Track Surface Research Articles

Process Parameter Optimization for Laser Powder Bed Fusion of Fe-Si Alloy Considering Surface Morphology and Track Width of Single Scan Track.

A laser power bed fusion (L-PBF) manufacturing process was optimized by analyzing the surface morphology and track width w of single scan tracks (SSTs) on Fe-3.4wt.%Si. An SST was evaluated under process conditions of laser power P, scan speed V, and energy density E = P/V. The SST surface shape was mainly affected by E; desirable thin and regular tracks were obtained at E = 0.3 and 0.4 J/mm. An L-PBF process window was proposed considering the optimal w of SST, and the appropriate range of E for the alloy was identified to be 0.24 J/mm to 0.49 J/mm. w showed a strong relationship with E and V, and an analytic model was suggested. To verify the process window derived from the appropriate w of SST, cubic samples were manufactured with the estimated optimal process conditions. Most samples produced had a high density with a porosity of <1%, and the process window derived from SST w data had high reliability. This study presents a comprehensive approach to enhancing additive manufacturing for Fe-3.4Si alloy, offering valuable insights for achieving high-quality samples without the need for time-intensive procedures.

Studies on fabrication of protruded multi-shaped micro-feature array on AA 6063 by laser micromachining

Miniaturization of parts of devices is the driving force for fabrication of micro-features. In this study fabrication of protruded multi-shaped micro-feature array on AA 6063 is attempted by laser micromachining. For fabricating the protruded microfeatures, the process parameters such as laser power, scanning speed and frequency of the laser beam have been optimized by considering track depth, width, and surface roughness as the output parameters. Three different cross sections in the tracks such as pileup section, W-section, and Gaussian groove section are observed. It is found that shape of the tracks vary with the scanning speed for the same power and frequency of the laser beam. The tracks of pileup section, W-section, and Gaussian groove section were produced for a laser scanning speed of 100 mm/s, 200mm/s, and 300 mm/s, respectively. Further, a laser-thermal ablative model is developed for predicting the depth of the single track and simulated using COMSOL® Multiphysics. The predicted track depths obtained from the simulations have good agreement with experimental results. In order to produce the protruded microfeatures of different shapes, multiple track analysis is done by fabricating the single tracks adjacent to one another by overlapping them, and the overlapping distance is optimized. The protruded microfeatures are then fabricated by removing the surrounding material for different scanning strategies and it is found that the contour strategy produced the features with minimal form error. Finally, it is demonstrated that an array of protruded micro-features of polygon (square, hexagon), and circular cross sections can be fabricated using the optimized process parameters for various applications.

Representativity of ISO test track surface based on controlled pass-by measurements

Within the Polish-Norwegian research project ELANORE, a limited Round Robin Test has been performed on four ISO tracks in Northern Europe. The basic objective of the project is to improve the EU directive on labelling of tyres for noise and rolling resistance. This directive is based on the measurement procedures proscribed in the UNECE Reg.117. Measurements on 3 ISO tracks were performed in 2021 and presented at InterNoise 2022. This paper adds results from tests conducted on a fourth ISO track as well as on trafficked roads with different conventional pavements: 2 in Norway (MA11 and SMA16) and 3 in Poland (SMA8, SMA11 and EACC). On all ISO test tracks and road test sites the same car, test tyres and test equipment as well as the same personnel were used to minimize the measurement uncertainties. Measurements were done using the controlled pass-by (CPB) method for vehicle test speeds between 40 and 90 km/h, with 2 test conditions: according to Reg.117 and with so-called "light test conditions". The main conclusion is that the noise ranking of the tyres on both, the ISO tracks and conventional pavements do not correspond to the ranking based on the label values given by tyre manufacturers.

