Increase Of Axle Load Research Articles

An innovative rheological approach for predicting the behaviour of critical zones in a railway track

The poor performance of critical zones along a railway line has long been a subject of concern for rail infrastructure managers. The rapid deterioration of track geometry in these zones is primarily ascribed to limited understanding of the underlying mechanism and scarcity of adequate tools to assess the severity of the potential issue. Therefore, a comprehensive evaluation of their behaviour is paramount to improve the design and ensure adequate service quality. With this objective, a novel methodology is introduced, which can predict the differential plastic deformations at the critical zones and assess the suitability of different countermeasures in improving the track performance. The proposed technique employs a three-dimensional geotechnical rheological track model that considers varied support conditions of the critical zone. The approach is successfully validated with published field data and predictions from finite element analysis. This methodology is then applied to a bridge-open track transition zone, where it is observed that an increase in axle load exacerbates the track geometry degradation problem. The results show that the performance of critical zones with weak subgrade can be improved by increasing the granular layer thickness. Interpretation of the predicted differential settlement for different countermeasures exemplifies the practical significance of the proposed methodology.

Influence of Axle Load on the Wear of Railway Wheel Material

This study investigated the influence of axle load on the wear rate of railway wheel material. Excessive wear of wheel/rail materials and reduced service life of the wheel/rail system might be caused by the increase in axle load and traffic volume. Two kinds of rail and wheel steels have been studied against different axle load steps, simulating them for wear performance analysis using multibody simulation software (SIMPACK) and MATLAB programming. The simulation model results are validated against the vehicle’s specifications and wear depth measured on Ethiopia—Addis Ababa Light Rail Transit (LRT), and experimental results from the literature. The result shows that the wear rate increases proportionally with the increasing of applied load and that the proportionality coefficient is 0.1393, which has a very good agreement with the experimental results from the works of literature. Likewise, the estimated total tread wear amount after a mileage of 52,000 km is 2% larger than the measured one in LRT, which is indeed an excellent result taking into account the inaccuracy of the wheel diameter gauge used to measure the wheel transversal profile. In normalized UIC 50 kg/m rail and S1002 wheel profile, the wear rate increases linearly from 5110.02, 9997.87, and 18990.17 mm3/km on 11, 21, and 30 tones applied load, respectively. Apparently, on the hardened UIC 60 kg/m and S1002 wheel profiles, the wear rate has been improved by 14.5%, 10.8%, and 7.5% on 11, 21, and 30 tones applied load, respectively, in comparison to normalized rail/wheel match. Briefly, the wheel wear rate is highly influenced by the increasing applied load, referring proportionality coefficient of 0.1393.

Effect of normal load on the wear and rolling contact fatigue behaviour of AAR class B wheel against R350HT rail in a twin disc simulator

The normal load at the wheel-rail contact interface plays a significant role in wear and rolling contact fatigue (RCF) performance of both wheel and rail steels. In recent years, there has been an increase in axle loads due to increased demand for railway services. This study investigated the effect of normal load on the wear and RCF behaviour of the AAR class B wheel versus R350HT rail using a twin disc wear simulator. The mass loss, surface damage and depth of deformation were used to assess wear and RCF, respectively. From the mass loss results, wear maps were obtained to identify different wear regimes being mild, severe and catastrophic at different contact loads and slip ratios. Scanning electron microscopy was also used to assess the surface damage of wheel and rail steels in order to identify the wear regimes with surface cracking and delamination being observed at higher contact loads indicating severe and catastrophic wear. Furthermore, the RCF crack density was found to be higher on specimens evaluated at higher normal loads with more cracks evident and crack branching forming.

Study of rolling contact fatigue, rolling and sliding wear of class B wheel steels against R350HT and R260 rail steels under dry contact conditions using the twin disc setup

There is an increased demand for railway services, which has resulted in an increase in speeds and axle loads. The increase in axle loads and speeds have resulted in an increase in severity of wheel and rail wear. The aim of this work was to investigate wear and rolling contact fatigue (RCF) performance of class B wheels against R350HT and R260 rail under different slip ratio using a twin-disc setup. The results showed that severity of wear was heavily dependent on slip ratio. It was found that class B wheels’ wear rate was better against R260 rail than against R350HT rail. Three wear regimes were identified from plots of wear rate versus wear index (Tγ/A) being mild, severe and catastrophic.

