Logistics2018 2018(ICTE2018). (ICTE2018). Peer review under responsibility of the scientific committee of ICTE Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018). Keywords: High-speed highways; Resource saving; Frictional processes; "Wheel-rail" system Keywords: High-speed highways; Resource saving; Frictional processes; "Wheel-rail" system
1. Introduction 1. Introduction The work of the wheel-rail friction unit is extremely stressful, and the quality of its work is largely determined by workand of the wheel-rail friction unit is extremely stressful,and andeconomic the quality of its work is largely by theThe volume speed of the transported goods, many technical indicators, traffic safetydetermined and a number the volume and speed of the transported goods, many technical and economic indicators, traffic safety and a number of other related indicators of railway transport. of other related indicators of railway transport. The problem of wheel-rail coupling has been the focus of specialists’ attention since the inception of railway The problem of wheel-rail coupling has been the focusfor of the specialists’ attention since the inception railway transport. With the change in the company's requirements performance of railway transport, the of wheel-rail transport. With the change in the company's requirements for the performance of railway transport, the wheel-rail * Corresponding author. Tel.: +79169626888. E-mail address:author. [email protected] * Corresponding Tel.: +79169626888. E-mail address: [email protected] 1877-0509 © 2019 The Authors. Published by Elsevier B.V. This is an open access under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) 1877-0509 © 2019 Thearticle Authors. Published by Elsevier B.V. Peer is review under responsibility ofthe theCC scientific committee the ICTE in Transportation and Logistics 2018 (ICTE2018). This an open access article under BY-NC-ND licenseof(http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018).
1877-0509 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018). 10.1016/j.procs.2019.01.138
298 2
Alina Romanova et al. / Procedia Computer Science 149 (2019) 297–300 Author name / Procedia Computer Science 00 (2019) 000–000
friction unit was improved accordingly (material, construction, geometry of wheels and rails were selected, other parameters of the track and rolling stock were improved). Extremely urgent problem of work the wheel-rail friction unit remains today. Recently, on several roads in the world, especially with the development of high-speed traffic, the issue of undercut of the ridges of the wheels of the rolling stock and the side surface of the rails has become acute. This problem has become extremely acute in the last decade on the Russian Railways. This problem is exacerbated by the fact that the catastrophic wear of wheels and rails on the Railways of Russia is observed despite train traffic at relatively low speeds and with the decline in the total volume of transportation work and a monotonous increase in the specific energy consumption and fuel spent on the movement of trains. High-speed passenger lines are being introduced in Russia. The country's economy is emerging from the crisis, and the volume of transportations can significantly increase in the coming years. In this regard, the problem of clutch and, especially, increased wear process of wheels and rails in the coming years may become even more acute. To the material of the wheels of the rolling stock and rails is the subject with high requirements for resistance to contact fatigue, crumpling, brittle destruction, minimizing the possible negative impact on the counter body and enough workability. An attempt to find solutions to the problem of wear resistance of wheels and rails based only on the volume mechanical properties of their material and the results obtained only in laboratory tests is ineffective [1,2]. Without taking into account the processes of friction modeling and thermal dynamics of friction, these results cannot be directly transferred to real wheels [1, 2]. Among these results, the widely variable lubrication of the side surfaces of the wheels and rails has not yet led to a noticeable decrease in the intensity of their wear, but at the same time contributed to a sharp increase in the number of wheel and rail rejects along the slats [1, 2]. A significant reduction in the number of damage to the wheels and rails has not yet occurred. The question of the physical nature of this phenomenon and the reasons for the sharp increase in wear of wheels and rails remains unresolved [2] and, mainly, because the specialists involved in solving these problems, little use of the already accumulated knowledge of the nature of friction interaction of wheels and rails, as well as achievements in tribotechnics and thermal dynamics of friction [2]. 2. Friction interaction of wheels with rails and their wear The nature of the friction interaction of wheels with rails, lying in the basis of their wear, usually estimated from the time of the authors, such as N. P. Petrov, A. M. Babichkova, D.K. Minowa, etc. on the coefficient of traction rolling stock with rails ψсц. This coefficient is the ratio of the maximum realized at a certain moment of traction or braking force Fcy to the normal load Pa in relation to the support surface of the rail:
сц Fсц / Pa
(1)
Previously, the support surface was located mainly on the top of the rail head. But due to the fact that the vehicles have wheels with deviations of geometrical parameters (under normal loads) that can have an impact on the source of the friction condition of the friction surfaces, the coefficient of adhesion of vehicle can be represented as:
сц ск 0 о дин
(2)
where: ψо -the main coefficient of adhesion of the limiting axis, depending on the composition and surface properties of the friction surfaces of the wheels and rails; ηск – (UCS-slip) factor, taking into account the relative sliding of the friction surfaces, which determines the energy in the friction zone and the temperature of the friction surfaces and changes in their properties; ηо -the main coefficient of coupling weight of the locomotive (car), taking into account the influence of structural imperfections between the axes, leading to divergence of vertical, traction and brake loads; ηдин -dynamic coefficient of use of the coupling weight of the vehicle, associated with the characteristics of its movement.
Alina Romanova et al. / Procedia Computer Science 149 (2019) 297–300 Author name / Procedia Computer Science 00 (2019) 000–000
299 3
The coefficients, ηск, ηо, ηдин, characterizing the influence of rolling stock design features and the rail track, and keeping the train on the realization of limiting factor are often combined and referred them to the result of coupling weight usage.
