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Wheel squeal is generally attributed to the lateral wheel vibration induced by lateral creepage. It should be noted, however, longitudinal creepage also exists at wheel/rail interface. Given the significance of longitudinal creepage in vehicle dynamics, a test rig that can introduce various longitudinal creepages by changing the teeth number of synchronous pulley is developed in this research, and measurement results show that squeal spectrum has three dominant peaks, whose sound pressure levels decrease with longitudinal creepage. In order to investigate the reason why longitudinal creepage can mitigate wheel squeal, a model of a wheel/rail system is developed in this research to analyse this phenomenon using complex eigenvalue method, and the results show the inner wheel tends to generate unstable vibration at three different vibration modes, correlating well with the dominant peaks of sound spectrum. Further analyses can illustrate the reason why longitudinal creepage can mitigate wheel squeal: the absolute value of effective damping ratio of each mode decreases with longitudinal creepage, so structural damping and frictional damping are less likely to be overcome by negative damping. [ABSTRACT FROM AUTHOR]

This study presents the results of modelling the rolling contact of the elastic sphere and the elastic half-space in the presence of a thin intermediate viscoelastic layer which properties are described by an elastic nonlinear Winkler body in the normal direction and a viscoelastic Maxwell body in the tangential direction. The analytical–numerical approach for the estimation of contact fatigue damage, accumulated in the elastic half-space under rolling friction conditions, is developed. The proposed model can be used, in particular, to study the effect of mechanical properties of the friction modifiers (elastic moduli and relaxation times) and its thickness as well as the relative slippage on the formation of the surface and under surface contact fatigue cracks in rails. The results of the analysis can also be applied for the estimation of efficiency of solid lubricants in rolling contacts under given operating conditions. [ABSTRACT FROM AUTHOR]

Bearing is the most vulnerable key part in rotating machine and bears important influence on the safety of equipment. Weakness and complexity are the two features of fault characteristic information carried by signals in the early stage of fault. For that, a fault is difficult to be recognized correctly. To identify a compound failure of bearing, the paper has brought forward a new self-adaptive option method for component signals that are sensitive to failure feature information of bearing. The sensitivity of kurtosis to bearing failure is exploited and the influence of signal complexity on the extraction of failure feature information is taken seriously, the paper has proposed the self-adaptive option method for component signals that are sensitive to failure feature by combined kurtosis with Complexity parameter included in Hjorth parameters. Furthermore, as the mid-value represents the general level of signal and is not affected by larger or smaller data, with the mid-values of kurtosis and Complexity parameter as the boundary, the paper has chosen the component signals which can more comprehensively show the failure features of bearing. Additionally, by principal component analysis (PCA), component signals selected are blended and reconstructed. Finally, by the Hilbert envelope spectrum of signals reconstructed, failure types of bearing are identified. To verify the effectiveness of presented method, the presented method is compared with conventional method on the basis of the exactly consistent data. The result indicates that the proposed method is superior to the traditional one in extracting fault information and identifying the multiple failure types of bearing. [ABSTRACT FROM AUTHOR]

Wheel-rail impact, which arises from structural discontinuities and short-wave defects, becomes more serious with higher train speeds and larger axle loads. The large impact load can accelerate the deterioration of vehicle-track components and induce a high level of impact noise. This paper aims to better understand the characteristics of wheel-rail impact and redevelop corresponding mitigation measures. First, a well-validated vehicle-track vertical interaction model with a singular rail defect is built up considering nonlinear Hertz contact. Then, the simulated wheel-rail impact force is characterized in both the time and frequency domains with different running speeds and defect geometries employing continuous wavelet transform. The identified characteristic frequencies are correlated to the track resonance modes. Afterward, a parameter sensitivity analysis of railpads, ballast, roadbed, and suspensions is performed to obtain the mitigation measures of wheel-rail impact. The results show that the wheel-rail impact force can be characterized by four stages in the time domain, the quasi-static stage before the impact, the forced vibration, the free vibration, and the quasi-static stage after the impact, respectively. Four characteristic frequencies are identified in the wheel-rail impact response: f 1 at 45 Hz, f 2 at 100 Hz, f 3 at 260 Hz, and f 4 at 810 Hz. Among them, f 4 has the dominant vibration energy and is determined together by the pinned-pinned resonance mode and the defect excitation frequency. Characteristic frequencies f 1, f 2, and f 3 correspond to the ballast, sleeper, and rail resonance modes, respectively, which are independent of the defect geometry. The increase of railpad stiffness can effectively reduce the maximum wheel-rail impact force and thus the impact factor. Larger railpad stiffness and damping can significantly reduce the dominant vibration energy at about 810 Hz of f 4. This work can contribute to the optimization of vehicle-track parameters for a new design of more impact-resistant railways. [ABSTRACT FROM AUTHOR]

