Stresses In Rails Research Articles

Towards a laser-vibrometry technique for measuring railroad rail stress

There is a broad consensus on the need for cost-effective and reliable methods for measurement of axial stress in railroad rails. Constrained thermal expansions and contractions induce large forces which in turn lead to bucklings and rail breaks. We are developing a new method for such measurements, based on the decrease (increase) of effective dynamic flexural rigidity under the influence of compressive (tensile) loads. Scanned laser vibrometry measurements of vibration fields at a prescribed frequency, followed by a comparison with guided wave theory for the complex cross section of the rail, allows the extraction of flexural wavenumbers. These wavenumbers are in turn related to contained load and to the rail’s intrinsic rigidity. Here we report the ongoing status of this work, describing the results of extensive laboratory measurements on unloaded rail, and test-bay measurements on rails subjected to compressive loads to 100 kip.

A vibration technique for measuring railroad rail stress

Longitudinal rail stress, related to constrained thermal contractions and expansions, leads to broken and buckled rails, and consequent service delays and derailments. There is a broad consensus on the need for cost-effective and reliable methods for the measurement of rail stress. Vibration techniques for assessing rail stress, based on the effect of longitudinal force on the free vibrations of beams, have long been proposed. It is well understood that compressive stresses decrease the flexural frequencies, while tensile stresses increase them. Past efforts attempting to use this for measurements of stress in railroad rails have failed due to an inability to control or adequately measure other parameters, most particularly the placement and stiffness of the supports. We are developing a new method in which the influence of support parameters should be minimal. Scanned laser vibrometry measurements of vibration fields, followed by a comparison with guided wave theory for the complex cross section of the rail, promises to allow the stress to be determined with the requisite precision. Here we report on the status of this work. [Work supported by Association of American Railroads and the Transportation Research Board.]

The Effects of Service Lifetime and Duty on the Residual Stress in Railway Rails

The effects of differing service lifetimes and conditions on the wear profiles, microstructural development, mechanical properties, and residual stress in railway rails was studied. The rail material was BS 113A grade 220, the most common grade used in the UK. A specimen of unused rail, fabricated under identical conditions, provided a control specimen against which all changes could be assessed. Careful metallographic examination, confirmed by microhardness profile measurement, showed the development of a stable, heavily deformed layer of 5 mm thickness below the rail head and gauge corner, irrespective of service lifetime. The residual stresses were measured in cross sections through the rail and on the rail head by a combination of magnetic techniques, known as MAPS [1] . The measurements showed that for rails of short service life the stresses across the whole rail head are principally compressive, balanced by tensile stresses within the body of the head. The largest compressive stresses are found at the gauge corner. However, for rails of increasing service life, there is a transition to tensile stresses in the gauge corner, accompanied by extensive gauge corner cracks. It is thought that the presence of the tensile residual stresses causes the cracks to initiate and propagate. New rails, on the other hand, had a tensile residual stress in the head, generated by the straightening process.

Enhanced 3D analysis of residual stress in rails by physically based fit to neutron diffraction data

The paper demonstrates applications of a new hybrid, experimental-numerical approach for studying 3D residual stress patterns in railroad rails. The new approach consists of two techniques developed at the Cracow University of Technology: an original sectioning scheme called as the transverse/oblique slicing (T/O-S) technique and a 2D physically based data smoothing/enhancement procedure called as the global method (GM). Both these methods were developed, tested and validated beforehand, presently their joint potential for analysis of real experimental data and benefits they bring will be shown. It will be done for an exemplary experimental data obtained upon actual destructive testing of rails by the neutron diffraction (ND) method performed in USA.

Residual stress formation during the roller straightening of railway rails

Residual stresses in rails due to roller straightening have become increasingly important since they are going to become part of rail purchase specifications. Both experimental and numerical investigations have been carried out in the past to reveal the formation of, primarily, the dominant longitudinal residual stresses. Most experimental evaluations show a typical C-shaped stress distribution in the rail cross section where the numerical studies do not provide a clear picture. A new and more realistic numerical simulation for the roller straightening process of rails will be presented. The model also considers the longitudinal movement of the rail through the straightener. Chaboche's multiple component non-linear kinematic hardening model has been used to account for the plastic behavior of rail steel. The results are in good agreement with the experimental investigations.

