H.P. Yin

Influence of Road Texture on Tyre/Road Contact in Static Conditions: Numerical and Experimental Comparison

ABSTRACT This paper deals with the influence of road texture on normal pressure distribution for tyre/road contact in statics, within the framework of rolling noise prediction. A contact model is developed in statics where the tyre tread is modelled by an elastic half-space and the road surface by several perfectly rigid asperities. The problem is solved using a Two-scale Iterative Method (TIM) which is fast and efficient. The numerical results give high resolution contact patterns for real road surfaces. Predicted results are compared to contact pressures measured between a slick tyre and several road surfaces. The agreement is fairly acceptable by keeping in mind both the precision of the measurement device and the simplicity of the model. The best correlations are obtained for model surfaces composed of spherical punches and real road surfaces of moderated or high macro-texture. The results are less conclusive for road surfaces of fine macro-texture. The efficiency of the TIM at a tyre/road contact scale is an encouraging first step before introducing dynamical effects.

A dynamic analysis of a continuous welded rail track under a longitudinal stress caused by temperature changes

This article presents a dynamic computational model for analysing the correlation between rails natural frequencies and the longitudinal stress generated by temperature variation. The model includes a rail, sleepers, and the foundation. Some factors such as the rail section profile, rail wear, and the stiffness of fasteners are also considered. Based on the model, numerical computational analyses are performed. The relationship between the rails longitudinal temperature force and the natural frequency is also studied. The influences of parameters such as the wear of the rail, unsupported distance of adjoining sleepers, fastener stiffness, rail types, and foundation stiffness are investigated. A field experiment is also presented that was performed to investigate the relationship between the rails dynamic characteristics and the longitudinal stress generated by temperature variation with various unsupported sleeper spacings. The results of analysis and in-field measurements are compared.

Experimental Study of Normal Contact Force Between a Rolling Pneumatic Tyre and a Single Asperity

This paper proposes a novel experimental test apparatus that permits direct measurements of tyre/asperity normal contact forces under rolling conditions without interfacial layer. A reduced-sized pneumatic tyre is set rolling on the exterior surface of a cylindrical test rig simulating a smooth road surface except a single asperity of simple geometric shape connected to an embedded force transducer. Distinct asperity geometries lead to similar shapes of force signal but different magnitudes whose relationships with the indentation have exponents close to those in classical analytical solutions. By analyzing the time signals of the contact force and their frequency contents for different rolling speeds, the quasi-static nature of the contact, commonly assumed in numerical models, is verified.

Finite element analysis and experimental investigation of nonlinear features of rail fastening systems

The more demanding requirements for the reduction of vibration in passenger railways and urban railway lines have led to a trend towards lower-stiffness rail fastening systems accompanied by greater deformation of their rubber components. Nonlinearities under large deformation due to the boundary conditions, geometric properties, intrinsic hyperelasticity and viscidity of the rubber material, and dynamic nonlinear features such as the Payne effect have become prominent and cannot be ignored. In this research, a shear-type fastening system and a bonded compression-type rail fastening system have been designed and produced using the same rubber material. A set of mechanical experiments of the used rubber material was first performed to obtain the rubber properties; this information was later used as an input to a three-dimensional finite element model constructed using Abaqus. Laboratory tests of the two fastening specimens were then performed to obtain the quasi-static and dynamic displacement–force curves. Later, the three-dimensional finite element models were presented, and the calculated curves were compared to the measured values. Finally, the two fastening systems were comparatively analyzed, and the influences of their various nonlinear properties were discussed. The combined experimental and numerical analyses of the nonlinear properties of the two typical types of rail fastening systems are believed to enhance the understanding of their mechanical behavior and to improve the product design, structural optimization, and testing in practice.

