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• A long-term experimental study investigated abnormal carbody lateral low-frequency vibrations in intercity EMU trains. • High abrasive block hardness, continuous high-pressure mode, and frequent stops caused double-hollow wear on wheel profiles. • Double-hollow wear reduced wheel-rail contact conicity, leading to carbody hunting and resulting in abnormal vibration. • Mitigation by reducing abrasive block hardness and switching to low-pressure intermittent mode was confirmed by experiments. Abnormal low-frequency lateral vibrations of the carbody present a significant issue in commercial train operations, severely affecting passenger comfort and potentially compromising operational safety. This is usually linked to carbody hunting, triggered by low equivalent conicity early in the wheel re-profiling cycle. However, in this study, it was observed during the later stages of the wheel re-profiling cycle in conjunction with atypical wear patterns in an intercity EMU train. To investigate the underlying causes, a long-term experimental study was conducted, tracking both carbody vibrations and wheel profile wear. A detailed vehicle dynamics model was developed to analyze the mechanism behind the phenomenon. The study identified that the combination of high hardness in the abrasive blocks of the tread cleaning device, high-pressure continuous operation, and the frequent start-stop cycles characteristic of intercity trains collectively contributed to the development of a double-hollow wear pattern on the wheel profile. This wear pattern reduced equivalent conicity, leading to carbody hunting phenomenon, resulting in a 1 Hz lateral harmonic vibration. To mitigate this issue, the hardness of the abrasive blocks was reduced, and their operation mode was adjusted to low-pressure intermittent operation. Validation through a subsequent re-profiling cycle demonstrated that these modifications effectively shifted the wheel profile to a single-hollow wear pattern, increased equivalent conicity, and prevented the recurrence of abnormal vibrations. This research provides essential insights and practical solutions for railway engineers seeking to mitigate carbody hunting, thereby enhancing operational safety and passenger comfort. [ABSTRACT FROM AUTHOR]

• The abnormal noise inside the cabin is caused by the misalignment of the shaft coupling in the transmission system. • Shaft coupling misalignment can induce alternating meshing forces in the gears, resulting in abnormal vibration and noise. • The mechanism of abnormal noise generation was revealed by establishing an electromechanical coupling model. • Replacing the coupling effectively resolves the issue of abnormal noise. This study conducts on-site testing and simulation analysis of the abnormal noise phenomenon generated during the operation of high-speed trains. The sound pressure characteristics in the cabin and the vibration of different vehicle components are recorded and subjected to comprehensive analysis. Test results indicate that significant abnormal noise occurs inside the cabin at the speed of 250 km/h, with frequencies of 87 Hz, 173 Hz, 259 Hz, and 346 Hz. Through sound source identification, vibration transmission analysis and theoretical derivation, it has been determined that the abnormal noise primarily originates from the transmission system, and it is further speculated that these abnormal vibrations and noises may be correlated with the shaft coupling misalignment within the transmission system. To verify the conjecture, a high-speed vehicle electromechanical coupling simulation model was established, incorporating the shaft coupling misalignment in the transmission system. The vibration characteristics of vehicle components were analyzed, confirming that shaft coupling misalignment leads to uneven meshing forces in gears, resulting in significant vibration and noise that affect the riding comfort of the vehicle. We propose replacing the shaft coupling to solve this problem, the test results showed that the abnormal vibration amplitudes of the transmission system at 87 Hz, 173 Hz, 259 Hz, and 346 Hz were significantly reduced after replacing the shaft coupling, and the amplitude of the corresponding frequencies on the cabin floor decreased by 91 %, 78 %, 98 %, and 66 %, respectively. The issue of abnormal noise has been effectively resolved. [ABSTRACT FROM AUTHOR]

• The essential and induced causes of steel spring failure are revealed. • The fatigue behavior and fatigue life of 60Si2CrVAT springs are investigated. • The effect of decarburization on the fatigue strength is fatal. • Double-layer nonlinear vibration damping fasteners can reduce steel spring vibration. • Improvements measures to extend the fatigue life of steel springs are proposed. This study investigates the fatigue failure behavior of coil compression springs and various influencing factors. The intrinsic and induced causes of fatigue failure in metro steel springs were revealed by systematic tests. Macroscopic observation and metallographic analysis of the fracture indicate that decarburization, which leads to a reduction in the fatigue limit of the material, was the essential cause of the failure. The resonance of the steel spring caused by rail corrugation leads to an increase in dynamic stress, which is the induced cause of the failure. The combined effect of the two factors promoted the failure of the springs. In addition, decarburization led to a decrease in the microhardness of the spring surface from 462 HV to 151 HV and a decrease in fatigue life from over 3.6 million kilometers to 521,000 km (with the decarburization depth of 0.3 mm). The effects of different stress ratios and decarburization depths on the equivalent shear stress (ESS) were comprehensively investigated. The ESS of steel springs with decarburization and different stress ratios were calculated according to the FKM Guideline and the EN 17149 standard. The ESS decreases from 188 MPa to 77 MPa at a stress ratio of R = 0, and from 168 MPa to 76 MPa at a stress ratio of R = 0.5. If the effects of rail corrugation are not taken into account, the ESS meets the design life requirements. Furthermore, the effects of different rail fastener types and track structures on the dynamic stress were compared. It was found that the double-layer nonlinear vibration damping fasteners can significantly improve steel spring vibration. Finally, improvement measures and recommendations are proposed based on the root causes of failure and the influencing factors. [ABSTRACT FROM AUTHOR]

