A critical review of wheel/rail high frequency vibration-induced vibration fatigue of railway bogie in China

Purpose–This review aims to give a critical view of the wheel/rail high frequency vibration-induced vibration fatigue in railway bogie.Design/methodology/approach–Vibration fatigue of railway bogie arising from the wheel/rail high frequency vibration has become the main concern of railway operators.Previous reviews usually focused on the formation mechanism of wheel/rail high frequency vibration.This paper thus gives a critical review of the vibration fatigue of railway bogie owing to the short-pitch irregularities-induced high frequency vibration,including a brief introduction of short-pitch irregularities,associated high frequency vibration in railway bogie,typical vibration fatigue failure cases of railway bogie and methodologies used for the assessment of vibration fatigue and research gaps.Findings–The results showed that the resulting excitation frequencies of short-pitch irregularity vary substantially due to different track types and formation mechanisms.The axle box-mounted components are much more vulnerable to vibration fatigue compared with other components.The wheel polygonal wear and rail corrugation-induced high frequency vibration is the main driving force of fatigue failure,and the fatigue crack usually initiates from the defect of the weld seam.Vibration spectrum for attachments of railway bogie defined in the standard underestimates the vibration level arising from the short-pitch irregularities.The current investigations on vibration fatigue mainly focus on the methods to improve the accuracy of fatigue damage assessment,and a systematical design method for vibration fatigue remains a huge gap to improve the survival probability when the rail vehicle is subjected to vibration fatigue.Originality/value–The research can facilitate the development of a new methodology to improve the fatigue life of railway vehicles when subjected to wheel/rail high frequency vibration.

A high frequency vibration compensation approach for ultrahigh resolution SAR imaging based on sinusoidal frequency modulation Fourier-Bessel transform

Ultrahigh resolution synthetic aperture radar(SAR)imaging for ship targets is significant in SAR imaging,but it suffers from high frequency vibration of the platform,which will induce defocus into SAR imaging results.In this paper,a novel compensation method based on the sinusoidal frequency modulation Fourier-Bessel transform(SFMFBT)is proposed,it can estimate the vibration errors,and the phase shift ambiguity can be avoided via extracting the time frequency ridge consequently.By constructing the corresponding compensation function and combined with the inverse SAR(ISAR)technique,well-focused imaging results can be obtained.The simulation imaging results of ship targets demonstrate the validity of the proposed approach.

Graphene aerogel-based vibration sensor with high sensitivity and wide frequency response range

Compared with piezoresistive sensors,pressure sensors based on the contact resistance effect are proven to have higher sensitivity and the ability to detect ultra-low pressure,thus attracting extensive research interest in wearable devices and artificial intelligence systems.However,most studies focus on static or low-frequency pressure detection,and there are few reports on high-frequency dynamic pressure detection.Limited by the viscoelasticity of polymers(necessary materials for traditional vibration sensors),the development of vibration sensors with high frequency response remains a great challenge.Here,we report a graphene aerogel-based vibration sensor with higher sensitivity and wider frequency response range(2 Hz–10 kHz)than both conventional piezoresistive and similar sensors.By modulating the microscopic morphology and mechanical properties,the super-elastic graphene aerogels suitable for vibration sensing have been prepared successfully.Meanwhile,the mechanism of the effect of density on the vibration sensor’s sensitivity is studied in detail.On this basis,the sensitivity,signal fidelity and signal-to-noise ratio of the sensor are further improved by optimizing the structure configuration.The developed sensor exhibits remarkable repeatability,excellent stability,high resolution(0.0039 g)and good linearity(non-linearity error<0.8%)without hysteresis.As demos,the sensor can not only monitor low-frequency physiological signals and motion of the human body,but also respond to the high-frequency vibrations of rotating machines.In addition,the sensor can also detect static pressure.We expect the vibration sensor to meet a wider range of functional needs in wearable devices,smart robots,and industrial equipment.

Influence of High Frequency Vibration on Deep Drawing Process of AZ31 Sheet at Room Temperature

Quasi-ultrasonic vibration with a frequency of 15 kHz and a maximum output of 2 kW was imposed on the deep drawing process of AZ31 magnesium alloy sheet at room temperature,in order to reveal the effect of high frequency vibration on deformation behavior of AZ31 during the process.From the drawn results and the observation of the microstructure within the large deformation area,high frequency vibration has a great influence on the formability,the forming load and the failure mode of AZ31 sheet during the deep drawing process;the influence is a comprehensive result of so-called "volume effect" and "surface effect",and relies on the vibrating amplitude.Total forming load decreased significantly as soon as the vibration superimposed.According to the tensile test results of AZ31 bars under ultrasonic vibration,the formability of AZ31 sheet increases firstly with the increase of stimulating energy,then decreases and finally becomes brittle.Under the combined influence of "surface effect" and the "softening" in the "volume effect" near the relative low amplitude of 25%A in the experiment(A is the maximum amplitude),the formability of AZ31 reaches the largest value,and the samples possess the same distribution trend of cracks as those added with lubricating oil.With the increase of excitation energy,the "volume effect" gradually becomes apparent,and finally the "hardening" of the "volume effect" occupies a dominant position.

Mesoplasticity Approach to Studies of the Cutting Mechanism in Ultra-precision Machining

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.