Influence of axle–wheel interface on ultrasonic testing of fatigue cracks in wheelset

For the ultrasonic testing at the wheel seat of railway axles, quantitative investigation of the reflection and transmission phenomena at the axle–wheel interface is important. This paper describes the influence of the axle–wheel interface on the ultrasonic testing of a fatigue crack in a wheelset by applying the spring interface model. The normal and tangential stiffnesses were identified experimentally for an as-manufactured wheelset at the normal incidence, and the reflection coefficient for the shear-wave oblique incidence was calculated. A parametric study was performed to clarify the influence of these interfacial stiffnesses on the incident-angle dependence of the reflection coefficient. The calculated reflection coefficient at the incident angle of 45° qualitatively explained the relative echo-height decrease due to the presence of a wheel observed experimentally for a wheelset in fatigue loading by rotating bending. The quantitative difference between the experimental and calculated results was considered to be due to the reduction of the effective interference of shrink fit by the wear at the axle–wheel interface during the fatigue loading as well as by the applied bending moment. For the estimated relative echo-height decrease to agree with the experimental results, the interfacial stiffnesses were found to be smaller than the values identified for the as-manufactured wheelset by a factor of 0.5–0.7.     

On the spin-isospin response at intermediate energies

We have calculated the response function of infinite nuclear matter to a spin-isospin probe in the transverse and longitudinal channels. The two channels are distinguished by the meson exchanged (ρ or π, respectively) in the ph and Δh interactions, in addition to the effective g′ interaction. In the intermediate-energy region the response is particularly sensitive to the Δ-dynamics in the nuclear medium. We have applied the results of a previous calculation, which is based on a self-consistent treatment of π- and Δ-propagation in nuclear matter, to obtain Δ-self-energy corrections in the medium. Due to the opening of many-body decay channels, the self-consistent mechanism supplies a strong quenching and spreading effect on the Δ-peak in the transverse channel and we find a remarkable contribution to the response function in the energy region corresponding to the dip in inelastic electron scattering. A comparison with the experimental data for the ¹²C(e, e') cross section is given. In the longitudinal channel, on the other hand, the coherent propagation of the intermediate pion has the effect of splitting the Δ-peak into two parts, due to the vanishing of the polarization propagator at the energy corresponding to the on-mass-shell pion. The self-consistent calculation again yields a quenching effect on the response which is particularly strong on the lower peak and pushes up the other one to higher energies.     

Bayesian estimation of a dynamic structure's response

This study focuses on the estimation of uncertainty associated with the stress/strain prediction procedures from dynamic test data of structural systems. An accurate prediction of the maximum response levels for physical components during in-field operating conditions is essential for evaluating their performance and life characteristics, as well as for investigating their behavior in light of system design and reliability assessment. Stress/strain inference for a dynamic system is based on the combination of experimental data and results from the analytical/numerical model of the component under consideration. Both modeling challenges and testing limitations contribute to the introduction of various sources of uncertainty within the given estimation procedure with consequent reduced confidence in the predicted response.The objective of this work is to quantify the uncertainties present in the current response estimation process by means of a Bayesian-network representation of the modeling process which allows for a rigorous synthesis of modeling assumptions and information from experimental data, as it takes into account the multi-directional nature of uncertainty propagation. More specifically, the focus is on the residual uncertainty associated with the system's inferred response, and its dependence upon the amount of test data being included in the estimation analysis.Both discrete and linear Gaussian networks were investigated with a focus on their training accuracy and performance in the presence of nonlinear relationships among the physical quantities, weak cause-effect nodal links, as well as different sensitivity levels with respect to infused evidence.     

新型三角履带诱导轮瞬态响应模拟方法与分析

针对传统的三角履带诱导轮结构一直存在动力性能不足、轴承系统负荷大、动力动态响应差的问题。提出并设计了一种新型三角履带诱导轮瞬态响应模拟方法。根据有限单元程序对数据分析设定,设计动力轴承系统。运用VENSIM仿真模型与多体动力学算法,对三角履带诱导轮结构瞬态响应进行了分析。并进行了实验分析,结果表明,传统的三角履带诱导轮瞬态响应模拟方法相比,改进的三角履带诱导轮结构具有瞬态响应快,地域适应性强,轴承系统寿命长等优点。     

Vibrational response prediction of a pneumatic tyre using an orthotropic two-plate wave model

A wave model to predict the vibrational response of a pneumatic tyre subject to line force excitation is presented. The tread and sidewalls are each modelled as thin, flat orthotropic plates with in-plane tension, which are joined together by a translational stiffness, and to a rigid rim. The dynamic response of the tyre to harmonic excitation is decomposed into spatial harmonics around the circumference, and waves in the meridional direction. At low frequencies (<100 Hz), the response is stiffness-like, and is controlled by the sidewall properties and tension effects resulting from the tyre pressure. In the mid-frequency range (100-500 Hz), a resonant response is observed, associated with modes both across and around the tyre. At high frequencies (>500 Hz), the response tends towards that of an infinite orthotropic plate. Experiments have been conducted on an inflated tyre fitted to a wheel rim to confirm the theoretical findings. The results show reasonable agreement with the predictions, the model accurately reflecting the phenomenological behaviour.     