The high-temperature heat damage is mainly caused by heat dissipation of surrounding rock in deep mining of mine, so spraying thermal insulation layer (TIL) on mine roadway can be used to actively heat insulation. As a kind of green material, bamboo branches have excellent thermal insulation and mechanical properties. In this paper, gravel and ceramsite were used as aggregate, bamboo branches and glass hollow bead were used as main thermal insulation materials, and the effects of different content, diameter, and length of bamboo branches on mechanical properties, thermal insulation properties, and microstructure were studied through orthogonal experiments. A group of specimens with the best comprehensive performance was selected through the analysis of the efficiency coefficient, and the optimal ratio was determined. This ratio ensures the perfect balance between insulation and strength for TIL, which is essential for the preparation of TIL. At the same time, the numerical simulation software Fluent was used to establish the roadway model, and the cooling effect of the TIL on the airflow temperature in the roadway under different working conditions was studied based on the parameters of the selected specimens. These parameters are based on the actual characteristics of the specimen, and their accuracy ensures the reliability and validity of the research results. The results show that under the optimal mixing ratio, the thermal conductivity (TC) of the specimen is 0.224 W/(m·K), the thermal insulation performance of the prepared coating is increased by 25∼65 %, and the mechanical strength is also improved. The optimal mix ratio obtained in this study can be applied to the field of mine thermal damage control, and the feasibility of natural bamboo branches for preparing roadway thermal insulation material is demonstrated. Bamboo branches grow rapidly, and their use as thermal insulation materials will not only not cause a burden on the environment, but help to promote ecological recycling and achieve sustainable use of resources. • The natural bamboo branches are innovatively prepared into a new type of mine thermal insulation material. • The thermal insulation performance of the prepared material is only 12.8 % of that of ordinary cement mortar. • Effect of thickness, airflow temperature and wind speed on cooling of thermal insulation coating. [ABSTRACT FROM AUTHOR]

Abstract In order to fill up the deficiency of dynamic impact characteristics and damage mechanism of 7055 aluminum alloy. Johnson-Cook constitutive equation and damage model for 7055 aluminum alloy was established. Dynamic impact performance is studied using experimental and simulation methods. Results show that: Under 120 °C, the microstructure of the alloy changed notably after dynamic shock, the number density of η ′ precipitated phases reduced appreciably as the shock strain rate increased; Under 220 °C, the number density of the η ′ precipitated phases in the testpiece reduced significantly after shock when the strain rate of dynamic shock was 6000s-1; Under 220 °C, as the shock strain rate increased, almost all the η ′ precipitated phases turned into a η phase incoherent to the aluminum matrix. At the same time and velocity, the stress after dynamic shock is the largest when the dynamic temperature is 220 °C; when the ambient temperature is 120 °C, the stress after dynamic shock is the smallest, and the stress after dynamic shock at 220 °C is twice as big as that at 120 °C. Highlights • This study is intended to examine the behavior and damage mechanism of 7055 aluminum alloy under dynamic shock, an area rarely reached by previous studies. • Dynamic shock test was conducted on high-strength aeronautical 7055 aluminum alloy under a wide range of temperature and strain rate to examine the formation of adiabatic shear bands. • Johnson-Cook constitutive equation and damage model for 7055 aluminum alloy was constructed. [ABSTRACT FROM AUTHOR]

• An anti-disturbance method for on-board detection of early wheel polygonal wear. • A weighted angle-synchronous moving average method filters out typical disturbances. • A method can identify early wheel polygonal wear through the axle-box acceleration. Wheel polygonal wear (WPW) on-board detection based on axle-box acceleration (ABA) is a critical instrument for railway wheel maintenance. However, early WPW on-board detection under typical disturbances such as rail defects is still difficult to achieve. To face this challenge, this study proposes a weighted angle-synchronous moving average (WASMA) anti-disturbance filtering for WPW on-board detection. Starting with the gear mesh component, the accurate instantaneous phase of the wheelset is calculated using a phase demodulation and time–frequency ridges combination. The ABA is then filtered using WASMA to suppress typical disturbances while revealing the features of early WPW. Simulation and field tests were carried out to verify the proposed detection method. The results demonstrated that the proposed method effectively filters out typical disturbances, such as random track irregularity, sleeper passing impact, and structural resonance, reducing the misdiagnosis of early WPW. [ABSTRACT FROM AUTHOR]

• Based on a large number of field tests and investigations, the root cause of the failure of the cowcatcher was found. • Through theoretical derivation and numerical simulation, a modal difference frequency design method is proposed. • A random vibration model was proposed instead of the full-scale rigid-flexible coupled dynamic model of the vehicle system. • The improved structure of the cowcatcher effectively prolongs the fatigue life and meets the design requirements. Cowcatchers are used in metro vehicles to remove obstacles on the track. The failure of the cowcatcher will seriously affect the safety and reliability of the train. This paper investigated the fatigue failure of cowcatchers of metro vehicles induced by the high frequency vibration through both field tests and numerical simulations. The dynamic stress, acceleration, and eigenmode of a cowcatcher as well as the wheel out-of-roundness (OOR) were measured to identify the primary factor of the fatigue failure of cowcatchers. The investigation results indicate that the main cause of the premature fatigue fracture of cowcatchers is the first-order bending eigenmode of the cowcatcher (95.4 Hz) excited by rail corrugation with the passing frequency of approximately 95 Hz. A modal differential frequency design method was proposed to improve the design of cowcatcher. The first-order natural mode frequency of the re-designed cowcatcher increases from 95.4 Hz to 160 Hz, which can effectively avoid the serious vibration excited by rail corrugation. Subsequently, a random vibration model was proposed to evaluate the effects of the improved cowcatcher. The acceleration measured in the field was used as the input of the model to reproduce the vibration environment of the cowcatcher. The model was validated by the measurement result of dynamic stress of the original cowcatcher. The fatigue life of the improved cowcatcher was calculated by the model. Compared with the original cowcatcher, the service life of the improved cowcatcher is greatly improved. [ABSTRACT FROM AUTHOR]