Peter Mutton

On Constitutive Models for Ratcheting of a High Strength Rail Steel

The ratcheting behaviour of a hypereutectoid high strength rail steel with carbon content of 0.85% was experimentally studied under both uniaxial and bi-axial cyclic loadings recently by the authors. To numerically simulate the multiaxial ratcheting behaviour of the rail steel, the Abaqus built-in Lemaitre-Chaboche model was applied first in current study. Following Abaqus documentation, the material data for the Lemaitre-Chaboche model were calibrated from the uniaxial loading test results. Comparing with experimental data, the Lemaitre-Chaboche model with the calibrated data provides overpredictions for the ratcheting responses of the rail steel under both uniaxial and bi-axial loadings. After that, a modified cyclic plasticity model with a coupling multiaxial parameter in the isotropic and kinematic hardening rules was applied for the material. The material data for this modified model were calibrated from both uniaxial and bi-axial loading tests. Comparison between the simulated results and the experimental data show that this modified cyclic plasticity model has the capacity to simulate both uniaxial and multiaxial ratcheting behaviour of the hypereutectoid rail steel with an acceptable accuracy.

The effect of geometric features on multi-axial fatigue behaviour of aluminothermic rail welds

Aluminothermic rail welds typically exhibit a variable and often inferior performance when compared with flash butt welds. Fatigue failure as a result of surface defects or harsh geometric features in the presence of high axle loads and tractive forces gives rise to the so-called straight break and horizontal split web fractures. In this study, the reduction of fatigue performance due to geometric irregularities is investigated using a multi-axial high cycle fatigue criterion based on the critical plane concept. A thermo-structural finite element model of a track containing an aluminothermic weld is linked with a developed computer code to perform fatigue crack initiation analysis. Two geometrically different aluminothermic welds, one of which is widely used in Australian heavy haul railways, are investigated in terms of fatigue probability, to facilitate a better insight into the effect of weld collar shape and geometry at the edge of the weld collar on fatigue behaviour. The results confirm that the amount of fatigue damage is critically dependent on the geometric features of the collar edge, especially at the underhead radius which undergoes severe fatigue loading under some operational conditions.

Measurement of Residual Stresses in Aluminothermic Rail Welds Using Neutron Diffraction Technique

It is understood that residual stresses in aluminothermic rail welds play an important role in the fatigue behaviour of the welds. Measuring the residual stresses in the critical areas and finding the correlation between these stresses and welding parameters can be useful in order to alter the welding procedure and improve the fatigue performance of these welds. In this paper, residual stresses in the foot of the rail weld were measured using neutron diffraction and the preliminary results are presented.

On the Evaluation of the Stress State in Rail Head for Assessing Fatigue Resistance

To search for a single parameter to evaluate the stress state in rail head during wheel/rail rolling contact situations, the stress-based and the strain based phenomenological approaches for multiaxial fatigue analysis can be considered as the candidates. Following the stress-based approach, the maximum von Mises stress range can be applied as a single parameter to evaluate the stress state in the rail head. However, the von Mises stress range only relies on the stress field in the rail head for the fatigue analysis, which is not sufficient for assessing the fatigue resistance of the rail steel. The Smith-Watson-Topper (SWT) method, the strain-based phenomenological approach for multiaxial fatigue analysis which considers stress, elastic strain and plastic strain components, is then adopted to study rolling contact fatigue in the rail head. Combining with the three-dimensional finite element modelling of a steady-state wheel/rail rolling contact, the numerical procedure to calculate the SWT parameter in the rail head is presented. The capability of the SWT method to predict the initiation of fatigue cracks in the rail head is confirmed in a case study. Consequently, the maximum SWT parameter is proposed as a single parameter to effectively evaluate the stress state in the rail head.

Classification of Impact Signals from Insulated Rail Joints Using Spectral Analysis

Insulated Rail Joints (IRJs) are a railway track component that generates impact noise and requires close maintenance. Instrumented Revenue Vehicles (IRVs) developed by the Institute of Railway Technology at Monash University measure the interaction between the vehicle and track. Impact signals were measured and post-processed from vibration sensors located on the side-frame at IRJ locations. Wavelet analysis was used to interrogate the non-stationary impact signals. Wavelet energy was used as the wavelet feature extraction techniques in the frequency domain. The wavelet energy impact signatures were clustered using multi-signal discrete wavelet transform clustering. These clusters classified the empty and loaded conditions of the wagon from the vibration response. Frequency identifications were created from the clustering and the severity of the impacts in the frequency domain could be determined from the cluster numbers.

