Search Results (21)

As a key component of the train braking system, the comprehensive performance of brake discs plays a vital role in ensuring the operational safety of trains. With the advent of high-speed and heavy-haul trains, the thermal energy generated by braking systems has significantly increased. The resulting rapid temperature rise can easily exceed the material limits of brake discs. Consequently, research focused on enhancing brake disc performance in high-temperature environments, improving thermal fatigue resistance, and optimizing tribological properties has become increasingly critical. Brake disc materials have undergone substantial evolution, transitioning from traditional iron and steel to lightweight aluminum matrix composites and carbon matrix composites. While iron and steel benefit from mature manufacturing processes and proven reliability, their high mass density poses challenges in meeting the demands for lightweight and high-speed development in modern rail transit. Although aluminum matrix composites and carbon matrix composites offer advantages like low density and high heat capacity, they still face several technical challenges in practical applications. This paper outlines the key characteristics of train brake disc materials, emphasizing the application status and research progress of iron and steel, aluminum matrix composites, and carbon matrix composites. Additionally, it briefly introduces surface modification technologies for iron and steel brake discs, with the goal of providing insights and references to guide the innovation and development of train brake disc materials. Full article

Excessive friction at the wheel–rail contact can limit the lifespan of the wheels and rails. Meanwhile, insufficient friction can lead to increased braking distance, risking safety. Top-of-Rail (TOR) products are recognised for their potential to achieve intermediate friction levels at the wheel–rail contact and mitigate wear damages. However, the impact of these products on the airborne wear particles emitted from wheel–rail contact is not thoroughly evaluated. High particle concentration levels, particularly on underground train platforms, raise respiratory and cardiovascular health concerns. This research employs a pin-on-disc to study the effect of laboratory (environmentally acceptable) and commercial TOR products on friction, retentivity, wear, and airborne particle emissions at the wheel–rail interface. The results indicated that TOR products with higher retentivity offered a wider interval of desired intermediate friction levels. The TOR products significantly reduced particle emissions compared to the dry condition. TOR products can, therefore, be promising in controlling friction and mitigating wear and particle emissions at the wheel–rail interface. However, to achieve the benefits of these products, it is essential to tailor their chemical composition carefully. Full article

When a railway train runs along a curved track with braking, the dynamic behaviors of the vehicle are extremely complex and difficult to accurately reveal due to the coupling effects between the wheel–rail interactions and the disc–pad frictions. Therefore, a rigid–flexible coupled trailer car dynamics model of a railway train is established. In this model, the brake systems and vehicle system are dynamically coupled via the frictions within the braking interface, wheel–rail relationships and suspension systems. Furthermore, the effectiveness of the established model is validated by a comparison with the field test data. Based on this, the dynamic response characteristics of vehicle under curve and straight braking conditions are analyzed and compared, and the influence of the curve geometric parameters on vehicle vibration and operation safety is explored. The results show that braking on a curve track directly affects the vibration characteristics of the vehicle and reduces its operation safety. When the vehicle is braking on a curve track, the lateral vibration of the bogie frame significantly increases compared to the vehicle braking on a straight track, and the vibration intensifies as the curve radius decreases. When the curved track maintains equilibrium superelevation, the differences in primary suspension force, wheel–rail vertical force, and wheel axle lateral force between the inner and outer sides of the first and second wheelsets are relatively minor under both straight and curved braking conditions. Additionally, under these circumstances, the derailment coefficient is minimized. However, when the curve radius is 7000 m, with a superelevation of 40 mm, the maximum dynamic wheel load reduction rate of the inner wheel of the second wheelset is 0.54, which reaches 90% of the allowable limit value of 0.6 for the safety index, and impacts the vehicle running safety. Therefore, it is necessary to focus on the operation safety of railway trains when braking on curved tracks. Full article

