This research extends the application of an Arbitrary Lagrangian-Eulerian (ALE)-based finite element simulation model specifically designed to analyze high-speed milling processes in rail milling, emphasizing the dynamics of chip formation and the stress and temperature distributions within the milled workpiece. The study primarily investigates milling operations at two cutting speeds: 240 m/min, where results are validated against experimental data, and 380 m/min, which offers new insights into the material behavior under high-speed milling conditions. The evaluation critically assesses the capability of the model in predicting material flow, residual stress fields and heat distribution, aligning these predictions with experimental observations. The findings demonstrate the robustness of the numerical model in simulating complex physical phenomena specific to high-speed milling.

Twin disc tests are performed to determine the wear behaviour of three advanced crossing materials. In particular, the austenitic Hadfield steel Mn13, the ultrafine-pearlitic R400HT and the chromium bainitic CrB1400 steels are benchmarked. The investigated crossing materials are combined with the standard wheel material ER7. The tests are performed under two different contact pressures, 1400 and 1 800 MPa, respectively. Dry conditions and a slip of 0.5% are used. The parameters evaluated are: wear rates, wear debris, plastic deformation, microstructural changes, friction coefficient and material hardness. R400HT is identified as exhibiting the highest wear resistance, although CrB1400 shows comparable results. Mn13 exhibits the highest wear rates. Three primary reasons for the elevated wear rates of Mn13 are identified. These include a significantly lower initial hardness, a distinct hardening mechanism in conjunction with a high work-hardening potential and a different wear mechanism that shows a high dependence on the applied contact pressure. The different wear mechanism is expected to be the main driver for the high wear rates.

The growing demand for railway transportation requires higher speeds and axle loads, but this can negatively impact critical track components like railway crossings. This study investigates the dynamic behavior of high-speed turnout components under varying train speeds and axle loads, focusing on vertical displacements and contact forces. Using detailed finite element analysis, comparative results reveal trends in rail displacements, with higher speeds reducing the responsiveness of the crossing tip (frog) to rapid changes. The study also highlights the role of static axle loads in maintaining wheel-rail contact and identifies vulnerable components, such as the frog tip and base plate, under higher static loads. These findings provide valuable insights into the dynamics of turnout components, enabling stakeholders to derive strategies for improving turnout performance and safety.

This study presents an efficient 3D finite element modeling approach for simulating cyclic elasto-plastic Hertzian contact of crossed cylinders. The research focuses on understanding rolling contact fatigue influences and cyclic plastic deformation in wheel-rail interactions. A newly developed simulation framework extends an existing Abaqus rollover plugin to enable large-scale parametric studies by improving computational efficiency while maintaining accuracy. The framework is validated against Hertzian contact theory and applied to evaluate elastic/plastic shakedown and ratcheting. The findings provide insights into the stress redistribution and plastic strain accumulation in the subsurface regions, demonstrating the model's capability for predicting material degradation. This work contributes to the optimization of railway component designs and maintenance strategies through enhanced predictive modeling.

In this work a detailed metallographic analysis of squats is performed and assessed. The used rail samples with squats are taken from tracks of the Swiss Federal Railway (SBB). They involve different rail materials, track layouts as well as squats at various stages of their evolution. Consequently, early stage "mini" squats are examined. A fully-developed squat is opened along the crack face and several squats are sectioned in longitudinal or transversal direction. The sectioned cracks substantially help to understand the mechanism squat by creating a reconstruction of a squat below the rail surface. Furthermore, the residual stresses of one rail sample are analysed. The variety of investigations enables to obtain a detailed picture of squats and helps to find their root cause.

As train passengers, we value the environmental friendliness of the railroad, and it is important to us to arrive at our destination safely and on time. However, this is only possible if all technical components in the rail system work reliably and necessary inspection and maintenance can be planned efficiently. The expansion of high-speed tracks and the ever tighter travel cycles naturally also increase the material-specific requirements for safety-relevant railroad components. This in turn requires an in-depth understanding of the functionality and service life of rail vehicle and rail infrastructure components as well as the use of modern materials in order to meet the high demands. There is consequently still a great need for research in the rail sector. The challenge railroad operators are facing is to become even faster, more comfortable, more punctual, and more environmentally friendly, but to still remain economically viable. In order to reconcile the safety and punctuality (availability) characteristics initially mentioned and to increase the economic efficiency by means of extended maintenance intervals, the current status of safety-relevant railroad components must be known. This is why these components are monitored and the corresponding measurement data are logged and evaluated. Based on such condition monitoring systems, customized maintenance measures can be planned timely and carried out at the best possible time slots. Railway-related research activities at the MCL deal precisely with these topics of condition monitoring and the resulting maintenance of rail infrastructure (rails and switches) and railway wheelsets (wheels and wheelset axles).