The Measurement of Residual Stress in Rails

StrainVolume 37, Issue 1 p. 9-13 The Measurement of Residual Stress in Rails L. Drewett, L. Drewett Corus Research, Development & Technology Swinden Technology Centre, Moorgate, Rotherham, S60 3ARSearch for more papers by this author L. Drewett, L. Drewett Corus Research, Development & Technology Swinden Technology Centre, Moorgate, Rotherham, S60 3ARSearch for more papers by this author First published: 29 October 2008 https://doi.org/10.1111/j.1475-1305.2001.tb01214.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume37, Issue1February 2001Pages 9-13 RelatedInformation

Residual stresses in new rails

A 3D finite element simulation is presented to calculate the residual stresses which develop during the roller straightening process of railway rails. Since this type of process simulation with contact and plasticity is very time consuming, a special simplification is used to stay within reasonable computing times. The finite element package ABAQUS was used for the analysis.

Determination of stress in ferromagnetic steel by potential drop measurements

A technique has been investigated in which absolute stress inferromagnetic materials can be determined by measurements of the response to injected current steps in parallel with the stress direction. Pairs of transient potential drop response signals, measured under various bias magnetic conditions, are the basis for calculating a parameter representing the stress in the material. Calibration curves, involving the above mentioned parameter as a function of stress, are very close to being linear, at least in the tested range of — 200 MPa (compression) to 250 MPa (tension). The observations in the described experimental work can to some extent be explained by the theory on the relationship between stress and magnetic properties. Further investigations related to the problem of the determination of stress in railway rails are planned.

Residual stresses in rails due to roll straightening

The knowledge of residual stresses in rails due to roll straightening has become increasingly important for the evaluation of the fatigue behaviour of rails. The residual stresses are induced both by the bending process and the roll contact leading to a very complicated distribution especially near those parts of the surface where the roll contact had taken place. So far, no clear picture has emerged with respect to the residual stress field, either from experiments or from simulations. This study intends to clarify the residual stress distribution by simulation with a fully three‐dimensional model taking into account both the bending and contact process. This work shows that especially in those areas where the roll contact happens compressive residual longitudinal stresses appear on the surface. Furthermore, a very steep gradient of the residual longitudinal stress distribution near the surface is observed which is reported also in very recent X‐ray and neutron diffraction experimental investigations.

Electromagnetic acoustic resonance and materials characterization

Abstract This paper reviews the operation principles and several applications of electromagnetic acoustic resonance (EMAR). EMAR is an emerging ultrasonic spectroscopy technique for nondestructive and noncontact materials characterization, relying on the use of electromagnetic-acoustic transducers (EMATs) and the superheterodyne circuitry for processing the received reverberation signals excited by long radio-frequency (RF) bursts. The transduction occurs through the Lorentz force mechanism and, for ferrous metals, the dynamic response of magnetostriction and the magnetic force as well. Weak coupling of the EMATs is now essential to realize the high accuracy of measuring ultrasonic velocities and attenuation in conducting materials. High signal to noise ratio is achieved by receiving the overlapping coherent echoes at resonant frequencies. Small changes in the related material properties are well detectable. The spectral response can be interpreted for simple geometries such as plate, cylinder and sphere. EMAR has been proven to be powerful for industrial purposes because of its robustness, the omission of surface preparations and the capacity for simple measurement in a short time. Stress application varies the propagation velocities of ultrasonics and then shifts the resonant frequencies in longitudinal and shear modes in the parallel-sided geometries. Promising applications include the two-dimensional stress distribution in thin plates, the axial stress in railroad rails and the residual stresses around the weldments. In addition, the attenuation is precisely measurable at resonant frequencies and can evaluate the grain size of polycrystalline metals. Furthermore, the EMAR technique serves for developing the basic research on the effects of the metallurgical changes on ultrasonics, leading to the damage estimation of the fatigued, crept or thermally aged metal parts.