Study on the adhesion behavior of wheel/rail under water conditions by using mixed lubrication model

PurposeThe purpose of this paper is to propose a wheel/rail mixed lubrication model to study the water lubrication behavior of wheel/rail contact interface.Design/methodology/approachThe numerical simulation method is applied in this paper. A deterministic mixed lubrication model considering surface roughness and transient state is established. The quasi-system numerical and finite difference method are used for numerical solution. The model is verified by comparing with the experimental data in the literature under the same conditions.FindingsUnder wet conditions, the change of train speed will change the lubrication state of the wheel/rail contact interface. With an increasing speed, the average film thickness and the film thickness ratio increase, while the adhesion coefficient, the contact load ratio and the contact area ratio decrease. When the creep ratio increases from 0% to 0.5%, the wheel/rail adhesion coefficient and subsurface stress increase sharply. With the increase of axle load, the average film thickness decreases and the adhesion coefficient increases.Practical implicationsThis paper aims to improve the mixed lubrication theory by analyzing the characteristics of wheel/rail friction and lubrication, so as to provide some guidance and theory for train driving behavior.Originality/valueUsing the deterministic model, the lubrication state of the wheel/rail contact interface affected by various external factors and the adhesion behavior of wheel/rail progressive process from boundary lubrication to mixed lubrication are studied.

Evolution of trackbed performance and ballast degradation due to passages of million train wheel axle loads

The increases in train speeds and wheel axle loads produce significantly higher dynamic responses and ballast breakage in ballasted tracks, which could cause reduced trackbed performance and the deterioration of the ballast particles under long-term train traffic loads. To evaluate trackbed performance under long-term moving train loads, a full-scale ballasted track experiment with eight sleepers was designed and tested on a validated physical model test platform (ZJU-iHSRT).Sleeper support stiffness is a qualitative index of the ballasted track in the evaluation of trackbed performance, which was studied based on the sleeper displacement measured by a laser displacement sensor during the test.Then, ballast breakage analysis was conducted to quantify the ballast degradation of ballast particles after every 400,000 passes of train wheel axle loads through the sieving test of particle size distribution.Vibration velocity sensors and “SmartRock” wireless sensors were installed at specific locations in the ballast layer to compare the ballast dynamic responses before and after the implementation of long-term train traffic loads. The test results showed that both the static and dynamic sleeper support stiffness increased tremendously with the densification of trackbed caused by long-term train loads; especially, heavy train loads increased the BBI by 60% and doubled the static sleeper support stiffness. The evolution of static sleeper support stiffness and ballast breakage showed a similar trend, which significantly intensified with the increase in train speed, then stabilized with the number of train wheel axle loads, and increased sharply again due to the increase in axle load. Ballast breakage and particle rearrangement made the small particles fill the ballast voids, which enhanced the densification of ballast particles, thereby reducing the trackbed elasticity.

Damage behavior of heavy-haul rail steels used from the mild conditions to harsh conditions

Systematic experimental investigations were conducted to study the damage behavior of rail steels with eutectoid and hypereutectoid microstructure under different axle load and curve radius conditions. The wear resistance and resulting failure mechanism, as well as subsurface crack development were evaluated by wheel/rail rolling contact test rig, which can realize a broad range of working conditions from mild condition to harsh condition. Results demonstrate that the wear resistance and rolling contact fatigue (RCF) damage depend on not only the working conditions employed, but also the microstructures. With the increase of axle load and reduction of curve radius, the wear rate increases for both rail steels. Damage mechanisms for the two rail materials are mainly surface fatigue cracks and delamination, which become much serious from the mild condition to harsh condition. The hypereutectoid rail possesses a better wear resistance than eutectoid rail in general. Wear regime map suggests that the hypereutectoid rail did not have a catastrophic wear region, but can be observed in eutectoid rail. The subsurface analysis shows that the working condition has a significant impact on surface crack development depending on specific microstructure types. The hypereutectoid rail is more suitable for harsh working conditions than eutectoid rail.

Dynamic constitutive model of U75VG rail flash-butt welded joint and its application in wheel-rail transient rolling contact simulation