The thermal analysis of brake discs is crucial for studying issues such as wear and cracking. This paper establishes a symmetric two-dimensional brake disc model using the barycentric rational interpolation collocation method (BRICM). The model accounts for the effects of thermal radiation and is linearized using Newton’s linear iteration method. In the spatial dimension, the two-dimensional heat conduction equation is discretized using BRICM, while in the temporal dimension, it is discretized using the finite difference method (FDM). The resulting temperature distribution of the brake disc during two consecutive braking events is consistent with experimental data. Additionally, factors affecting the accurate calculation of the temperature are examined. Compared to other models, the proposed model achieves accurate temperature distributions with fewer nodes. Furthermore, the numerical results highlight the significance of thermal radiation within the model. The results obtained using BRICM can be used to predict the two-dimensional temperature distribution of train brake discs. Full article

This paper examines the effects of thermo-solid coupling and the influence of braking parameter changes on the vibration characteristics of high-speed train disc brakes. A multi-flexible body dynamics model of high-speed train disc brakes considering thermo-solid coupling was established to study the vibration characteristics of high-speed train disc brakes during service. The results show that the uneven distribution of temperature and stress produced during the brake disc’s service was the primary cause of the warping deformation of the brake disc, which prevented the brake disc and the brake pads from making sufficient contact and caused vibration while braking. By comparing the analytical findings of whether the model was subject to the coupling effect or not, the influence of thermo-solid coupling on the braking procedure was demonstrated from the standpoint of energy distribution. The severity of the high-speed train brake disc vibration gradually increased along with the braking pressure and initial speed. In addition, vibration aggravated the instability of the braking process, which could lead to thermoelastic instability and is harmful to the braking performance of the brake. These findings provide theoretical support for designing and manufacturing disc brakes for high-speed trains. Full article

The effectiveness of railway brakes strongly depends on their thermal condition. A computer simulation and experimental investigations on a full-scale dynamometric stand were chosen as an adequate analysis of the heat transfer process in brakes. The article introduces a two-dimensional, axisymmetric numerical model of the tested disc brake. Boundary conditions related to the heat generated in the friction brake and heat transferred to the environment are also presented. The transient heat transfer problem was solved using the in-house computer program of the finite element method. The article presents simulations and experimental investigations of the intensive braking of a train with an initial high speed. Temperature responses of the disc brake on the friction surface and at other selected points are shown. In addition, a thermal imaging camera was used to assess the temperature distribution on the friction surface of the disc. The results of experimental and simulation tests were preliminarily compared. Similar maximum temperature values were obtained at the end of braking with a particular discrepancy in temperature responses during the analyzed process. Full article

Matching analysis is a key step in the process of verifying the adaptation of carbon-ceramic brake discs to high-speed trains’ braking system. Relevant research on matching analysis tends to be carried out only on a single parameter of the brake disc. Due to this lack of comprehensive analysis, a data-driven, parametric method is proposed to address the problem. We have summarised the matching parameters of carbon-ceramic brake discs in three dimensions: assembly interface, physical characteristics, and braking performance. The method is based on the feasibility of modelling the parameters, completing the analysis of non-modelled parameters through a comparative conformity check, and modelling parameters through a statistical analysis of the experimental data. Conformity comparison results show that the example carbon-ceramic brake disc is well suited to high-speed trains and is better matching than the example cast-steel brake discs in terms of mass and average frictional coefficient. Analysis of the simulated experimental data shows that under high-speed braking conditions, the maximum disc surface temperature and wear of the example carbon-ceramic disc is higher than that of the cast-steel disc, trains equipped with carbon-ceramic discs have shorter emergency braking distances and higher average braking deceleration, and the carbon-ceramic discs exhibit better matching performance. Full article

Inspired by the difference in the friction radii of the pads from the high-speed train brake system, stick–slip experiments for a disc–block friction system with different friction radii were carried out via a test device. Based on the test results, the stick–slip vibration characteristics of the disc–block friction system with variation in the friction radius were analyzed, and the corresponding Stribeck model parameters in exponential and fractional forms were identified. The experimental results show that with an increase in the friction radius the vibration amplitude first increased and then decreased and the frequency of stick–slip vibration increased. The identified Stribeck model parameters show that the decay factors increased, the static friction coefficient decreased, and the dynamic friction coefficient decreased first and then increased as the friction radius increased. Moreover, the identified Stribeck model in an exponential form can more accurately reflect the stick–slip characteristics of a disc–block friction system than the model in a fractional form. It can be further applied in the investigation of the dynamic behaviors of high-speed train brake systems. Full article

