No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Influence of Flattening in the Zone of Welded Joints of Railroad Track on Contact Interaction in the Wheel–Rail System
ResearchGate has not been able to resolve any citations for this publication.
The causes of deformation in the zone of welded joints are considered. Authors experimentally studied changes in hardness on the rolling surface of the rail in the longitudinal and transverse profiles within the thermally affected zone of the welded joint. It is established that the hardness of the rolling surface of the rail in the longitudinal direction in the thermally affected zone of the joint is uneven and is determined by the structures arising from the effects of the thermal cycles of welding and the quality of the local heat treatment. In this case, two "low spots" are clearly traced with a decrease in hardness to 290...300 HB and with a higher hardness up to 350 HB right in the welded joint. Experimentally investigated the change in the depth of the welded joint from the implemented tonnage. At the same time with strain gauge method, using the force method developed by N. N. Kudryavtsev, continuous changes in vertical forces when the wheels move along the welded joint zone were recorded. Average values of vertical forces from loaded cars were established. Experimental distributions of vertical forces were approximated by theoretical laws according to the Kolmogorov — Smirnov matching criterion. Recommendations are given on minimizing the harmful impact of rolling stock on the track in areas of lowering welded joints.
The following conclusions were made.
1. Geometry of the joint irregularity is in the form of a W-shaped deformation with an influx of metal on the receiving rail and lowering on the directing rail. The width of the upper part of the deformation varies between 160...200 mm along the axis of the rail.
2. Deformation zone of the welded joint is a source of increased dynamic impact from the wheels of the rolling stock on the elements of the upper track structure. According to the results of experimental studies it was found that the greatest increase in dynamic effects was observed from locomotive wheels up to 45.. . 70 kN, maximum values reached 180...210 kN, from the wheels of loaded freight cars the values of vertical forces increased by 35.. .45 kN, maximum values reached 145...170 kN, from the wheels of empty cars increase dynamic impacts amounted to 14...16 kN, maximum values reached 32...36 kN.
Two simulation techniques for analyzing flexible wheelset dynamics are presented. They are applied within multibody approach and implemented in "Universal mechanism" software. Equations of wheelset motion are derived using floating frame of reference and component mode synthesis methods. Modal analysis is carried out in external FEA software. Kinematics of a wheel profile is described taking into account flexible displacements of wheelset nodes. In the first techniques, Lagrangian approach is applied to obtain all terms of equation of motion including inertia forces. In the second one, Eulerian approach is simulated in the stage of integration of equation of motion. Non-rotating finite element mesh of the wheelset is considered using the interpolation of flexible displacements in the nodes. The first simulation results obtained using both approaches are presented. These results confirm correctness of the suggested techniques.
The computer simulation of railway wheelset (WS) dynamics taking into account elasticity allows analyzing WSs high frequency oscillations and vibroaccelerations of parts connected with them, modeling wheelsets strain, estimating the WS deformation impact upon force distributions in gears of locomotive drives, and also solving other problems. In the paper there are offered two approaches to the analysis of the dynamics of elastic WSs within the limits of which their finite element models with the rotating and non-rotating grid are under consideration. The WS kinematics is presented as a sum of its motion as an absolute solid together with the jointed coordinates and small elastic displacements related to modal coordinates. There are presented algorithms for the calculation of generalized forces of moving loads in the wheel/rail contact taking into account WS elasticity. The first results of modeling confirming the correctness of the methods offered are shown.
Rolling contact-fatigue damages of rails along with their wear are the most common types of rail defects. In recent years, there have been significant changes in the distribution of rolling contact fatigue damages of rails especially on railways operating under heavy haul conditions.
This paper is devoted to the overview of approaches to modeling of the occurrence of rolling contact fatigue (RCF) damages on working surfaces of rails. Four types of such approaches to modeling are considered. The first is based on the methods of contact mechanics. To realize it, the vehicle movement on the characteristic sections of the track is modeled, the forces acting in contact are determined, the contact problem is solved, and the values of the linear criterion of contact fatigue damage are determined. The required characteristics of rolling contact fatigue of the rail material are established on the basis of laboratory tests. The second approach uses the diagram of the adaptability of rail material to cyclic loads, proposed by K. Johnson, established on the basis of laboratory tests. The third approach uses criteria that have the physical meaning of the energy released at the contact as an index of the product of the tangential force in contact and relative slippage. In the fourth approach predicting the accumulation of plastic deformation under conditions of cyclic loading is performed on the basis of a series of standard tests of rail steels, including in the welded joint zone, and finite element modeling. In addition, there is also a probabilistic model, based on the assumption that it is possible to transfer the results of the RCF damage of rails on the experimental section of the road to any other site.
As the conclusion the authors formulated directions for further studies on the formation and development of surface rolling contact fatigue defects in rails.
