High-speed Train Body Research Articles

A three-stage framework for accurate detection of high-speed train body paint film defects

Detecting paint film defects on high-speed train (HST) body is a crucial step towards zero-defect manufacturing (ZDM). The effectiveness of defect detection in industrial environments, however, is significantly impacted by factors such as high reflection noise, weak defect features, small defect size, and various defect scales, resulting in unsatisfactory detection accuracy. To address these challenges, this paper proposes a technical framework for the accurate detection of paint film defects on HST body, encompassing three stages. A reflection detection removal method that takes into account the reflection transition region as well as the preservation of defect features is at first used to reduce reflection noise interference. Then a lightness-weighted adaptive image enhancement algorithm based on the fractional order differentiation is utilized to enhance the features of paint film defects while avoiding the introduction of reflection noise. Finally, an improved YOLOv5 algorithm, incorporating attention mechanism feature extraction and multi-scale feature fusion, is employed to detect and classify paint film defects. Experimental results demonstrate that the proposed framework effectively reduces the reflection in paint film images, and enhances the contrast between paint film defects and the background, with a mean average precision (mAP) for defect detection reaching up to 90.13%. This work serves as a valuable reference for the automated detection of defects arising in the painting process of HST body.

Investigation on similitude method for dynamic response of high-speed train body considering thickness distortion

Small-scale model test is an economical and efficient method to study the collision process analysis and crashworthiness design of full-scale high-speed trains. For high-speed trains, the vehicle body thickness of scaled train models is too small to be processed, resulting in thickness distortion. Although the distorted model can predict dynamic responses of the full-scale model, there are some errors in predicting the dynamic response parameters. This article proposes a new similitude distortion method to improve the prediction accuracy of the high-speed train body distorted model. First, the complete similitude relationship for train collisions was derived using dimensional analysis. According to the Buckingham π theory, the theoretical expression between prediction coefficient and distortion coefficient was obtained when the high-speed train thickness distortion occurred. Then, based on a full-scale high-speed train body prototype, the benchmark model and distorted model were established. Numerical simulation was used to explore the relationship between prediction coefficient and distortion coefficient. Finally, the distorted similar model was established using the similitude distortion method. The accuracy and feasibility of this approach were verified by comparing and analysing the dynamic response curves obtained by numerical simulations between the distorted similar model and prototype. The errors of the maximum displacement and deceleration were 2.70% and 8.26%. The results show that the similitude distortion method is reliable to relate dynamic responses of scaled models to the prototype when the vehicle body thickness distorts.

Effect of surface oxide film on the performance of MIG welded joints in aluminum alloys

The effect of surface oxide film on the performance and porosity of MIG welded joints of aluminum alloy profiles for high-speed rail bodies under different ambient humidity conditions was studied. The test shows that when the humidity is low (relative humidity 5% ∼ 10%), scraping to remove the oxide film and no treatment of oxide film in both cases of the weld are well formed and flawless. The difference between the two metallurgical organization and tensile properties is not significant. In higher humidity conditions (relative humidity 40% ∼ 50%), scraping to remove the oxide film and no treatment of oxide film in both states of the weld are still well-formed. However, no treatment of oxide film welded seam with porosity, welding heat input increases can reduce the porosity. For the 6005A-T6 high-speed train body profile, when the heat input reaches 4400 J/cm, the weld such porosity disappears. However, the increase in heat input will make the tensile strength of the weld reduced by about 14%.

Acoustic optimization design of porous materials on sandwich panel under flow-induced vibration

In this study, porous sound-absorbing materials used as a lining in double-panel structure applications (such as high-speed train body structures) to limit flow-induced vibration interior noise were studied, and acoustic optimization design was performed. First, in the wavenumber domain, the cross-spectrum Corcos model was used to characterize the dynamic hydrodynamic pressure of turbulence. Biot’s theory is used to model the porous materials. The transmission loss (TL) of the sandwich panel were also determined based on the model superposition method. Three types of sandwich panel structures were considered: air–air (A–A), bonded-bonded (B–B), and bonded-air (B–A). The TL of the three structure types under hydrodynamic pressure was used to evaluate the suppression of flow-induced vibration interior noise in porous materials. The effects of flow velocity, thickness and density of the porous material, and three types of polyimide foam on the TL characteristics of the sandwich panel were investigated. The results show that the flow velocity has a significant influence on the TL of the sandwich panel. The TL of the sandwich panel decreases by 3–4 dB when the flow velocity increases by 100 km/h The B–A configuration has satisfactory sound insulation performance at most frequencies. With an increase in material thickness, the TL of the sandwich panel structure first increases and then decreases, and the material density mainly affects the TL of the structure at intermediate and high frequencies. Based on the objectives of maximizing the average transmission loss (TLavg) and minimizing the structural weight, the acoustic optimization design of the B–A structure was performed, and the balance between the two objective functions was achieved by a nondominated sorting genetic algorithm (NSGA-Ⅱ). The TLavg s of the sandwich panel structure increased by 5.2 dB when the total mass of the structure was decreased by 0.2 kg.