In order to achieve the goal of lightening the braking system of urban rail trains, SiCp/ZL101 and ZL101 plates were welded by friction stir lap welding (FSLW) to prepare a new type of brake disc material. The friction and wear properties of the friction-stir-processed composite material were studied at different temperatures (30 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C) to provide a theoretical basis for the evaluation of braking performance. The experimental results showed that the sliding friction processes at each temperature were relatively stable, the friction coefficients did not vary much and the average friction coefficients changed slightly, stabilizing at about 0.4. The wear extent and the depth of wear scars increased with the increase in the temperature, reaching the highest at 150 °C and then began to decrease. At room temperature, the wear forms were mainly oxidative wear and abrasive wear; as the temperature rose, under the cyclic shearing action of the grinding ball, the abrasive debris fell off under the expansion of fatigue cracks and fatigue wear was the main form at this stage. When the temperature reached 200 °C, it began to show the characteristics of adhesive wear; after 250 °C, due to the gradual formation of a mechanical mixed layer containing more SiC particles and oxides on the wear surface, it exhibited high-temperature lubrication characteristics, and the wear extent was equivalent to 35% of the wear extent at normal temperature, indicating that the composite material had good high-temperature friction and wear properties. Full article

The pin on the disc friction tester was used to conduct the intermittent braking testing of train brake materials with a low-temperature environment simulation device at temperatures 20 °C, 0 °C, −10 °C, −20 °C, and −30 °C. The results show that intermittent braking presents different wear characteristics of braking materials at low temperatures. Under different ambient temperature conditions, the most volatile friction coefficient caused by intermittent braking happens at 0 °C, and the wear rate of brake materials reaches its maximum at 0 °C. The wear surface morphology of the brake pad material mainly includes scratches, furrows, adhesions, and abscission pits, while the surface of the brake disc material was dominated by scratches, furrows, and adhesions. With the decrease in temperature, the adhesion damage of the brake pad/disc material increases. At 0 °C, the brake pad material has crack damage. Full article

Cerebral palsy is a neurological disorder with a variety of symptoms that can affect muscle coordination and movement. Crouch gait is one such symptom that is defined as excessive knee flexion accompanied by a crouched posture. This paper introduces a passive exoskeleton to support the knee joint during stance of individuals with cerebral palsy that are affected by crouch gait. The exoskeleton utilizes a hydraulic disc brake mechanism that is actuated only by the body weight and gait of the wearer to provide a braking torque at the knee joint. This passive, gait-based control method aims to offer a compact, lightweight, and simple alternative to existing exoskeletons. Preliminary experiments were conducted to verify the mechanics, safety, and braking capabilities of the device with healthy participants. A pilot study with an individual with cerebral palsy was then conducted. The individual with cerebral palsy showed a reduction in hip joint angle when using the device (18.8${}^{\circ }$ and 21.7${}^{\circ }$ for left and right sides, respectively). The muscle co-activation index was also reduced from 0.48 to 0.24 on the right side and from 0.17 to 0.017 on the left side. However, changes such as activation timing and device training need to be improved to better support the user. Full article

For the unique structural characteristics of ventilated brake discs and the complex problem of energy conversion during braking, a calculation method for energy conversion of the ventilated brake disc based on simultaneous heat generation and heat dissipation is proposed. The transient heat transfer model of the ventilated brake disc for high-speed trains is established. Considering the control equations of heat generation–heat dissipation and plate–cylinder convection heat transfer, the virtual simulation of the energy change of the ventilated brake disc during the braking process is carried out. The temperature and stress distribution of contact friction surface and clearance structure of the ventilated brake disc are analysed from the perspective of function conversion. The results show that the heat generated by the ventilated brake disc increases nonlinearly, and the heat dissipated increases linearly. The heat of ventilated brake disc increases with the increase of braking time, but its growth rate decreases continuously. The maximum temperature of the ventilated brake disc is 268 °C, which appears on the friction surface. After braking, its heat is 6.636 × 10⁶ J. The analysis results and methods provide a basis for optimizing the structure of ventilated brake discs. Full article