Single-track investigation of additively manufactured mold steel with larger layer thickness processing: Track morphology, melt pool characteristics and defects

Large layer thickness is essential to increase building rate, but excessive layer thickness easily lead to defects which negatively affect component quality. The evolution of track morphology, melt pool characteristics and defects of additively manufactured mold steel by using various larger layer thickness (60 and 90 μm) while also varying the laser energy density was investigated systematically. Results indicated that the morphologies of single tracks shifted sequentially from discontinuousness to continuous irregularity and continuous regularity with the increasing line energy density at 60 μm layer thickness. The width and depth of melt pool increased substantially with the line energy density increased from 0.4 to 1.3 J/mm, while the height of melt pool was nearly constant. Correspondently, transition of the melt pool based on the depth-to-width ratio from balling to conduction and keyhole modes was observed. When the layer thickness increased from 60 to 90 μm, the average build percentage of the single tracks decreased by 43 % with increasing line energy density from 0.26 to 0.51 J/mm, and more spatters around the surface of tracks were found at 0.8 J/mm. Interestingly, the average width of the melt pool decreased by 37 μm, while the height of melt pool increased by 45 μm. More small spherical gas pores (5–15 μm) occurred in bottom of keyhole due to trapped vapor at high energy density. The decrease in melt width with increased layer thickness is most likely due to the weakened Marangoni convection. Finally, formation mechanism of lack-of-fusion defects and gas pores with larger layer thickness processing were analyzed based on melt pool characteristics, such as spheroidization, keyhole and spatters.

Implementation and analysis of viscoelastic damping in a 2D + 1D model of railway track vibrations

One of the most important technological challenges in the railway context nowadays is reducing the noise produced by the interaction between the train wheels and the track surface, that is the rolling noise. Introducing viscoelastic damping in the railway structure is one method to mitigate this rolling noise. In the paper, we investigate the impact of damping in the vibrational response of railway tracks using different viscoelastic models and parameters available in the literature. For this purpose, the main focus here is on developing an advanced numerical model in which viscoelastic models representing the rail foundation and/or pad are implemented in the framework of the Semi-Analytical Finite Element (SAFE) method. Linear or nonlinear viscoelastic models are considered, compared and effectively implemented for accelerance computation. The obtained numerical strategy leads to affordable and accurate predictions on dynamic features of the railway structure compared to classical methods.

Anodik Polarizasyon ve Kayma Aşınmasının Gemi İnşa Alüminyum Alaşımı 5083'ün Çukurcuk Korozyonu Davranışına Etkisi

This study aimed to characterize the pitting corrosion and simultaneous wear-corrosion (tribocorrosion) mechanisms of shipbuilding aluminum alloy 5083 under sliding wear and different anodic polarization conditions in simulated seawater. A tribocorrosion experimental setup was provided for the study under a 3 N load and different anodic potentials in a 3.5% NaCl solution. In the study, many grooves, parallel scratches and transverse cracks were determined on the wear track surface due to the low hardness of the test material. Chloride ions played a decisive role in the corrosion and tribocorrosion behavior of AA 5083. The dissolution of AA5083 increased from open circuit potential to higher anodic potentials. A half-cube mechanism, similar to the pitting corrosion of pure aluminum, and an intergranular pitting corrosion mechanism were observed under high anodic potentials.

Estimating the Ballast bed shape using Camcorder video

AbstractTo properly maintain and manage track surfaces, the amount of collapsed settlement of a ballast bed must be determined. However, high maintenance costs make it difficult for railway operators to fully maintain and manage track surfaces. Therefore, we propose a method of estimating the shape of the ballast bed using Dense Inverse Search (DIS) optical flow in images captured using a camcorder, which is inexpensive. This paper describes the outline of the method, an evaluation of its accuracy through simulation and model experiments, and the results of applying the method to actual images captured.

Development of Multifunctional Detection Robot for Roller Coaster Track.

Recent advances in roller coasters accelerate the creation of complex tracks to provide stimulation and excitement for humans. As the main load-bearing component, tracks are prone to damage such as loose connecting bolts, paint peeling, corroded sleeper welds, corroded butt welds, reduced track wall thickness and surface cracks under complex environments and long-term alternating loads. However, inspection of the roller coaster tracks, especially the high-altitude rolling tracks, is a crucial problem that traditional manual detection methods have difficulty solving. In addition, traditional inspection is labor-intensive, time-consuming, and provides only discrete information. Here, a concept of the multifunctional detection robot with a mechanical structure, electrical control system, camera, electromagnetic ultrasonic probes and an array of eddy current probes for detecting large roller coaster tracks is reported. By optimizing the design layout, integrating multiple systems and completing machine testing, the multifunctional roller coaster track detection robot exhibits outstanding performance in track appearance, thickness and crack detection. This study provides great potential for intelligent detection in amusement equipment, railcar, train and so on.