Jointing of CFRP/5083 Aluminum Alloy by Induction Brazing: Processing, Connecting Mechanism, and Fatigue Performance

Carbon fiber reinforced polymer (CFRP) is widely used in the lightweight design of high-speed trains due to its high specific strength. In order to further reduce the weight of the high-speed train body, it is necessary to study the joining process and fatigue properties of CFRP/aluminum alloys (CFRP/Al) structure. In this work, the CFRP plate and 5083P-O aluminum plate were successfully connected by an induction brazing method. The optimum parameters of induction brazing were determined to be an induction temperature of 290 °C, a normal pressure of 200 kPa, and a holding time of 5 s. After the 5083 plate was pre-anodized, the tensile strength of the CFRP/5083 joint reached a maximum value of 176.5 MPa. The anodization process introduced more surface micro-structures on the 5083 plate, leading to a better wetting behavior between CFRP and oxide film. Meanwhile, a new chemical bond, Al-O-C, was also formed at the interface of the CFRP/5083 joint. The fatigue limit of the CFRP/5083 joint was calculated to be 71.68 MPa through high-cycle fatigue (HCF) testing. The fatigue cracks initiated from the interface of CFRP/oxide film, and then propagated to base metal. Finally, the oxide film was peeled off from the base metal under shear stress, which contributed to the fracture of the CFRP/5083 joint. The bonding strength between CFRP and 5083 aluminum alloy is far from the conventional welded joints. Therefore, feasible approaches should be proposed to obtain a more robust bonding between CFRP and aluminum alloy in the future.

Modal characteristics analysis for car body of high-speed electric multiple units

Aiming at the problems that track irregularity and equipment operation cause complex vibration during high-speed train operation, reduce ride comfort, and affect operation safety, the modal characteristics of the vehicle body were analyzed to improve the dynamic response characteristics of the vehicle. The finite element model of the high-speed train body was established to calculate the vibration modes of the body under different mass conditions. The influence of the hanging position and hanging number of equipment under the vehicle on the modal frequency of the vehicle body was analyzed, and the variation law of modal frequency and vibration mode was obtained. Based on finite element calculation, built the vehicle body modal test system, carried out modal tests on the vehicle body, analyzed the differences and reasons between simulation and test results, and verify the correctness of numerical calculation and finite element model. The results show that the modal frequency of the car body met the relevant design standards, and the variation trend of low-order modal modes of the car body with different mass was the same. The hanging position had an obvious influence on the vertical bending of the underframe and the torsional vibration frequency of the car body. The modal frequency of the car body increased with the increase of the number of hanging points of equipment under the vehicle.

Study on hydrogen-induced stress corrosion of 7N01-T4 aluminum alloy for railway vehicles

Abstract 7N01-T4 aluminum alloy is widely applied to high speed train body material attributed to its excellent comprehensive mechanical properties; however, its high sensitivity to hydrogen stress corrosion would seriously restrict its further application. In this study, the hydrogen-induced stress corrosion of the base metal and the joint was investigated under slow strain rate test to ascertain the characteristics and mechanism of hydrogen-induced stress corrosion cracking of aluminum alloy. By applying the cathode potential, the morphology of tensile port was studied. Results show that under the action of tensile stress, the free atomic hydrogen produced in the corrosion process or absorbed hydrogen diffuses along the grain boundary into the crack tip region, weakens the grain boundary and causes hydrogen embrittlement, thus accelerating the crack propagation and fracture. These properties provide a broader prospect for the application of 7N01-T4 aluminum alloy in high-speed train body.