Effective braking in high-speed trains is one of the major bottlenecks in expediting the technology and possibilities to improve speed. Although substantial progress has been made to increase operating speed, perhaps, thermal fatigue cracking in brake discs is a primary constraint so far. Thermal fatigue cracking is the major cause of brake disc failure in high-speed trains, especially trains with a speed of 350 km/h or above. In this study, new material composition is proposed for brake discs of high-speed trains. A comprehensive investigation is presented based on fatigue crack initiation and propagation, along with wear and micro-hardness characterization. Thermal fatigue tests at various thermal cycles between 20 ℃ and 700 ℃ were performed and the experimental results are compared with fatigue properties of a commercial brake disc material. An experimental trial revealed that thermal cracks normally initiate and propagate along the oxidized grain boundaries; nevertheless, crack propagation is restricted by the fine precipitates and lath structure of martensitic. Moreover, crack length at the initiation and propagation stage is predicted through crack growth rate and favorable grain size in the crack vicinity. Thermal fatigue life can be improved by dictating the microstructure and precipitate morphology of cast steel by tailoring the alloying composition. Full article

The stability and reliability of braking system are essential factors for the safe operation of high-speed trains. In the proposed work, tribological properties of a newly developed brake disc material namely BD-1 were studied considering the thermal-mechanical effects, as well as the evolutions of wear debris, were particularly examined. The tribological properties were also compared with an existing commercial brake disc material namely BD-2 in text. Friction and wear tests were carried out on BD-1 and BD-2 against a commercial brake pad material (BP) to simulate the real emergence braking conditions of a 350 km/h high-speed railway. The thermal-mechanical coupling effects of the friction velocity, wear mass, temperatures and the friction coefficient were investigated. Local wear track and wear debris were analyzed by using SEM and EDS. Results show that the shape and size of wear debris evolve as the dominant wear mechanism varies during braking tests. As the sliding speed increases from 250 to 1250 rpm, the debris may become fine particles, then into a mixture of lamellar shape and flake shape, and finally becomes fine particles again at high speed. The maximum size of wear debris is first from 20 μm to 65 μm, and then down to 10 μm. As the local area temperature increased by more than 400 °C, debris adhere to the surface forming an adhesive layer that may act as a lubricant. Debris may help to form an adhesive lubrication layer and undertake plastics defor-mation at the speed range of 500–1000 rpm. The local area temperatures prompted the wear debris adhesion and oxidation. After reaching a certain speed limit, a uniform third body appears to protect the material surface from high speed and high temperature. Results suggested that the BD-1 could be a good candidate braking material for high-speed railway applications. Full article

The brake system of Melbourne’s High-Capacity Metro Train (HCMT) suffers from consistently extended braking distances after repeating a set of high-speed tests and the commission process. The degradation of brake system performance affects the safety of rolling stock and its conformance to the design standard. In this paper, the root cause leading to the degraded brake performance was analyzed. The brake discs and brake pads of the affected train and another train with normal working conditions were removed and a series of examinations was to determine the reason for the change of friction coefficient between friction surfaces. The results revealed that brake disc samples from the affected TS02 trainset suffered from changed transfer film and surface morphology after multiple consecutive high-speed braking applications. The factors that may affect the brake system performance were analyzed in the laboratory. It was found the brake disc surface had a lower hardness level, coefficient of friction, and smaller contacting area with the brake pad when compared to the brake disc and pad samples from another trainset. These factors harmed the performance of the braking system, and the decrease in the braking effort led to a longer braking distance than expected and failed braking tests. Full article