The Dynamic Train–Track Interaction on a Bridge and in a Tunnel Compared with the Simultaneous Vehicle, Track and Ground Vibration Measurements on a Surface Line

The vehicle–track interaction generates forces and consequently vibrations in the environment. The interaction has been analysed by the simultaneous measurements of vehicle, track and ground vibrations during test runs with varied train speeds. The special effects of the passage over a bridge and through a tunnel are studied and compared with the measurements on a conventional ballasted surface line. The maximum amplitudes, narrow band and one-third octave band spectra are presented for the axle-box accelerations and for the track, bridge and ground vibrations. The different frequencies and frequency bands are related to wheel out-of-roundness, track alignment errors, the sleeper passage and the wheelset–track resonance. An axle impulse component has been observed at the track, at the near-field soil and as a scattered version in the far field. Specific results can be found for the bridge track, where clearly speed-dependent bridge resonances occur due to the axle sequence of the train, and for the tunnel track where soft rail pads are responsible for a strong amplification around the wheelset–track resonance. On the other hand, the axle impulses are strongly reduced by the tunnel track, and the scattered axle impulse component is not as relevant as for the surface track. As a consequence, a strong mid-frequency amplitude reduction of the tunnel compared to the surface line has been measured for low and high train speeds by the Federal Institute of Material Research and Testing (BAM) and by other institutes.

The preliminary study of the forecasting model between surface texture and various material parameters for the ISO 10844 test track

Pavement surface texture is an essential factor in influencing the sound emission of vehicles, and reducing noise pollution would be a big issue for all humans. According to the Economic Commission for Europe (ECE) R-117 requirement, all the vehicle tires vending in Europe should pass noise accreditation after September 2009, and the pavement surface of the test track should follow ISO 10844. The Mean Profile Depth (MPD) is adopted to be the texture parameter of the test track surface in ISO 10844. the MPD of the Test track should be controlled at specific intervals, and the material design should be a big challenge of pavement Engineering. This study aims to establish an MPD prediction function with material properties for pavement Engineers. In material, there were two fine aggregates, three gradation curves, three air voids of the specimen, and 18 mixture designs adopted in this study. There were three specimens in each mixture design; the total specimen number was 54 for MPD measurement. Fifty-four laboratory test specimens were compacted using a Superpave gyratory compactor (SGC). A High-Definition Pavement Texture Machine (HDPTM) measured the specimen surface MPD. The parameters in this study included fineness module (FM), fine aggregate angularity (FAA), air void (AV) of the specimen, and Gyration number (G) of SGC. Gene Expression Programming (GEP) was adopted to build a prediction model between MPD and various parameters. Based on the results of this study, the best MPD forecasting model using FAA, FM, and AV, the R2 of is 0.74, meaning the best MPD forecasting model could be a very nice tool to help pavement engineers to do MPD quality control on the test track for ISO 10844. In addition, GEP was an excellent method to discover the nonlinear relationship between MPD and various parameters of asphalt concrete, and it was worthy of further study.

A novel method for optimizing in-car rolling noise levels within a railway tunnel environment

In-car noise levels within trains rolling on surface track are usually controlled by noise and vibration which is generated at the wheel–rail interface and then transmitted through the chassis and floor of the train cabin. In a railway tunnel environment, higher noises levels result from the build up of reverberant noise, and if left untreated this increased noise can affect passenger comfort and make it harder to listen or converse. In extreme cases, it can lead to adverse health effects: travellers may complain and avoid using the rail service as a result. Accordingly, the acoustic design of railway tunnel environments generally includes consideration of various treatments to reduce noise ingress into vehicle interiors, particularly given treatments to the vehicles themselves may not be cost effective. Modeling of in-car noise levels within tunnels has traditionally used the Sabine equation as part of the design process. Because the Sabine equation was never intended for this application given the geometry and frequencies involved, an improved method which recognized the near field effects was developed in order to provide confidence in the acoustic design. In this presentation, this novel method for modeling in-car rolling noise levels and optimizing sound absorptive treatments within a tunnel is discussed. Modeling results and measurements from a recent major rail project are used to demonstrate the effectiveness and improvements in outcomes from traditional approaches.