Rail welded joint is one of weak links in high-speed railway, and its dynamic performance has important effects on the safety, stability, and comfort of the high-speed train. In this work, the dynamic mechanical responses at different regions of U75VG rail flash-butt welded joint were investigated. The results show that the base metal (BM), welding zone (WZ), and heat-affected zone (HAZ) of U75VG rail flash-butt welded joint has an obvious strain rate effect, i.e., the material strength increases with increasing the loading strain rate. The strength of WZ is similar to that of BM, but its toughness is much lower than that of BM. The toughness of HAZ is the same as that of WZ, but its strength is much lower than that of BM and WZ. Based on the experimental results, an improved dynamic constitutive model was established to reasonably simulate the stress–strain curves of different regions from quasi-static loading to dynamic loading. Finite element (FE) analysis of transient rolling contact between rail welded joint and wheel under different conditions was performed. Compared with the results from quasi-static wheel-rail contact simulation, the equivalent plastic strain at each region of rail welded joint increases significantly and presents non-uniform distribution after considering the dynamic effect. When the wheel contacts the junction between different regions, the impact will cause a significant stress concentration at the rail welded joints. The maximum wheel-rail load by the implicit dynamic analysis is about 4 ∼ 12 times that obtained by the quasi-static analysis. Moreover, the maximum contact pressure, equivalent stress and equivalent plastic strain of each area of rail welded joints gradually increase with the increase in axle load and driving speed.

Dynamic Response Characteristics of the Electric Domain Structure of Ferroelectric Materials to the Surrounding Rock Structure of a Heavy‐Duty Railway with a Small‐Clearance Crossing Tunnel

At present, the world‐wide heavy‐haul transportation technology of cargo trains has developed rapidly. Heavy‐haul railway transportation has received extensive attention due to its large capacity, high efficiency, and low transportation costs. In order to understand the role that ferroelectric materials can play in the dynamic response of a heavy‐duty railway surrounding rock structures in crosstunnels, this article introduces the domain structure of ferroelectric materials, derives the calculation method of the dynamic response of the surrounding rock structure, simulates the dynamic response characteristics through the corresponding formula, and analyzes the changes of the heavy‐duty railway in the presence and absence of water. The situation was analyzed. The research results found that the increase of axle load will increase the bending moment of the invert structure. When the axle load is 30 t, the V‐class surrounding rock is the most unfavorable working condition and the bending moment value of the invert structure is the largest at this time. When the added value of contact pressure is generally around 6.5 kPa, the railway as a whole can maintain a stable state.

Effect of dynamic load and cooling path on the frost characteristics of saturated lean clay

With the traffic load increase in heavy-haul railways, the subgrade's frost heave damage should be emphasized in colder seasons for operational safety. The effects of dynamic vehicle load (mean value and frequency), step cooling path, and dry density on filler's frost characteristics are not explored in existing heavy-haul lines. This study performed L9(43) orthogonal tests for saturated lean clay filler. The test results were analyzed using the analysis of variance method and the grey incidence (GI) model. The external water supply caused a shallower frozen depth, more segregated ice, and a frost heave ratio exceeding 4.0% under a dynamic load. The dry density, associated with the migrating water's permeability, had the highest significance on the open system's frost heave. As the phase change of water depends on the negative temperature, the step cooling path had the highest impact on the frost heave ratio and frozen depth in the closed system. The significance of dynamic load on the frost heave ratio was slight, so an increase in axle load and operating speed had little impact on the lean clay's frost heave characteristics. Compared with other factors, the water supply conditions had the most significant impact on the test results. This study clarifies the significance of the four factors on the filler's frost characteristics in heavy-haul railways, which serves as an essential guide to frost damage management.

Railway embankment behaviour due to increased axle loads - A numerical study

Due to an increase in axle loads, the development of excess pore water pressure and settlement in a railway track foundation of fine-grained subgrade soil can be observed. A thorough understanding of the mechanism of development of excess pore water pressure is essential for understanding the development of settlements and the design of potential ground improvement. In this paper, a three dimensional numerical study is presented, which investigates the effects of an increase in axle loads of trains on both excess pore water pressure and settlement. Special attention is given to a soft soil layer beneath the embankment and the influence of ground improvement (deep soil mixing columns). As a result, an increase in axle loads leads to a considerable increase in both excess pore pressures and settlement in the subgrade layer. This increase is more significant in the case of heavy axle load (32.5 tons) than that of the light axle load (16 tons). In addition, cyclic loading can lead to a considerable increase in both vertical displacements and excess pore water pressure. The use of deep soil mixing columns reduces excess pore water pressures and settlements significantly.

A Review on Microstructural Features and Mechanical Properties of Wheels/Rails Cladded by Laser Cladding.

The service life of rails would be remarkably reduced owing to the increase of axle load, which can induce the occurrence of damages such as cracks, collapse, fat edges, etc. Laser cladding, which can enhance the mechanical properties of the rail by creating a coating, has received great attention in the area of the rails due to the attractive advantages such as low input heat, small heat-affected zone, and small deformation. In this paper, recent developments in the microstructural characteristics and mechanical properties of a cladded layer on the rail are reviewed. The method of process optimization for enhancing the properties of a cladded layer are discussed. Finally, the trend of future development is forecasted.