High-speed turnouts are the key components of high-speed railways. The crossing panel in the turnout is one of the critical zones where high loads occur when the train passes through. To reduce the dynamic forces during high speed or heavy haul trains passing, swing nose crossing designs are used. For those swing nose crossings, a drive and locking unit is used for positioning the crossing nose for the correct driving direction and to keep the crossing nose safely in position. To guarantee the correct position a detection unit is integrated into such a drive and lock unit. The focus of this paper is on the numerical simulation of the detailed swing-nose crossing together with drive locking and detection (DLD) devices and their behavior during high-speed operation. For this purpose, a dynamic model based on the Finite Element Method (FEM) is presented that enables to investigate the deflections and stresses in the turnout components as well as the dynamic behavior of the DLD system and its influence on other components during wheel passage.

Squats are rather complex failure mechanisms in rails and challenge railway operators all over the world, thus calling for a detailed investigation of squats by means of finite element analysis to locate the initiation and propagating mechanisms. In this work, a cyclic three-dimensional (3D) finite element model of a wheel-rail contact including an initial penny-shaped defect is used. This work presents the implementation of the starting penny-shaped crack in the rail for a wheel-rail simulation by utilising a submodel strategy. Moreover, viable evaluation options are shown. In the future, this set-up will help to assess multiple crack positions and possible squat growth mechanisms.

This paper presents a whole system model framework that enables a holistic prediction of accumulated track damage in railway turnouts. A modular approach allows for insight into the interaction of different damage mechanisms such as rail profile change due to the plastic deformation and wear as well as track settlement. The methodology focuses on the two most critical areas of the turnout in terms of damage: switch and crossing panels. It is shown that at the beginning of the service life of the turnout the running surface of the rails in these areas change significantly due to plastic deformation, which in turn increases the dynamic impact forces from passing vehicles. These impact forces cause vertical track settlement that is most pronounced in the crossing area. Track settlement introduces additional dynamics into the system leading to self-reinforcing behaviour. It is shown that the proposed methodology can predict accumulated track damage accounting for the coupling between different damage modes such as track settlement, rail profiles plastic deformation and wear. It can therefore be used for holistic assessment of turnouts e.g. in design optimisation studies.

The residual stress state of rails is a key influencing factor which promotes the initiation and propagation of squats. Squats are widely spread rail surface defects, which pose a significant problem all around the world. Therefore, a Finite Element (FE) simulation of a new rail has been conducted to calculate the residual stresses after 100 rollover cycles. In order to validate the FE results two different residual stress measurement approaches for rails with and without squats have been evaluated within this work. The first measurement, the contour method, determines the longitudinal residual stresses of the whole rail cross-section. The second measurement method, X-ray diffraction, provides a stress profile for a specified depth. By investigating the residual stress state of rails, the set-up of a realistic 3D rollover simulation including squats will be facilitated in future works.

To tackle the problem of various types of rail damage, such as rolling contact fatigue (RCF) or wear, a profound knowledge of the occurring mechanisms is necessary. This paper presents a newly developed full-scale test rig experiment that involves inserting softer pins into the rail head. These tests help deepen our understanding of shear deformation in rail steels. Furthermore, a finite element (FE) simulation approach is introduced that can be related to the test rig experiments. With these experiments, in combination with the FE simulation, valuable information regarding the plastic deformation can be obtained. This methodology allows predictions regarding a rail's material behaviour during cyclic wheel loading. Moreover, it enables an effective and rapid qualitative material assessment, reducing the costs of expensive and time-consuming experiments.