Detecting surface discharge faults in switchgear by using hybrid model

&lt;span&gt;Switchgear plays a crucial role in power systems, providing protection and control over electrical equipment. However, tracking (surface discharge) can lead to insulation degradation and switchgear failure, necessitating reliable and effective identification of tracking defects. In this paper, we propose a hybrid one-dimension convolutional neural network long short-term memory networks (1D-CNN-LSTM) model as a solution to this problem. Data from both time domain analysis (TDA) and frequency domain analysis (FDA) are utilized for model evaluation. The model achieved error-free accuracy of 100% in both TDA and FDA during the training, validation, and testing phases. The model's performance is further assessed using performance measures and the visualization of accuracy and loss curves. The results show that the hybrid 1D-CNN-LSTM model works well to accurately find and classify surface discharge tracking defects in switchgear. The model offers precise and dependable fault identification, which has the potential to significantly enhance switchgear functionality. By enabling proactive maintenance and timely intervention, the proposed model contributes to the overall reliability and performance of switchgear in power systems. The findings of this research provide valuable insights for the design and implementation of advanced fault detection systems in switchgear applications.&lt;/span&gt;

Validation of a railway rolling noise model on a system with slab track and resilient wheels

This study investigates rolling noise emissions using an analytical model of the Seattle Sound Transit Light Rail system developed using Train Noise Expert (TNE) software. Measurements of track frequency response, decay rate, rail and wheel roughness were used to determine model input parameters. Wheel modal test results were used to characterize the wheels. Wayside noise and track vibration measurements during revenue service train passbys were used to experimentally validate the model. The average difference between measured and predicted overall passby LAeq noise at a position immediately adjacent to the track was 0.1 dBA (average from four scenarios, i.e. two surface track sites with two train types). Inspection of the predicted versus measured noise spectra indicates the model does not exactly match the measured spectrum in every frequency band, however the correlation with overall spectrum shape is good in the frequency bands that contribute most to the overall A-weighted level. It is concluded that the model provides an accurate representation of the most relevant physical rolling noise factors and is reliable with resilient wheels and light rail vehicles on ballast and slab track.

Acoustic labelling of tires, road vehicles and road pavements: A vision for substantially improved procedures

The EU requires vehicle tires to be tested for noise emission and labelled. Some other countries also have similar procedures. Preparations for labelling of acoustical properties of road pavements is also ongoing in EU. Road vehicles and their tires must be tested and meet noise limits worldwide. However, all cases involve problems with measurement methods and conditions, which create uncertainties higher than desirable to make fair decisions on which product to select. For tires and road vehicles the major obstacle is the test track surface, which cannot be sufficiently well defined and reproducible. Also, far from all products (tires) are measured, so commonly only the noisiest products are correctly labelled. Although attempts are made to go indoors to do the measurements, they are still for the foreseeable future going to be made outdoors, with all the influence of weather and seasons that this causes. The author has worked most of his long career with such issues and in this paper, the author outlines his vision of how most of the problems (uncertainties) can be reduced to acceptable levels, mainly by making measurements indoors, with reproducible and representative conditions for both the labelling and the actual noise emission in traffic.

Tribological behavior of MoS2/a-C:Si composite films in high-temperature air and vacuum environments

MoS2/a-C:Si composite films doped with different contents of carbon (C) and silicon (Si) were deposited using a hybrid deposition system consisting of a superimposed high-power impulse magnetron sputtering (HiPIMS)-direct current magnetron sputtering (DCMS) and a mid-frequency magnetron sputtering (MFMS). The content of C and Si elements in the films was controlled by changing the direct current (DC) of the graphite-silicon (C-Si) mosaic target. The effects of C and Si doping on the microstructure and mechanical properties of the films were investigated. In addition, the tribological behavior of the films in high-temperature air (up to 350 °C) and vacuum environments was evaluated in detail. The results suggested that MoS2/a-C:Si composite films exhibited excellent tribological properties in both high-temperature air and vacuum environments. MoS2/a-C:Si composite films doped with C and Si elements exhibited low coefficient of friction (COF) and wear rate (WR) at elevated temperatures due to the improved thermal stability. In particular, MoS2/a-C:Si composite film with 40.37 at% C displayed a low COF of 0.051 and a low WR of 1.47 × 10 −6 mm3/(N·m) at 350 °C in air. Moreover, MoS2/a-C:Si composite film also exhibited excellent tribological properties under vacuum conditions due to the precipitation of C on the wear track surface. The COF of MoS2/a-C:Si composite film with 40.37 at% C under vacuum conditions was as low as 0.018, and the WR of the film was as low as 1.99 × 10 −7 mm3/(N·m).