Comparison of different tyre models for tyre/road noise applications

In terms of safety and environment, the reduction of noise generated by tire vibrations on roads has a significant importance. In order to study the vibration properties of a tire, various models have been presented in the literature. The main purpose of the current study is a brief review of the characteristics of some models. It is supposed that the tire is subjected to an excitation caused by the contact between the tire and the road. Subsequently, the dynamic behaviour of these models are studied and compared with each other. The effects of inflation pressure and the tread patterns on the dynamic behaviour of the mentioned models are examined. For verification, the dynamical behaviour of the tire is studied experimentally. Application of the present study can be contemplated in the prediction of rolling noise and rolling resistance.

Tyre/road noise: Influence of multi-asperity road surface properties on tyre-road contact stresses

This paper deals with the relation between properties of road surfaces and measured tyre/road noise. A number of artificial road surfaces composed of academic asperities of simple shapes (spherical, conical or cylindrical) are generated. The dynamical contact forces are calculated over several loops for a slick tyre rolling at different speeds. A multi-asperity contact model developed by the authors is used. The spectra for a periodic road surface clearly show that the excitation frequency of the tyre within the contact area is directly due to the speed and the distance between asperity tips in the rolling direction. For randomly distributed artificial surfaces, broad band spectra are obtained with a cut off frequency linked to distance between successive contacts in the rolling direction while the mean relative height has few influence. The results are discussed and compared with spectra of contact stresses for real road surfaces within the framework of tyre/road noise.

Numerical Computation of the Overall Moduli of Two Dimensional Infinite Media with Cracks

The overall elastic moduli of a solid are changed when the solid is damaged by cracks. For a finite solid, the size influence has been investigated and it has been found that for a given crack density, increasing crack size reduce the overall moduli [1]. For an infinite solid, it is obviously impossible to make the computation with all cracks. Classical methods suggest computing the overall moduli with the solution of the crack opening displacement of one single crack. The interaction between cracks is neglected or taken into account approximately. In this paper, the overall moduli of two dimensional infinite solids with cracks are computed numerically. From numerical simulations, it has been found that the interaction between cracks can be neglected if the distance between them is three times larger than the crack size. So one can compute the opening displacement on one crack with the presence of cracks nearby and use the crack opening displacement to compute the overall moduli. The numerical values are smaller than those of the method of diluted distribution but greater than those of the differential scheme and the self consistent method. They are also slight greater than the numerical results of bounded cracked solids. For small values of crack density however, the numerical results of both infinite solids and bounded solids are close to the estimation of the differential scheme.

Experimental study of dynamical contact forces for tyre/road noise application

This paper deals with the experimental study of tyre/road contact forces in rolling conditions for tyre/road noise investigation. In situ measurements of contact forces were carried out for a slick tyre rolling on six different road surfaces at rolling speeds between 30 km/h and 50 km/h. Contact stresses were measured at a sampling frequency of 10752 Hz using a single array of pressure sensitive cells placed both along and perpendicular to the rolling direction. The contact areas obtained during rolling were smaller than the one measured in statics. This could be due to an influence of the viscoelastic behavior of the rubber of the tyre tread during rolling. Additionally the root-mean-square of the resultant contact forces at various speeds was in the same order for a given road surface, while their spectra at various speeds were quite different. This could be explained by a spectral influence of the vibration of the tyre during rolling.

Dependence of the contact area on the velocity of a rolling tire

It is known that the eigenfrequencies of a rolling tire depend on the velocity of rotation. We distinguish two causes for the stiffness increase: the frequency dependence of the complex modulus of the materials and the geometrical stiffness. The real part of the Youngs modulus is monotonic according to the frequency. It contributes for an important part to the stiffening. The geometrical stiffness also increases with the rotational velocity. A consequence of these effects is the modification of the size of the contact area for different velocities of a rolling tire. Here we first present experimental results estimating the size of the contact area for a tire in statics and for different rolling velocities. Differences of 20% can be observed. Then the viscoelastic behaviours of the tire materials are presented and experimental results showing the frequency dependence of the complex modulus of the tire constitutive materials are given. Then finite element computations are presented with a real distribution...