A dynamic 3D finite element model for the calculation of profile degradation in the switch panel is presented. The model includes the contact between wheel and rail, as well as the contact between switch rail and stock rail to allow an elastic relative movement between the two rails. Break-outs of the switch rail tip can be facilitated by this relative movement and the stresses and strains at this interface are calculated. The profile degradation of the switch rail due to contact loading between wheel flange and switch rail is numerically simulated considering the cyclic plastic deformation of the rail material. The sliding wear is evaluated separately and superimposed to the geometrical change caused by the plastic deformation.

The crack path under cyclic Mode-II loading in undeformed and pre-deformed pearlitic rail steel R260 is investigated. To produce large-scale specimens with pre-deformed microstructures two methods are applied. Firstly, cylinder bars are processed using an axial-torsion machine resulting in a moderate deformation. Secondly, a new high pressure torsion (HPT) setup is developed to achieve a more strongly deformed microstructure. In the fatigue tests, a distinctive change in the crack path is observed. In the undeformed and moderate deformed specimens, the cracks bifurcate and turn into a Mode-I dominated mixed-mode. In the HPT material, the cracks grow in Mode-II without mixed-mode propagation. For rolling contact fatigue cracks in rails these experimental results indicate a strong connection between the propagation mode and the anisotropy of the highly deformed pearlitic microstructure. This microstructure is characteristic near the wheel-rail contact surface. In future, these findings are important to improve numerical-based crack growth prediction models.

A numerical tool is proposed to simultaneously assess various damage mechanisms that are driven by contact loading. The tool transfers loads to the contact-patch level using three contact parameters: the maximum contact pressure (pmax), the creepage (c) and the contact length (2a). The local wear and RCF predictions are implemented based on existing models from the literature. The load input can originate from numerical vehicle–track simulations or manual input of the user. The assessment tool is applied for a finite element analysis of a fixed manganese crossing nose to prove its validity. The algorithm is implemented via an automated Python code, which, on the one hand enables damage prediction for track components based on standard damage models. On the other hand, knowledge of novel local contact damage models can be transferred to the scale of track components.

Observations in a railway track frequently show the start of a squat-form crack right next to the wheel-rail running band on the rail head surface. This article investigates the potential of a head check-like surface defect near the running band to initiate a squat formation. Cross sectioning of the rail samples having squats in the initial stage of development suggested the crack initiation in a transverse plane (perpendicular to the rail traffic direction), implying that broadening to a typical squat shape in the longitudinal direction (rail traffic direction) occurs afterwards. The influence of possible factors that might trigger the squat formation particularly on the transverse plane across the rail is elaborated in the numerical study. The tendency of one defect to grow rather than another is analysed by configurational force theory in order to determine both the crack driving force value and the crack growth direction. The effect of the contact patch variations and changed frictional properties at the crack faces on the squat-like crack development are studied in detail. The numerical results show that analysed cracks are able to grow under particular wheel loading in the directions that are in accordance with observed squat growth. These results suggest lateral forces as one of the main suspected determinants favouring the squat initiation.

A new non-standard experiment is developed to measure fatigue crack propagation in the shear crack growth mechanism occurring in rail and crossing parts. Pre-cracked tubular specimens are loaded under cyclic Mode-II and static compressive Mode-I stresses to reproduce those shear crack growth conditions. To investigate the influence of severe plastic deformation as found in the top of rails in track, specimens are pre-deformed using high pressure torsion. For the pearlitic rail steel, the crack path and crack growth behavior changes distinctively with material pre-deformation: In the undeformed material cracks bifurcate under the Mode-II loading and turn into a Mode-I dominated mixed-mode. After severe plastic deformation, the crack propagates in Mode-II at significantly lower load levels without bifurcating. A detailed analysis of the fracture surfaces as well as the correlation of the crack path and microstructural alignment confirm these findings. Therefore, the proposed experimental procedure could provide Mode-II fatigue crack growth data required to predict crack propagation within rolling contact fatigue in rails and crossings.