Synthesis of Polymer-Grafted Carbon Dots Serving as Multifunctional Lubricant Additives with Excellent Tribological Performance and Additional Rust Resistance Function for Steel/Steel Contact.

Poly(bis(2-ethylhexyl) phosphoric) methacrylic anhydride-grafted carbon dots (CD-g-PEPMA) have been controllably synthesized and used as multifunctional lubricant additives of poly(ethylene glycol) (PEG200). The polymers on the surfaces of CD-g-PEPMA not only endow them with particularly excellent dispersion stability but also enhance their adsorbability on the steel surface and embedded stability between the rubbing surfaces. Hence, CD-g-PEPMA as an additive showed outstanding rust resistance and tribological performance. Among CD-g-PEPMA-X (X represents the polymerization time), CD-g-PEPMA-2 (X = 2 h) exhibited the best tribological performance. At the optimum c of 2.0 wt %, CD-g-PEPMA-2 reduced the coefficient of friction and wear volume of PEG200 by 60.1 and 74.0%, respectively. The striking friction-reducing and antiwear functions of CD-g-PEPMA as additives can be attributed to the synergistic lubrication effect of carbon cores and polymers. The rolling, polishing, and mending effects of carbon cores combined with the favorable adsorbability and reactivity of polymers on steel surfaces synergistically induced the formation of boundary lubrication films on wear track surfaces. The films are composed of tribochemical reaction products such as Fe2(CO3)3, Fe3C, and FePO4 embedded with carbon cores, tremendously reducing the friction and wear of the friction pair. The research results can provide substantial theoretical guidance and data support for designing and developing high-efficiency polymer-CD integrative multifunctional nanoadditives toward PEG.

Evolutionary power spectral density study of the earthquake-induced dynamic irregularity based on short-time Fourier transform

The stiffness degradation of the track-bridge system under earthquake is the main reason for the deterioration of track dynamic smoothness. In order to investigate the dynamic smoothness performance of the track surface of the track-bridge system after earthquake. In this paper, a nonlinear time analysis of ballastless track-simply supported bridge system under transverse random earthquakes is carried out, and the degradation mode and degradation degree of each key component of the track-bridge system after transverse earthquakes are investigated. Based on the post-earthquake stiffness of each component, a train-track-bridge system considering earthquake-induced stiffness degradation is established. The sample library of earthquake-induced dynamic irregularity is constructed by additional deformation of rails, and the power spectral density of the earthquake-induced dynamic irregularity is studied. Based on the short-time Fourier transform irregularity inversion technique, the earthquake-induced dynamic irregularity characteristic curve based on the probability guarantee rate is proposed, and the effects of train operating speed and ground vibration intensity on the earthquake-induced dynamic irregularity characteristic curve are investigated. The research results show that: The transverse stiffness degradation of the bearings and piers of the track-bridge system is the most obvious during an earthquake, and the stiffness degradation degree of the middle piers is greater than that of the side piers. The stiffness degradation degree of the track-bridge system rises significantly with increasing PGA, while the variability of stiffness degradation of the middle and side piers drops. The most significant earthquake-induced dynamic irregularity sample is the track alignment irregularity. Low-frequency components dominate the evolutionary power spectral density corresponding to track dynamic irregularity, and the amplitude of the power spectral density reduces considerably with increasing spatial frequency. The vehicle speed has little effect on the earthquake-induced track dynamic irregularity. The irregularity amplitude grows significantly with increasing damage degree. The results indicated that the stiffness degradation damage degree of the track-bridge system under earthquake can be quantified by constructive earthquake-induced track dynamic irregularity.