One can only estimate the dynamic vertical impact loads under motion, since there are many effective parameters some of which are unrepresented in an equation and since the values of the considered parameters are not deterministic but estimations. Many empirical and semi-empirical equations in the literature correlate dynamic impact loads to train speed and measurable aspects of train and track components. These aspects frequently relate to track and train geometry and stiffness. However, the development of these equations relies on load and deflection measurements from particular in-service tracks or especially setup test tracks. The constants that frequently appear in these equations are particular to the conditions that generated them. Therefore, one lacks an explicit understanding of these equations unless one takes the time to investigate in detail the particular study and the particular set of data that generated these equations. Train speed limits also bound the applicability of these equations. This paper concentrates on the development of an explicit mathematical equation aimed to provide an explicit analytical estimate for the dynamic impact loads that develop on any railway track by the axles of a moving train. This paper introduces the concept of impact reduction factor and introduces a new equation that relies on the principle of conservation of energy and kinematic principles along with the impact reduction factor to estimate the impact loads generated by a moving train.
This presentation introduces the concept of impact reduction factor and a new method to estimate the vertical impact forces on railway tracks. Both the concept and the method are developed by Dr. Niyazi Özgür Bezgin.
Rail welded joints are important structural connections in the formation of continuous welded rail (CWR). Due to the difference in the stiffness and material at rail welded joints, rail damage and geometric degradation will occur and evolve under repeated train loads, which will significantly influence the wheel-rail dynamic interaction. In this paper, geometric measurements of the rail surface are made at the single flush welding zone by a tracking test on Datong-Qinhangdao heavy haul railway line in China. Fractal geometry theory is applied to calculate the fractal dimension and describe the geometric evolution of rail weld irregularities. Then, the vehicle-track coupled dynamic model is used to investigate the effect of the geometric evolution of rail weld on the wheel-rail dynamic interactions both in the time and frequency domains. The calculation results show that rail weld irregularities have fractal characteristics due to the fractal dimension of measured geometries mostly larger than 1.1. The geometry evolution of rail welded irregularity has great effects on the wheel-rail dynamic interactions in the time domain, but has little effects in the frequency domain. Fractal geometry theory can be used to describe the geometry evolution of rail weld irregularity and the effect on the wheel-rail dynamic interactions. The results can provide novel ideas for the evaluation and evaluation of the rail weld irregularity.
The presented work describes firstly the wear and crack initiation mechanism using metallographic investigations of deformed surfaces by rolling sliding wheel/rail contact. Secondly, a multi-scale finite element model is presented which allows the simulation of the deformation process near the surface of a rail under rolling sliding contact. It is necessary to model the roughness of the surfaces of wheel and rail to obtain a realistic deformation state which is comparable to experiments. Furthermore, the realistic stick-slip behavior of a rolling sliding wheel along a rail is considered. Regarding these aspects of wheel/rail contact a realistic deformation picture with near quantitative amounts of plastic shear strains from micrometer to millimeter range can be predicted. The numerical results obtained using the multi-scale model can be compared to metallographic observations and deliver a satisfying match.
The thirteen chapters of this book are introduced by a preface and followed by five appendices. The main chapter headings are: motion and forces at a point of contact; line loading of an elastic half-space; point loading of an elastic half-space; normal contact of elastic solids - Hertz theory; non-Hertzian normal contact of elastic bodies; normal contact of inelastic solids; tangential loading and sliding contact; rolling contact of elastic bodies; rolling contact of inelastic bodies; calendering and lubrication; dynamic effects and impact; thermoelastic contact; and rough surfaces. (C.J.A.)
An algorithm “Fastsim” for the simplified theory of rolling contact is described which is 15-25 times as fast as the existing programs Simrol (Kalker), and 3 times as fast as Rolcon (Knothe). The relative total force computed with Fastsim differs at most 0.2 from that calculated with Simrol, Simcona (Goree & Law), Rolcon, and the “exact” program Duvorol (Kalker). Descriptions and lists of an Algol 60, and HP 67 program version are available upon request: the Fortran IV version is given in the paper.
An engineering model for rolling contact fatigue (RCF) of railway wheels is developed. Three well-known types of fatigue in wheels – surface-initiated fatigue, subsurface-initiated fatigue and fatigue initiated at deep material defects – are accounted for. Fatigue impact is quantified by three fatigue indices expressed in analytical form. The model can easily be integrated in a multibody dynamics code without significantly increasing computational demands. A powerful tool for optimizing train–track configurations with respect to fatigue performance should result. In this paper, theoretical foundations, benefits and limitations of the model are presented. An example of a postprocessing analysis of data from a dynamic simulation of train–track interaction is given.
Solutions of three-dimensional rolling problems with slip and adhesion by variational methods
- R V Goldstein
Goldstein, R.V. et al., Solutions of three-dimensional
rolling problems with slip and adhesion by variational
methods, Usp. Mekh., 1982, vol. 5, nos. 3-4, pp. 60-102.