Within this work, the thermal stress build-up of chemically vapor deposited TiCN/alpha-Al2O3 bilayer coatings was controlled by tuning the coefficient of thermal expansion (CTE) of the substrate material. This was implemented through a Co content variation from 6 to 15 wt.% in WC-Co substrates, which exhibit higher CTEs with increasing Co contents and thereby approach the GTE values of TiCN and alpha-Al2O3. High temperature X-ray diffraction was employed to determine thermal expansion of an alpha-Al(2)O(3 )powder. Crystallographic texture of the alpha-Al2O3 coating layer was evaluated by electron backscatter diffraction and taken into consideration in order to assign the appropriate in-plane CTE. This consideration indicated a lower CTE mismatch of alpha-Al2O3 with WC-Co, compared to TiCN with WC-Co. X-ray diffraction was further utilized for the determination of residual stress in TiCN and alpha-Al2O3, demonstrating a decrease in both layers for Co contents below 12.5 wt.%. Decreasing stress signaled the formation of thermal crack networks confirmed by scanning electron microscopy surface images. Lower residual stresses were determined in TiCN compared to alpha-Al2O3 layers of bilayer coatings, contradicting finite element simulations of thermo-elastic stress, that were carried out to illustrate the stress relaxation effects caused by thermal cracks. Monolayer TiCN coatings were annealed at 1000 degrees C, to replicate stress relaxation taking place during alpha-Al2O3 deposition, exhibiting a similar residual stress state to TiCN base layers of bilayer coatings. Thermal crack formation was found to be the dominating stress relaxation mechanism in alpha-Al2O3, while TiCN undergoes further relaxation through secondary mechanisms.

In service, milling tools have to cope with severe levels of thermal and mechanical load. Especially temperature influences the damage behavior of a tool’s cutting edge by influencing material properties and thermally induced stresses. It is therefore of relevance to gain quantitative information on the thermal tool load situation. Information on temperatures in milling tools is not readily available today. Therefore, extensive experimental effort was necessary to determine temperatures in-situ during milling in the axial center of a rotating end mill and in a Ti6Al4V workpiece near the milled surface. The used end mill was a WC-Co hard metal tool protected by a TiAlN coating. Since the damage-relevant cutting edge temperature is not directly accessible by experimental means, a simulation was employed. The transient temperature field in the tool was calculated by an iterative and synergetic use of two-dimensional finite element cutting models, three-dimensional finite element end mill models and two-dimensional workpiece models. The simulation allows for the description of the time-dependent temperature distribution from the chip formation site at the cutting edge to the axial tool center and into the workpiece, where thermocouples were placed in experiments. Validation of the calculated cutting edge temperatures was performed for 5000 individual consecutive cuts via comparison of results for tool core temperature in experiment and simulation. The model yields a very pronounced concentration of the thermal load maximum of T>650 °C near the cutting edges in a very small volume of only 1 ppm of the tool’s volume. In particular, the model’s spatial discretization is able to resolve the gradient of temperature in the hard coating towards the coating/substrate interface, showing temperature shielding effects of the hard coating.

TiCN coatings were grown by chemical vapor deposition (CVD) on WC-Co substrates with different Co contents, in order to control thermal stress. The driving force for the development of thermal stress is attributed to the difference between room and deposition temperature (Delta T approximate to -780 degrees C), and the mismatch of the coefficient of thermal expansion (CTE) between substrate and coating. Co contents of 6, 7.5, 10, 12.5, and 15 wt% were utilized to adjust the CTE of the substrate, and therefore tune the stress in TiCN coatings. Dilatometry of the substrates and high temperature X-ray diffraction of a powdered TiCN coating indicate a decreasing CTE-mismatch for increasing substrate Co contents. In consequence, residual stress in TiCN determined by X-ray diffraction increases up to 662 +/- 8 MPa with decreasing Co contents down to 10 wt%. For Co contents below 10 wt %, the residual stress decreases. The formation of thermal crack networks in TiCN, analyzed by scanning electron microscopy, coincides with 10 wt% Co. Stress relaxation in TiCN coatings through the formation of thermal cracks becomes evident. A finite element simulation utilized for the calculation of residual stress distributions reveals shielding effects, which occur with the introduction of thermal cracks. Discrepancies between experimental and simulated thermo-elastic stresses imply the presence of secondary relaxation sources. High temperature residual stresses in TiCN, determined up to 1000 degrees C (i.e. above deposition temperature), suggest additional thermal crack formation for substrate Co contents of 6 wt%.