China
Africa
Explore chapters and articles related to this topic
Effect of laser energy density on microstructure and properties of SLM 24CrNiMoY alloy steel
Published in Domenico Lombardo, Ke Wang, Advances in Materials Science and Engineering, 2021
M. Sun, S.Y. Chen, M.W. Wei, X.W. Song, L. Zhou, M. Wang
The high-speed railway brake disc is one of the key parts to ensure the safe operation of high-speed railway. The traditional manufacturing method of brake disc is mainly casting heating treatment, which has a long process cycle and needs to improve the product performance [1]. With the rapid development of laser additive manufacturing technology, it has become one of the hot topics in recent years to study the preparation of large-scale and complex high-speed railway brake discs by selective laser melting (SLM) [2–5]. High speed railway brake discs are mainly made of 24CrNiMoY alloy steel. Based on the non-equilibrium solidification characteristics of SLM alloy steel, scholars around the world have studied the preparation of 24CrNiMoY alloy steel by SLM, the microstructure and properties of it have been deeply studied, while some important progress and achievements have been made [6–11]. These studies have established a good theoretical and technical basis for the microstructure evolution control properties of 24CrNiMoY alloy steel prepared by SLM. However, it is a complex non-equilibrium metallurgical process to produce alloy steel high-speed rail brake disc by SLM, while the influence of laser processing parameters on the microstructure, defects and properties of the formed alloy steel is deterministic. How to obtain 24CrNiMoY alloy steel samples with good properties (tensile strength > 1150 MPa, elongation of 10–12%, hardness of 340–350 HV0.2) by SLM equipment is still one of the technical problems.
Friction and Wear in Extreme Conditions
Published in Ahmed Abdelbary, Extreme Tribology, 2020
In the winter of 2017, several incidents regarding the stopping distance of freight wagons equipped with composite brake blocks occurred in the north of Sweden at temperatures as low as −10ºC. It seems as if the friction coefficient of composite brake blocks decreases considerably at low temperatures, resulting in a prolonged braking distance and near misses. A similar scenario has also been noticed in Finland. A study by Lyu et al. (Lyu et al., 2019) addresses the difference in friction and wear from cast iron, sinter and composite railway brake blocks at low ambient temperatures. In this study, three different railway brake block materials, cast iron, sinter and composite, were investigated. Brake specimens were tested at five different temperature levels: 10ºC, 3ºC, −10ºC, −20ºC and −30ºC. Figure 8.22 indicates that the cast iron brake block has a transition in friction coefficient with the decreasing temperature from 10ºC to −30ºC. At −10ºC and −20ºC, the friction coefficient of a cast iron brake block is much lower than at the other three temperatures. The composite brake block has the lowest friction coefficient at all five temperatures. It may also be noted that the friction coefficient of the composite brake block decreases rapidly in subzero temperatures. For the sinter brake block, the friction coefficient remains stable at all five temperatures and seems not to be sensitive to the change of temperature. It is demonstrated that the composite brake material contains a large portion of a phenolic resin, which is prone to adsorbing water vapor. The adsorbed water vapor forms an ice condensation layer on the composite brake block, which will act as a lubricant and reduce the friction coefficient.
Dynamic simulation of a heavy-haul freight car under abnormal braking application on tangent and curve
Published in Vehicle System Dynamics, 2022
P. H. A. Corrêa, P. G. Ramos, L. H. S. Teixeira, G. F. M. dos Santos, A. A. dos Santos
Braking is a critical aspect of railway train operations. Railway brakes are composed mainly of air brake which relies on pressurised air to push brake shoes or pads against wheel treads [12]. Braking and traction forces are not explicitly considered in most of the train dynamics simulation software, as their primary focus is to provide a platform for long-distance simulations with real-time scenarios, which demands fast-solution algorithms. These packages consider the braking scenarios through the definition of a speed profile given by the user. Additionally, other parameters, including the primary and secondary suspension responses, are also sensitive to the resulting speed profile although this effect might not be evaluated [1].