Theoretical analysis and experimental research on multi-layer elastic damping track structure

The increase of axle load and train speed would cause intense wheelrail interactions, and lead to potential vibration related problems in train operation. For the low-frequency vibration reduction of a track system, a multi-layer track structure was proposed and analyzed theoretically and experimentally. Firstly, the analytical solution was derived theoretically, and followed by a parametric analysis to verify the vibration reduction performance. Then, a finite element simulation is carried out to highlight the influence of the tuned slab damper. Finally, the vibration and noise tests are performed to verify the results of the analytical solution and finite element simulation. As the finite element simulation indicates, after installation of the tuned slab damper, the peak reaction force of the foundation can be reduced by 60%, and the peak value of the vertical vibration acceleration would decrease by 50%. The vibration test results show that the insertion losses for the total vibration levels are 13.3 dB in the vertical direction and 21.7 dB in the transverse direction. The noise test results show that the data of each measurement point is smoother and smaller, and the noise in the generating position and propagation path can be reduced by 1.9 dB–5.5 dB.

Influence of Tire Crumb Rubber on Properties of Asphalt Binders

For many years, the asphalt binder has been used as the elemental material for pavement engineering. The increase in axle loads, heavy traffic, severe climate conditions and construction failures has led many researchers to seek some methods to enhance the bitumen properties. There is a wide range of applications of modifiers for bitumen in road construction. Although various kinds of modifiers have been used widely in reinforcing asphalt concrete, crumb rubber has attracted the most attention due to its high and desirable characteristics. It is realized that the well-distributed modifier can create a strong network in the internal structure of the composite, resulting in asphalt mastic that is more coherent. In the present paper, a laboratory investigation of the physical and rheological properties of various grades of asphalt binder (60-70 penetration grade, 80-100 penetration grade and PG-76 grade) modified with tire crumb rubber. The results showed improvement in physical properties of the modified asphalt binders in terms of decreasing in penetration, increasing in softening point and viscosity values. The modified bitumens exhibited enhanced rheological performance and could raise the grade of bitumen relying on the base asphalt type.

Experimental study to examine the role of under sleeper pads for improved performance of ballast under cyclic loading

The degradation and deformation of ballast critically affect the track geometry, safety, and passenger comfort. The increase in axle loads and train speed increases the stress applied on the ballast and exacerbates the rate of ballast degradation. This situation is more critical when tracks are built on stiff subgrades (e.g. bridges, tunnels and crossings), hence the use of energy absorbing (damping) layers in track substructure is a countermeasure to minimize track damage. In this study, a series of large-scale laboratory tests using the track process simulation testing apparatus (TPSA) is carried out to assess the performance of under sleeper pads (USP) to reduce ballast degradation and to decrease permanent deformation. When placed beneath the sleeper, the energy absorbing nature of USP reduces the energy transferred to the ballast and other substructure components. Subsequently, the ballast layer experiences less deformation and degradation. Innovative tactile surface sensors (matrix-based) are used to measure the pressure and contact area between sleeper and ballast. The measured data show that an increase in contact area between sleeper and ballast decreases the stress applied on ballast, and thus a reduction in ballast breakage and corresponding reduced ballast deformation can be achieved. Furthermore, the influence of the USP stiffness is examined and the measured data offer an insightful understanding of the role of USP for given track and loading conditions in terms of energy dissipation and reduced ballast deformation.

Random distribution characteristics of peak dynamic stress on the subgrade surface of heavy-haul railways considering track irregularities

The dynamic response of the subgrade surface under moving train loads provides information for subgrade settlement prediction, condition evaluation and so forth. In this paper, a 3D dynamic finite element (FE) model that considers the interactions among the wagon, track and subgrade was built. Then, the irregular vertical track spectrum of the three major lines in China was applied to simulate track irregularity. Through numerical calculation, the influence of vertical track irregularity on the dynamic stress of subgrade surface was investigated. The distributions of peak dynamic stresses at three subgrade surface locations (under each of the two rails and at the track center) along the track under the passage of trains with various axle loads were statistically acquired. The normal distributions of the peak dynamic stresses on the subgrade surface were verified. The maximum peak dynamic stresses were forecasted. The results indicated that the dynamic stresses on the subgrade surface were asymmetric along the center of subgrade surface due to the random distribution of track irregularities, and the peak dynamic stresses were found to follow a normal distribution. With the increase of axle load, the dispersion of peak dynamic stresses increased gradually, and the distribution curve of peak dynamic stresses gradually became steeper. The computed peak dynamic stresses aligned well with the field test data, indicating that the 3D dynamic FE model and statistical analysis method were reasonable. The research results will provide a basis for the reliability analysis of the dynamic deformation and accumulated settlement of subgrade surface.