Robust locating research of welding fixtures for the aluminum alloy sidewall of a high-speed train body

The sidewall of a high-speed train body is welded by multiple hollow extruded aluminum alloy sheets. Due to the material characteristics of aluminum alloy, excessive welding deformation is easy to occur in the welding process of the sidewall. The welding quality of the sidewall is mainly guaranteed by fixtures, and the reasonable arrangement of sidewall fixtures can reduce the welding deformation. In this paper, two robust fixture design methods based on the Taguchi method and the double response surface method are proposed and compared. Firstly, a simplified shell finite element model of the sidewall is established and verified, and a welding deformation evaluation index of the sidewall is put forward. Secondly, based on the inside and outside table experimental design, the Taguchi method is used to design the robust parameters of sidewall fixtures, and robust locating parameters of sidewall fixtures are determined according to the SNR. Thirdly, the mean and standard deviation models of welding deformation evaluation index are established based on the double response surface method, and the robust design of sidewall fixtures are carried out with the minimization of the square sum of the mean close to the target and the standard deviation. Finally, by comparing the original scheme, the fixture design scheme based on the Taguchi method and the fixture design scheme based on the double response surface method, it shows that the robust design method of sidewall fixtures based on the double response surface method is more suitable for the robust fixture design of the sidewall. The proposed robust fixture design methods can also be applied to other similar problems.

Numerical study on the aerodynamic and acoustic scale effects for high-speed train body and pantograph

Based on computational fluid dynamics (CFD) and Lighthill acoustic analogy theory, the aerodynamics and acoustic scale effects of high-speed train bodies and pantographs are numerically studied, by changing the model scale. The model scales are 1/1, 1/2, 1/4 and 1/8 respectively. The aerodynamic force, flow field behavior, surface pressure and far-field noise of the train body and pantograph models, at different model scales are compared and analyzed. The numerical simulation is in good agreement with the experiment. The reliability of the numerical calculation method has been proven. The results show that as the scale of the model decreases, the root mean square (RMS) value and the degree of fluctuation of the aerodynamic drag coefficient of the pantograph increase. In addition, the aerodynamic drag coefficient of the train body increases, but the degree of fluctuation decreases. The similarity of the unsteady flow field of the pantograph at different model scales is strong, but the similarity of the train body is weak. The main frequency and power spectral density distribution of the pulsating pressure on the surface of the pantograph have obvious corresponding relationships with the model scale, but the train body has no obvious regularity. The longitudinal and lateral propagation characteristics of aerodynamic noise from the train body and pantograph are not affected by the model scale, but the sound pressure level changes. Compared with the train body, the far-field aerodynamic noise of the pantograph is less affected by the model scale. The energy distribution of noise is also affected by the scale of the model. As the model scale decreases, the energy concentration range of radiated noise will change from low frequency to medium high frequency.

Detection of butt weld of laser-MIG hybrid welding of thin-walled profile for high-speed train

PurposeThis study aims to solve the problem of weld quality inspection, for the aluminum alloy profile welding structure of high-speed train body has complex internal shape and thin plate thickness (2–4 mm), the conventional nondestructive testing method of weld quality is difficult to implement.Design/methodology/approachIn order to solve this problem, the ultrasonic creeping wave detection technology was proposed. The impact of the profile structure on the creeping wave detection was studied by designing profile structural test blocks and artificial simulation defect test blocks. The detection technology was used to test the actual welded test blocks, and compared with the results of X-ray test and destructive test (tensile test) to verify the accuracy of the ultrasonic creeping wave test results.FindingsIt is indicated that that X-ray has better effect on the inspection of porosities and incomplete penetration defects. However, due to special detection method and protection, the detection speed is slow, which cannot meet the requirements of field inspection of the welding structure of aluminum alloy thin-walled profile for high-speed train body. It can be used as an auxiliary detection method for a small number of sampling inspection. The ultrasonic creeping wave can be used to detect the incomplete penetration welds with the equivalent of 0.25 mm or more, the results of creeping wave detection correspond well with the actual incomplete penetration defects.Originality/valueThe results show that creeping wave detection results correspond well with the actual non-penetration defects and can be used for welding quality inspection of aluminum alloy thin-wall profile composite welding joints. It is recommended to use the echo amplitude of the 10 mm × 0.2 mm × 0.5 mm notch as the criterion for weld qualification.

Research on Vibro-acoustics of Aluminium Extrusions from a High-speed Train Body Based on Two-and-half Dimensional Finite Element/Boundary Element Method

Research on Vibro-acoustics of Aluminium Extrusions from a High-speed Train Body Based on Two-and-half Dimensional Finite Element/Boundary Element Method

Research on machining technology of complex structure parts of high-speed train body

According to the high-speed train body chassis connecting plate and the side wall key piece structure is complex, the processing difficulty is big, the processing is easy to deform, the precision is not easy to control, the processing efficiency is low, carries on the processing craft characteristic analysis, produces the processing craft analysis report. The dynamic milling forces in X, Y and Z directions during milling process are tested by means of testing and analyzing the dynamic characteristics of the machine tool, and the dynamic performance of the system can be tested by means of modal test, the transfer function of the system is obtained, and the modal parameters such as natural frequency, damping ratio and modal stiffness are obtained by mode fitting on the basis of the transfer function data, complete the dynamic characteristic analysis of the machine tool. Based on the modal analysis of the whole process system and the dynamic model analysis of the milling process, the chatter stability region of the milling process is simulated by using the theory of regenerative chatter, the results of chatter stability region related to milling process parameters are given.