Residual stresses in alumino-thermic welded rails

Neutron strain scanning has been used to map the residual stress field that is generated in a railway rail by a standard gap alumino-thermic weld made using routinely specified procedures. The longitudinal and vertical residual stress fields in the sections well away from the weld are characteristic of many unwelded rails, being generally tensile in the head and foot with balancing compression in the web. In the vicinity of the weld the residual stress patterns are very different. At the top and bottom surfaces of the rail the longitudinal residual stress field is strongly compressive, which is generally beneficial in that it would tend to inhibit the initiation and propagation of fatigue cracks from surface defects. Just at the surface the vertical residual stress attenuates to zero but internally, in the web region, both longitudinal and vertical components of the residual stress field are strongly tensile, which increases the susceptibility of that region to crack initiation and propagation from internal material defects. This pattern is consistent with practical operating experience, which is that most of the small proportion of alumino-thermic welds that do fail do so as a result of porosity or inclusions in the weld. It is found that the ‘boundaries’ of the ‘weld type’ residual stress fields do not coincide with the boundary of the weld, nor of the heat-affected zone, but correlate reasonably well with the positions of the extremities of the mould assembly and with the location of the steepest longitudinal temperature gradients.

Experimental study of three-dimensional residual stresses in rails by moiré interferometry and dissecting methods

Residual stresses in rails produced by rolling cycles are studied by a destructive testing procedure. Thin slices of rails are cut and small grid elements are made by cutting slots onto the surface of the slice. Residual stresses are believed to be released near the surface of the slice when those grid elements have right angles and are sufficiently small. The resulting deformation produced by the stress relief is measured by moiré interferometry. On assuming all strain components be constant along the longitudinal axis of the rail and this axis is one principal direction, three-dimensional strain and stress components are solved.

New experimental approach for studying residual stresses in rails

The distribution of residual stresses in the head of a rail produced by rolling cycles is investigated by dissection and non-dissection methods. In the dissection method, small grid elements are formed on the surface of the rail slice by slot cutting. The residual stresses are relieved by the cutting process. In the non-dissection method, residual stresses are relieved by an elevated temperature. The relieved residual deformations are detected by moiré interferometry for both methods. The results obtained by both methods are compared and the non-dissection method is recommended.

Reconstruction of residual stresses in railroad rails from measurements made on vertical and oblique slices

The paper addresses the problem of experimental determination of the residual stress state in railroad rails. A new and original method of rail residual stress examination is proposed. The novelty of the method, which is called “oblique slicing technique”, is based on its mechanical, experimental and numerical foundation. Although the new procedure can be seen as a variation on the well known and established in the field Battelle 3D technique (sometimes called Battelle slicing technique), it actually redefines the previous concepts and approaches, bringing a seemingly unparalleled means for determining the 3D stress state in railroad rail by examination of two (or more 1) 2D states measured on thin slices cut out from the rail length at different inclination angles. The paper presents a unique mechanical algorithm of restoring the full 3D stress state in the rail as if it had not been cut, and its numerical implementation is complemented with previously developed proprietary techniques of physically based approximation and/or data smoothing. The whole approach is based on moiré interferometry measurements. Apart from theoretical considerations, the paper shows some results of an extensive range of tests carried out on simulated experimental data. The purpose of the tests is to evaluate the technique on a benchmark problem and answer some technical questions. Finally, possible extensions and/or modifications as well as future research plans are discussed.

Advanced ultrasonic method for measuring rail axial stresses with electromagnetic acoustic transducer

This paper explores the feasibility of the acoustoelastic birefringence method for monitoring the axial stresses in the railroad rails. An electromagnetic-acoustic transducer (EMAT) is incorporated with a superheterodyne-phase-sensitive detector to accomplish noncontacting stress measurements. Two different measurement techniques are employed and compared to each other, both of which use the polarized shear waves propagating transversely to the rail axis. One is the pulsed resonance spectroscopy technique applied to the web, where the surfaces are nearly parallel to each other and support the thickness oscillations. The other method detects the small phase shift that occurs along with the stress application. The phase shifts were measured for the discrete reflection echoes that traveled long distances (top-to-bottom echo and multiple echoes in the head of the rail). The compressive axial load was raised up to 60 tons with the Shinkansen (bullet train) rail samples, which exceeds the buckling load of long rails. Both techniques showed a linear response to stress with a sufficient sensitivity and robustness, which promise the development of a practical railroad maintenance technology. The effects of the liftoff and the residual stress distribution are determined.