Rail corrugation is very serious in Cologne egg fastener track; effective control measures are still lacking. The cause of the corrugation wear on a curved metro track is analyzed based on the friction-induced vibration theory. A finite element model is established to study the frequency domain and time domain features of the friction-induced oscillation of this system. The influences of the fastener spacing and the fastener support length on the corrugation wear are investigated to develop countermeasures. The simulation results show that the friction-induced vibration of the wheel-track system is the wavelength-fixed mechanism of the corrugation wear of rail of the curved Cologne egg fastener track. There are two reasons why the low rail corrugation wear is more serious. The contact resultant force between the low rail and the wheel is obviously bigger than that between the wheel and the high rail, resulting in a higher wear rate of the low rail. The contact force fluctuation of the low rail caused by the friction-induced vibration is more severe, resulting in a higher corrugation wear evolution speed on the low rail. The friction-induced oscillation cannot be eliminated only by adjusting the fastener support length and spacing. However, the long-wavelength corrugation wear instead of the more harmful short-wavelength corrugation wear can be produced by adjusting the fastener support length and the fastener spacing to alleviate the influence of corrugation wear on the vehicle-track system. [ABSTRACT FROM AUTHOR]

Based on the measured spectra of rail roughness and track structures longitudinal roughness, the rail grinding limit is studied with the help of an established coupled dynamic metro vehicle–track model and a rolling contact fatigue model. The results indicate that metro rail grinding control should be regulated according to corrugation wavelength range and operating speed. Based on the rolling contact fatigue model, longer wavelength of rail corrugation has less influence on the wheel rolling contact fatigue. For the metro lines with a maximum operating speed of 80 km/h, the average levels of rail corrugation in the wavelength ranges of 30–65 mm, 65–125 mm, and 125–250 mm should be less than 5.4, 24.8, and 33.8 dB re 1 μm, respectively; for the ones with the operating speed of 80–120 km/h, the corresponding average corrugation levels in the three wavelength ranges should be less than 4.4, 9.8, and 29.8 dB re 1 μm, respectively. [ABSTRACT FROM AUTHOR]

A method based on minimum entropy deconvolution with convolution adjustment and zero frequency filter is presented for the identification of weak faults in rolling element bearings. Localized fault present in rolling element bearings causes periodic impulses in the bearing vibration signal. The zero frequency filtering of the bearing vibration signal keeps only the localized disturbances at the impulse locations while attenuating the non-impulsive components of the signal. The effectiveness of zero frequency filtering depends on the strength of impulses present in the measured faulty bearing signal in time domain. In the present work, Minimum entropy deconvolution adjusted is used as a preprocessor to improve the strength of impulses in the measured time-domain bearing signal. The effectiveness of the proposed algorithm is tested with simulated signals for the faulty bearing vibration at different levels of added Gaussian noise. The algorithm is also validated using experimental bearing vibration dataset. Results from the proposed algorithm are compared with the results of the zero frequency filter and local mean subtraction-based technique for rolling element bearings' fault identification. The proposed algorithm performs better detection in case of a weak fault signal. [ABSTRACT FROM AUTHOR]

When a wheel rolls over a railway rail, it 'sees' a varying stiffness downwards because the rail is periodically supported by sleepers, leading to parametric excitation of the rail/wheel system. This study investigates the importance of parametric excitation on railway noise generation. Because the problem is non-stationary, it is modelled in the time domain. Rail and wheel impulse response functions, together with an iteration scheme to match boundary conditions in the rail/wheel contact patch, yield rail and wheel response plus contact force at each wheel position on the rail. Forward velocity and rotation of the elastic wheel are accounted for. Feedback coupling between response and force takes part in the excitation. Numerical simulations show that, for a rail on stiff pads, parametric excitation is a major excitation mechanism, above all leading to increased excitation and noise levels in a broad frequency region around the pinned–pinned frequency. [ABSTRACT FROM AUTHOR]