Influence of the axial loads of rolling stock on the contact-fatigue life of rails

Analysis of operational data for defective and highly defective rails showed that up to 25 % is the contact-fatigue defects. In connection with the development of heavy haul traffic on the Russian railways, it is relevant to determine the influence of cars with increased axial loads of 25 and 27 tf on the contact fatigue life of rails. The solution of this problem is set forth in this article. The Brown-Miller model of multi-axial fatigue was used in the calculation. This model is integrated into the Fatigue software system, which is tied to the Marc calculation system through Pat-ran. Since under operating conditions the wheel moves (rolls) along the rail on meandering trajectory, in computer modeling weight coefficients were taken into account that characterize the percentage of wheels in the cross-sectional areas of the rail. Calculations of contact fatigue life took into account the variability of vertical loads from the impact on the track of trains formed from innovative open cars with axial loads of 23.5, 25 and 27 tf under operating conditions, loaded with real loading blocks. According to the analysis of calculated data with an increase in axial loads from 23.5 to 25 tf, it is necessary to expect a decrease in the service life of rails in contact fatigue resistance by 19 %, with a further increase in axle loads of up to 27 tf per 32 %. Considering that the share of freight cars with axial loads of 25 tf does not exceed 15...20 %, then on the routes of its use the service life of rails should be expected to decrease by 3...4 %. The method proposed by the authors for predicting the contact fatigue life of rails with increasing axial loads is advisable to improve in part of the experimental determination of the fatigue and strength characteristics of rail steel from the degree of hardening of the rolling surface, its probabilistic properties and the use of the integral distribution law for vertical forces, taking into account the structure of the freight traffic passing through the section. The work was carried out according to the RFBR project 17-20 01088.

Wheel life prediction model – an alternative to the FASTSIM algorithm for RCF

ABSTRACTIn this article, a wheel life prediction model considering wear and rolling contact fatigue (RCF) is developed and applied to a heavy-haul locomotive. For wear calculations, a methodology based on Archard's wear calculation theory is used. The simulated wear depth is compared with profile measurements within 100,000 km. For RCF, a shakedown-based theory is applied locally, using the FaStrip algorithm to estimate the tangential stresses instead of FASTSIM. The differences between the two algorithms on damage prediction models are studied. The running distance between the two reprofiling due to RCF is estimated based on a Wöhler-like relationship developed from laboratory test results from the literature and the Palmgren-Miner rule. The simulated crack locations and their angles are compared with a five-year field study. Calculations to study the effects of electro-dynamic braking, track gauge, harder wheel material and the increase of axle load on the wheel life are also carried out.

The Service Life of Ballastless Track

Before the widespread use of high-speed rail ballastless track needs to be tested in real conditions at high speed and small axial load. Experimental railway track of “VNIIZhT” makes it possible to carry out tests at high axial load, low speed but that does not fully meet the real fields of application of ballastless track. To resolve this contradiction it proposed to apply the methodology of forecasting resource of ballastless track under real operating conditions basing on the results of tests on an experimental ring using mathematical modeling.The proposed algorithm and methodology allow applying results of observation of degradation of tested ballastless track design on the Test Loop (Scherbinka railway station) to the network section where laying of any ballastless track design for mixed traffic is planned.In the longer term this methodology will give opportunity to take into account changes of operational factors on a section, including impact of increase of axle load or train speed on durability of track design.

Effects of rail materials and axle loads on the wear behavior of wheel/rail steels

Four kinds of rail steels were tested to investigate the wear behaviors of wheel–rail materials under three kinds of axle loads. Results indicate that the increase in axle load not only significantly enlarges the wear loss but also enlarges the depth and the length of the fatigue cracks. However, with the decreases in the hardness ratios, some ripples are exhibited on the surface, and the wear surfaces become much rougher; the subsurface analyses deliver the presence of extremely rough surface, and the deformation depths are irregular. The relationship between the total wear loss of the wheel/rail system and the hardness ratio indicates that the hardness ratio of wheel/rail steels has slight impact on the total wear loss at a low axle load; however, the decrease in the hardness ratio enlarges the total wear loss significantly at a high axle load. In summary, a quenched rail should be chosen for the heavy-haul railway, and the hardness of the wheel steel should be raised to a degree close to the rail. However, a hot rolled rail is much suitable for the high-speed railway, and the wheel hardness should be smaller than the rail.