破壊力学 レールの腹部ぜい性き裂進展特性とその影響因子の解明

Propagation Characteristics of rail web-cracking has been discussed in connection with residual stress in rails. To clarify the effect of residual stress on rail web-cracking, several testing methods for rail web-cracking were examined first and a DWWT (Drop Weight Wedge Test) method with high accuracy and good reproducibility was newly proposed. Secondly, by using this test method, the rail web-cracking properties of several kinds of rails were evaluated. DHH rails and NHH rail which were hardened by heat-treatment showed better web-cracking properties than the standard carbon rail and low alloy rail which were straightened by a roller straightenner. This is caused by the differeces in distribution and longitudinal residual stress between the head and the base in rails.Furthermore, the relationship between the propagation length of web-crack and the amount of opening value on cut mouth by saw cutting along the rail web was discussed.

Advanced Ultrasonic Method for Measuring Rail Axial Stresses with Electromagnetic Acoustic Transducer

Abstract This paper explores the feasibility of the acoustoelastic birefringence method for monitoring the axial stresses in the railroad rails. An electromagnetic-acoustic transducer (EMAT) is incorporated with a superheterodyne-phase-sensitive detector to accomplish noncontacting stress measurements. Two different measurement techniques are employed and compared to each other, both of which use the polarized shear waves propagating transversely to the rail axis. One is the pulsed resonance spectroscopy technique applied to the web, where the surfaces are nearly parallel to each other and support the thickness oscillations. The other method detects the small phase shift that occurs along with the stress application. The phase shifts were measured for the discrete reflection echoes that traveled long distances (top-to-bottom echo and multiple echoes in the head of the rail). The compressive axial load was raised up to 60 tons with the Shinkansen (bullet train) rail samples, which exceeds the buckling load of long rails. Both techniques showed a linear response to stress with a sufficient sensitivity and robustness, which promise the development of a practical railroad maintenance technology. The effects of the liftoff and the residual stress distribution are determined.

Dynamic Interaction between Wheel and Track - A Parametric Search towards an Optimal Design of Rail Structures

SUMMARY The dynamic vertical interaction between a moving rigid wheel and a flexible railway track is investigated. A round and smooth wheel tread and an initially straight and noncorrugated rail surface are assumed in the present optimization study. A symmetric linear three-dimensional beam structure model of a finite portion of the track is suggested including rail, pads, sleepers and ballast with spatially nonproportional damping. The full interaction problem is numerically solved by use of an extended state-space vector approach in conjunction with a complex modal superposition for the track. Transient bending stresses in sleepers and rail are calculated. The influence of seven selected track parameters on the dynamic behaviour of the track is investigated. A two-level fractional factorial design method is used in the search for a combination of numerical levels of these parameters making the maximum bending stresses a minimum.

Ultrasonic measurement of thermal stresses in continuously welded rails

The paper presents an application of ultrasonic techniques for monitoring thermal stresses in continuously welded rail. Such stresses, when compressive, can lead to dangerous track buckling. The paper describes a probe-head which generates subsurface and reflected longitudinal ultrasonic waves propagating along the rail head. Results are presented of the measurement of acousto-elastic constants. The influence of rail and probe-head temperatures on stress readings is discussed. Results of field measurements of thermal stresses in rails in track are presented, showing the distribution of stresses along the 400 m track section.

A finite element and fatigue threshold study of shelling in heavy haul rails

A finite element study has been made of subsurface rail-wheel contact stresses in a heavy haul railway rail, and the near-threshold fatigue behaviour investigated for both standard carbon and head-hardened rail steels under mode II and mode III shear-loading conditions. Small, semielliptical regions of shear mode growth were found in the mode III tests and are thought to be equivalent to shell cracks. Mode I branch cracks arising from these are similarly believed to correspond to the generation of a transverse defect. Gauge corner shear stresses from the finite element analysis are used together with threshold stress intensity factor ranges from the fatigue tests on standard carbon rail in a fracture mechanics model of the transition from a shell to a transverse defect. When the effects of crack face friction and residual stress in the rail head are incorporated into the model, excellent agreement is obtained between the predicted size of a shell and that found from fractographic examinations of failed rail samples.