сц 0
(3)
According to some authors =0,650,98. Its greatest values are realized only at the beginning of the movement of vehicles. The lowest - at high speeds. The analysis of works on the study of coefficients of adhesion, performed in different countries, allowed identifying 20 factors that affect the basic coefficient of adhesion of wheels - rails. Among them, the leaders were: the specific load in the area of contact between the wheel and the rail, the physical and chemical friction properties of the surface layers of dirt, the speed of sliding wheels on the rails, the preliminary wheel grip relative to the rail (determining the tribological characteristics of the surface layers), the surface hardness of the rubbing bodies and the speed of the vehicle. This approach allows us to identify the factors that have a direct impact on friction and wear, and to analyze the mechanism of occurrence and development of factors that directly lead to catastrophic wear of wheels and rails. As it is known, external and internal friction always transforms mechanical energy into thermal energy. The proportion of such conversion in friction without lubricating material (LM) can reach 98 %. Therefore, the processes of physical and chemical mechanics, which are implemented in friction, are significantly dependent on the thermal and temperature conditions generated by friction. Thus, the famous triad by Prof. I. V. Kragelsky: interaction of surfaces of solids, changes in the properties of contacting materials and, finally, the destruction of surfaces because of previous stages (i.e. wear process) must necessarily take into account thermal and temperature factors. As follows from the molecular-mechanical theory of external friction and fatigue theory of wear of solids [2], friction-wear characteristics and mechanical properties of materials of friction pairs are related by various nonlinear functional dependencies, moreover these dependences can vary significantly from friction modes and, first of all, from thermal and temperature, the strength properties of materials are very dependent on temperature, the influence of the load and the speed (number of cycles) of loading is much less. It is clearly seen that in certain temperature ranges, the hardness of materials can be reduced many times, becoming minimal, approaching the melting temperature. At such temperatures, the friction contact becomes plastic, and the actual contact area of the Аr, even with a small load of the рa, increases sharply, approaching the contour Аc and further to the nominal Аa [2]. In the conditions of lubrication, when the mode of liquid friction (hydrodynamic or elastohydrodynamic) is realized, the effect of the temperature factor is associated with the permissible operating temperature of the lubricant, which should not exceed the critical volumetric decomposition and ignition temperature of the material, so that there is no spontaneous transition first to the boundary, and then to friction without LM with all the ensuing negative phenomena in the form of a sharp increase in the coefficient of friction, then the temperature, the occurrence of bullying, great wear and even the jamming of the friction unit. The situation is somewhat different when it comes to the boundary lubrication regime. It is necessary to take into account the processes of physical and chemical mechanics that occur in thin boundary layers. In this regard, a typical diagram of the coefficient of friction change from the temperature of the friction surface θ at the boundary lubrication differs significantly from the dependences of friction without lubricating material (LM), both in the nature of the change and in the value of the coefficient of friction and temperature (they are much lower). In heavily loaded friction units the temperature in the contact zones can reach very high values (above 1000 °C), which leads to the melting of metal and decomposition of non-metallic materials. The intensity of deformation and temperature of the surface layers decreases in depth, and the temperature gradient in such conditions can reach 8001000 °C / mm. Since it is practically impossible (and impractical) to use the same pair of friction at small and large surface and volume temperatures, all friction units are divided, depending on the friction surface temperatures, into five groups:
Alina Romanova et al. / Procedia Computer Science 149 (2019) 297–300 Author name / Procedia Computer Science 00 (2019) 000–000
300 4
very light - up to 100 °C, light - up to 250 °C, medium-up to 600 °C, heavy-up to 1000 °C, super-heavy - more than 1000 °C. In practice, there may be cases when only one temperature gradient in the surface layers of the elements of the friction pair causes such temperature stresses that friction is carried out during plastic contact even when the volume temperature is small, and the nominal pressures can cause only elastic deformation. Thermal stresses of this type contribute to the formation of cracks and lead to serious wear and tear. Thus, in addition to the General weakening action, high temperatures and temperature gradients in some structures (for example, drums, disks, bushings, etc.) are also present. e.) cause such surface stresses, which are much higher than the stresses of the friction forces. Materials of friction pairs under high stresses reduce the friction force and increase wear. The stresses in the surface layer depend on the properties of materials, macro - and micro-geometry of the contact zone. They usually prevail over the stresses in the volume of the friction pair elements, most of which depend on temperature gradients, and not on mechanical quantities [1]. Chemical and structural changes in materials are caused by the interaction of materials with each other and the environment, as well as temperature. Depending on the conditions and mode of operation of the bulk temperature in the friction pairs are significantly different. 3. Conclusion On the basis of the earlier performed work, it can be concluded that:
The level of friction and wear intensity of wheels and rails depend mainly on the temperature and properties of the thin surface layer of rubbing bodies in a wide temperature range. These temperatures are quite real for railway transport and have their maximum and minimum values. Bulk mechanical properties and temperature in the considered cases play only the role of amendments to what is happening in the contact zone of the wheel and the rail to actual processes Thermal dynamics of friction based on the identified physical-chemical ideas about the interaction and the laws of changes in the friction characteristics of the friction tracks will allow to clarify the nature of catastrophic wear of wheels and rails and to suggest the effective ways of dealing with it
With the limitation of high-speed movement (HSM), the process of development of temperature voltage is further enhanced due to temperature processes. Increased wear, loss in the wheel-rail system reduced gravity. Thus, when assessing the effectiveness of HSM, it is necessary to take into account these components of losses, which grow in proportion to the square of the speed, as the assessment in the first diligence shows. Acknowledgements The materials of the article are based on the results of many years of work carried out within the framework of planned research conducted in Russian university of Transport (RUT (MIIT)), Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN), JSC VNIIZhT (Railway Research Institute). References [1] Luzhnov, Yu. (2003) Adhesion Wheels with Rails. Moscow: Intext, 143. [2] Chichinadze, A. (2001) Basics of Tribology. Moscow: Machine Building, 642.