Fixture Locating Modelling and Optimization Research of Aluminum Alloy Sidewall in a High-Speed Train Body

The high-speed train body is welded with aluminum alloy assemblies or parts. Due to the material properties, the welding deformation is much significant. In order to control the welding deformation, this paper takes the sidewall welding of a high-speed train body as the research objective, and carries out the fixture locating modelling and optimization research of the aluminum alloy sidewall. Firstly, a finite element model of the sidewall is established and verified by the comparison between the analysis results and the actual measurement data. Then the residual stress and deformation of the sidewall after welding are analyzed. By selecting the longitudinal parameters of different fixture locating layouts for welding analysis, models describing the relationship between the maximum welding residual stress and maximum welding deformation and the longitudinal fixture locating distance of the sidewall are established. Finally, the fixture locating model of welding deformation is used to optimize the longitudinal fixture locating distance. And the transverse fixture locating distance is also optimized by comparing different locating positions. The result shows that the welding residual stress and the welding deformation have been decreased in the optimal fixture locating layout.

Effect of different laser energy densities on the corrosion resistance of aluminum alloys

Purpose Laser cleaning, as a new type of cleaning technology, has the advantages of environment-friendliness, better selectivity, better controllability and higher efficiency compared to traditional chemical cleaning or grinding. This paper aims to use ultra-fast surface laser cleaning equipment built in laboratory to study the influence of different energy density (7.6, 11.5 and 15.3 J/cm2) on corrosion resistance of the aluminum alloy A7N01P-T4, a high-speed train body material. Design/methodology/approach SEM, white light interferometer, EDS and XPS were used to analyze the surface morphology, roughness, element content and oxide layer composition of aluminum alloy before and after cleaning. The corrosion resistance was studied by electrochemical experiments and exfoliation corrosion experiments. Findings The results showed that new oxide scale was formed on the surface after laser cleaning. The changes of surface roughness and chemical composition of oxide scale made a significant influence on corrosion behaviors. Better corrosion resistance was obtained with the energy density increased, and at the energy density of 11.5 J/cm2, aluminum alloy exhibited the best corrosion resistance. Research limitations/implications The paper only studies specific aluminum alloys and is not universal. Laser cleaning equipment is set up for the laboratory and has not yet been put into industrial production. Practical implications This paper indicated that ultra-fast laser processing was a new direction for the development of industrial equipment surface cleaning and carried out ultra-fast laser of aluminum alloy surface cleaning had certain research significance for its corrosion resistance. Social implications Compared with the conventional cleaning methods such as air abrasives grinding or chemical cleaning, laser cleaning has advantages of environment-friendliness, better selectivity, better controllability and higher efficiency. Laser cleaning can not only protect the environment, but also improve cleaning efficiency. Originality/value Changes in the surface of aluminum alloys after ultra-fast surface laser treatment were found, and the mechanism of changes in aluminum alloy corrosion properties was clarified.

Parameter analysis and optimization of welding sequence for the aluminium alloy sidewall in a high-speed train body

The sidewall is the most complex structure and welding process part in the aluminum alloy train body, and its welding deformation is greatly influenced by welding sequence parameters. In this paper, the relationship between the welding residual stress and welding deformation of the sidewall and welding sequence parameters is studied, and the optimal welding sequence is determined. Using a verified finite element model of one intercepted sidewall, the relationships between the welding residual stress and welding deformation of the sidewall and the welding of welds, welding sequences of welds and the weld sequence are studied, respectively. Some conclusions can be drawn from the analysis results. One is that the welding results at one weld are only determined by self-welding, and have nothing to do with other welds, and welding results outside one weld are affected by welds on both sides. The second is that for a single weld, the from-one-end-to-the-other welding sequence is best, and the identical welding sequence is best for each weld. The third is that the fixed welds are firstly welded and a cross weld sequence is best.