On the impact noise generation due to a wheel passing over rail joints

Impacts occur when a railway wheel encounters discontinuities such as rail joints. A model is presented in which the wheel/rail impacts due to rail joints are simulated in the time domain. The impact forces are transformed into the frequency domain and converted into the form of an equivalent roughness input. Using Track-Wheel Interaction Noise Software (TWINS) and the equivalent roughness input, the impact noise radiation is predicted for different rail joints and at various train speeds. It is found that the impact noise radiation due to rail joints is related to the train speed, the joint geometry and the static wheel load. The overall impact noise level from a single joint increases with the speed V at a rate of roughly .     

Ground-borne vibration due to static and dynamic axle loads of InterCity and high-speed trains

In predictions of railway-induced vibrations, a distinction is generally made between the quasi-static and dynamic excitation. The quasi-static excitation is related to the static component of the axle loads. The dynamic excitation is due to dynamic train–track interaction, which is generated by a large number of excitation mechanisms, such as the spatial variation of the support stiffness and the wheel and track unevenness. In the present paper, the quasi-static excitation and the dynamic excitation due to random track unevenness are evaluated by means of numerical predictions. A solution strategy is presented that allows for the evaluation of the second-order statistics of the response due to dynamic excitation based on the power spectral density function of the track unevenness. Due to the motion of the train, the second-order statistics of the response at a fixed point in the free field are non-stationary and an appropriate solution procedure is required. The quasi-static and dynamic contribution to the track and free-field response are analysed for the case of InterCity and high-speed trains running at a subcritical train speed. It is shown how the train speed affects the quasi-static and dynamic contribution. Finally, results of numerical predictions for different train speeds are compared with field measurements that have been performed at a site along the high-speed line L2 Brussels–Köln within the frame of homologation tests.     

On the particle dynamics in a dynamic billiard

We have analyzed the dynamics of a classical point particle experiencing elastic reflection from a single periodically oscillating wall and in a dynamic billiard system with reflections from stationary and oscillating walls. In the case of a single wall, the attachment regime is demonstrated in which the particle is almost localized at the wall during a half-period of oscillations and undergoes multiple reflections from it. It has been shown that, when the parameters of the problem are varied in a range that corresponds to a change in the number of consecutive reflections from the same wall, the dependence of the velocity of the reflected particle on these parameters includes discontinuities of the derivative. For the dynamic billiard system, stable regimes of various types with invariable kinetic energy of the particle, as well as regimes of deterministic chaos, have been considered; in the latter case, these discontinuities also play a significant role.     

On the dynamic theory of a focusing Cauchois spectrometer

A dynamic theory of Laue diffraction of X-ray wave from a perfect bent crystal in the Cauchois scheme is presented. The cases of spherically divergent and converging waves are considered. The spectral resolution of a focusing Cauchois spectrometer is estimated.     

Static and dynamic stability of pneumatic vibration isolators and systems of isolators

Pneumatic vibration isolation is the most widespread effective method for creating vibration-free environments that are vital for precise experiments and manufacturing operations in optoelectronics, life sciences, microelectronics, nanotechnology and other areas. The modeling and design principles of a dual-chamber pneumatic vibration isolator, basically established a few decades ago, continue to attract attention of researchers. On the other hand, behavior of systems of such isolators was never explained in the literature in sufficient detail. This paper covers a range of questions essential for understanding the mechanics of pneumatic isolation systems from both design and application perspectives. The theory and a model of a single standalone isolator are presented in concise form necessary for subsequent analysis. Then the dynamics of a system of isolators supporting a payload is considered with main attention directed to two aspects of their behavior: first, the static stability of payloads with high positions of the center of gravity; second, dynamic stability of the feedback system formed by mechanical leveling valves. The direct method of calculating the maximum stable position of the center of gravity is presented and illustrated by three-dimensional stability domains; analytic formulas are given that delineate these domains. A numerical method for feedback stability analysis of self-leveling valve systems is given, and the results are compared with the analytical estimates for a single isolator. The relation between the static and dynamic phenomena is discussed.     

On the vibration transmission of a rolling tire on a suspension system due to periodic tread excitation

Several methods of modeling the vibration excitation of an automotive tire by its tread pattern were developed, ranging from a very simplified approach with an equivalent single point, single line scanning procedure to multi-point, multi-line scanning. This results in a periodic model, since even for a so called random tread pattern there is a periodicity corresponding to one tire revolution. Various tread profiles are explored and response spectra for forces and displacement at the suspension point are obtained and discussed. Receptances formulated in terms of the free tire shell modes are utilized. To contrast the force input type models of the tread excitation with the displacement type input of long road waves, the latter is also discussed briefly.