Spatial trace and rare earth elemental compositions of surficial sediments on the high Mountains, Central Asia, and implications for desert sand and Asian dust

As one of the major mountain systems in Central Asia, the Tianshan Mountains provide vast amounts of sediment to adjacent areas. The elemental compositions of surficial sediments on the piedmont of the Tianshan Mountains were investigated to track surface processes. However, spatial comparisons of the elemental compositions of the sediments in the Tianshan Mountains and adjacent areas remain limited. To address this issue, this study investigated the trace element compositions (including rare earth elements (REEs)) of surficial sediments in a vast region ranging from the Pamirs, Tarim Basin, and Tianshan Mountains to the Junggar Basin. According to statistical analyses of the selected source tracers of trace element and REE ratios, this large region can be geochemically divided into two regions. One region comprises the Pamirs, Tarim Basin, and South and Central Tianshan Mountains (PTSC), where the sediments are characterized by contrary source tracer ratios compared with the other region comprising the Yili Basin, North Tianshan, and Junggar Basin (YNTJ). We suggest that the source bedrock is the primary factor controlling the trace element and REE compositions in these two regions. The trace element and REE compositions in the PTSC and YNTJ regions represent signatures of the two endmembers of Asian dust. The trace compositions of loess deposits on the Chinese Loess Plateau (CLP) and Asian dust archived in the North Pacific Ocean (NPO) mostly resemble those of sediments in the PTSC region, suggesting that Asian dust is mainly derived from sediments eroded from the North Tibetan Plateau. Our study enriches our understanding of the source materials of Asian dust archived in the CLP and NPO.

Developing bottom drifters to better understand the stranding locations of cold-stunned sea turtles in Cape Cod Bay, Massachusetts.

Every fall, juvenile sea turtles in the Northwest Atlantic Ocean are threatened by rapidly declining water temperatures. When sea turtles become hypothermic, or cold-stunned, they lose mobility-either at the surface, subsurface, or the bottom of the water column-and eventually strand at the shoreline where rescue teams associated with the Sea Turtle Stranding and Salvage Network may search for them. Understanding the effects of ocean currents on the potential stranding locations of cold-stunned sea turtles is essential to better understand stranding hotspots and increase the probability of successful discovery and recovery of turtles before they die in the cold temperatures. Traditional oceanographic drifters-instruments used to track currents-have been used to examine relationships between current and stranding locations in Cape Cod Bay, but these drifters are not representative of sea turtle morphology and do not assess how bottom currents affect stranding locations. To address these knowledge gaps, we designed new drifters that represent the shape and dimensions of sea turtles-one that can float at the surface and one that sinks to the bottom-to track both surface and bottom currents in Cape Cod Bay. We found a marked difference between the trajectories of our new drifter models and those that were previously used for similar research. These findings bring us one step closer to identifying the transport pathways for cold-stunned sea turtles and optimizing cold-stunned sea turtle search and rescue efforts in Cape Cod.

Numerical Simulations and Wind Tunnel Experiments to Optimize the Parameters of the Second Sand Fence and Prevent Sand Accumulation on the Subgrade of a Desert Railway

Wind-blown sand significantly affects the construction and safe operation of railways in desert regions. The performance of a wind-blown-sand prevention system with different structural parameters and sand accumulation around the railway subgrade was analyzed in this study. The optimum porosity and opening type of a second sand fence were assessed via wind tunnel experiments and numerical simulations. The results showed that the subgrade intercepted some sand and reduced sand accumulation on the track surface, and the interception rate was 29.70%. The wind-blown-sand prevention efficiency of the subgrade was 88.55%. Moreover, the lower the porosity of the second sand fence, the lower the sand velocity on the windward side and the higher the sand accumulation. The porosities of the first and second sand fences should be 30% and 20%, respectively, to maximize the sand accumulation between the fences. When the second sand fence had horizontal openings, most of the sand accumulated near the surface (within 20 cm) on the leeward side and on the straw checkerboard barrier, and the maximum wind-blown-sand prevention efficiency was 97.16%. When the second sand fence had vertical openings, the efficiency was 93.60%, and the sand accumulation on the leeward side and the straw checkerboard barrier was reduced. As the fence height increased (above 20 cm), the sand prevention efficiency of both approaches increased. The research results can provide guidance for the formulation and optimization of sand prevention measures for railways and highways in deserts.