Laser Cladding for Railway Repair: Influence of Depositing Materials and Heat Treatment on Microstructural Characteristics

The contact between train wheels and rail tracks is known to induce material degradation in the form of wear, and rolling contact fatigue in the railhead. Laser cladding, a state of the art surface engineering technique, is a promising solution to repair damaged railheads so as to alleviate the rates of degradation and extend the component longevity. In this paper, effects of cladding material and heat treatment on microstructures of laser treated rails is presented. Laser cladding of premium hypereutectoid rail, four different depositing materials, and different heat treatments were investigated. For the preheating length of 400 mm, equal to the cladding length, the formation of martensite in heat affected zone (HAZ) was not hindered by the application of preheating to 350 °C on the rail-longitudinally deposited railhead of the four materials. Consequentially, cracking in the clad and HAZ was expected. An uncracked microstructure with excellent microstructural consistency across the entire rail-longitudinally deposited railhead and its HAZ was established using a heat treatment combination consisting of pre-heating, postheating, and slow cooling, regardless of the depositing materials.

Effect of head wear and lateral forces on underhead radius crack propagation

This paper investigated the effect of rail head wear (HW) and lateral forces on underhead radius stress conditions and resulting stress intensity factors (SIFs) of a long transverse crack. The occurrence of tension spikes at the underhead radius of the rail as a result of localised vertical and lateral bending of the head-on-web was significantly exacerbated with increasing rail HW. The extended finite element method (X-FEM) modelling, which had previously been validated by comparison with in-track measurements to verify the prediction of tension spikes, was used to model a single rail on discrete elastic foundations. SIFs along the crack front were parametrically evaluated in terms of changes in the contact patch offset (CPO), the (L/V) ratio of lateral (L) to vertical (V) loads, the rail HW, and crack size and shape. The X-FEM results revealed that for a long transverse crack, extending the crack length to the underhead radius position results in higher SIFs across the underhead radius as a result of tensile bending stresses. These higher SIFs can contribute to a massively higher crack growth rate at this location, as was evidenced by the crack growth morphology at the underhead radius.

Fatigue in Railway Components - Understanding vs. Resolution

The consequences of surface finish and decarburization on the fatigue performance of cast and forged steel components in the railway industry is substantial, and means that fatigue cracking is an ongoing issue across the industry. Examples of loading spectra for coupler forces and track loads are presented, along with data from past investigations showing the severe penalty in terms of fatigue life caused by inadequate surface finish at critical locations of components under fatigue loads. Managers in railway industry need to understand the technical case for increased manufacturing requirements, as costs from operational losses may well have made the economic case for increased requirements more compelling. Various options for improving the surface finish at critical locations that are prone to fatigue are available, and should be explored to reduce the vulnerability of these components to failure via fatigue cracking.

Fatigue Analysis of the Rail Underhead Radius under High Axle Load Conditions

An evaluation of the potential risk of fatigue damage at the rail underhead radius (UHR) due to the occurrence of a short duration tensile stress peak, as a wheel passes over, has been examined. The tensile stress peak is mainly due to the localised bending of the rail head-on-web and its magnitude is associated with the contact position, lateral and vertical forces and rail head wear (HW). The stresses at the underhead radius have been explored using the finite element method (FEM). The Dang Van (DV) criterion, implemented as a customised computer programme, was used to identify the fatigue damage at the UHR. Fatigue behaviour under heavy haul conditions was compared for heat-treated low alloy, euctectoid and hypereutectoid rail grades in order to predict allowable rail head wear limits.

Modifying residual stress levels in rail flash-butt welds using localised rapid post-weld heat treatment and accelerated cooling

AbstractFlash-butt welding is used in the manufacture of continuously-welded rails. Finished welds typically exhibit high tensile residual stresses in the rail web and at the upper surface of the rail foot, which may increase the risk of fatigue failure in service. An understanding of the influence of the welding process, including post-weld cooling, on the residual stress distribution is necessary to improve the performance of flash-butt welds by post-weld heat treatment (PWHT), since incorrect treatment may have adverse effects on both residual stress and weld material characteristics. A finite element model has been developed to simulate post-weld cooling in flash-butt welded AS60 kg m–1 rail. Computed thermal histories for normal (air) cooling, rapid PWHT, and accelerated cooling (water spray) were used as inputs to calculate sequentially coupled stress–time histories, including phase transformations. In addition, the localised influence of the initiation time for rapid PWHT, after final upset, on the...