Numerical Simulation Study on Dynamic Air-tightness Thresholds Characteristics of High-speed Train Body in Mountain Area High Speed Railway

Numerical Simulation Study on Dynamic Air-tightness Thresholds Characteristics of High-speed Train Body in Mountain Area High Speed Railway

Automated Visual Inspection of Multiple Missing Fastening Bolts on the Sides of High-Speed Train Body in Railway Maintenance

The rapid development of China Railway High-speed (CRH) has provided safe and comfortable transportation for many people. The fastening bolts (FB) on the sides of CRH fall off occasionally, which might cause serious traffic accidents. However, the automatic inspection of multiple missing FBs on the sides of CRH is seldom conducted. In this study, an automated visual inspection system based on space-scale normalization is proposed to inspect the status of FBs on the sides of CRH. To locate the missing FBs in sequence images, the exact alignment of the target image and its reference image must be ensured. This problem can be solved by normalizing the target image according to its reference image. First, the FBs are located in a specific CRH region, which is called the region of interest (ROI). The target image is cropped according to the size of the ROI. Second, the keypoints are extracted and matched by using the gradient-enhanced scale-invariant feature transform (GESIFT). Furthermore, the horizontal shift between the target image and its reference image is obtained during keypoint matching. Third, the target image and its neighboring image are stitched according to the horizontal shift. Then, the target image is resegmented according to its reference image to complete the normalization of the target image. Finally, the normalized target image can be exactly aligned with its reference image. We propose an image subtraction method to locate the potential missing FBs. The FBs that may be lost are finally determined according to prior knowledge, and the state of the FBs is determined by using high-level image understanding knowledge. Experimental results show that our presented method performs excellently in monitoring the missing FBs on the sides of CRH.

Natural Aging Behavior of Double-Sided MIG Welded A7N01-T5 Aluminum Alloy

A heat treatable A7N01 (Al-Zn-Mg) aluminum alloy mainly used to fabricate high-speed train body structures was double-sided welded by MIG welding. The natural aging behavior of the joint was systematically studied by local and global mechanical property testing method. Based on TEM observation and EPMA analysis, the key factors that lead to different natural aging behavior among various regions of the joint were discussed. The global tensile strength of the joints increased obviously after natural aging. All the joint samples fractured in the weld zone, which demonstrated the weld zone was the weakest zone of the joints. And the strength of the global welds were depended on the microstructure and natural aging ability of the weld zone. Moreover, the increase of the tensile property of the three local regions in the weld zone after post natural aging decreased as Middle>lower>upper. The above phenomenon was also further confirmed by microhardness measurement. The age hardening behavior is greatly influenced by the concentration of strengthening precipitates forming element Zn. The Zn content in the weld zone determined by EPMA showed that element Zn was dispersed unevenly, which is attributed to the double V-groove design used in this work and Zn vaporization in the molten pool during welding. The Zn content in the middle layer metals is higher than that of the upper and lower layers, resulting in the remarkable hardening response for the middle layer of the weld zone during natural aging process. Additionally, the solution zone containing the same Zn content as the base metal and undergoing sufficient solid solution during welding was found to possess the high hardening ability after natural aging process.

Quench Sensitivity of AA7N01 Alloy Used for High-Speed Train Body Structure

The quench sensitivity of AA7N01 aluminum alloy used for high-speed train body structure was investigated by end-quenching test, time–temperature-transformation curves simulation, transmission electron microscopy and scanning transmission electron microscopy. The hardness decreased with the increasing distance from the quenched end, and the depth of the age hardening layer was about 50 mm. The simulation results showed that the high quench sensitivity temperature was between 230°C and 300°C and the critical cooling rate should be larger than 2°C/s. The decrease of hardness along the increasing distance from the quenched end was attributed to the coarsening of the η equilibrium phase and the widening of the precipitate-free zone. The high-angle annular dark field results provided the direct evidence of the induced-precipitation effect of Al3Zr particles during the quenching process.

Критерії і обмеження щодо визначення кута нахилу кузова швидкісного електрорухомого складу

The given paper considers problems of a dynamic impact of rolling stock on a track in curves and singles out main power factors influencing a tilt angle of rolling stock: guiding efforts, turning the crew; centrifugal force tending to tilt crew body in an outward direction; additional inertial forces called by the appearance of linear angular acceleration at crew yawing rotation. Main criteria and restrictions determining the choice of reasonable value of a high-speed train body tilt angle for railways with a gauge of 1520 mmaccording to which we can calculate tilt angle have been elaborated, namely: the provision of equal wear of rails of both lines on the basis of admitted cant of the track; the provision of the necessary comfort for passengers on high-speed trains; the provision of strength and stability of the track and safety of high-speed running; the provision of geometric blending of rolling stock in track dimensions while moving in curves.