Improvement of the rail milling process & Evaluation of its potential for the reduction of rail defects

Research output: ThesisDoctoral Thesis

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Abstract

In this thesis, the maintenance process “rail milling” in general, the rolling-sliding contact behavior of milled rails in service, and the residual crack growth behavior in maintained rails are analyzed numerically and validated experimentally. The rail milling process is simulated using both three-dimensional and two-dimensional models. The three-dimensional simulation is set-up with DEFORM 3D and provides a general picture of the whole milling process concerning the rail profile change and the chip formation. The milling process is investigated in greater detail in a two-dimensional numerical analysis using ABAQUS/Explicit and an Arbitrary-Lagrangian-Eulerian method. A new model is presented as state of the art approaches are not able to calculate the milling force, the temperature, and residual stress fields in the milled workpiece (rail) accurately and numerically efficient. A central feature of the new model is the representation of nearly the whole chip production including a realistic description of the changing uncut chip thickness during one chip removal step. The chip shape, as well as the temperature exposure and the residual stress field of the milled rail compare well with measurements. Using the finite-element software ABAQUS/Standard a three-dimensional and a two-dimensional rolling-sliding wheel-rail contact simulation are set up to investigate the in-service behavior of milled rails. This part of the thesis focuses on the change of the surface roughness and the development of the residual stress field after cyclic rolling-sliding contact. The obtained numerical results are compared to experimental investigations of milled and traffic loaded rails that are taken out of track after specific loading scenarios. The change of the surface roughness and residual stresses are measured. They show a good agreement with the simulation results. The microstructure of the investigated pearlitic rails is metallographically characterized before milling, after milling and after being subjected to specific loads in track following milling. By means of optical microscopy, scanning electron microscopy and transmission electron microscopy, it is shown that the milling process deforms the rail material 8 µm into the depth by shearing. The shear strain increases toward the rail surface. The rails are loaded after milling by light traffic which changes the microstructure, i.e. the influence of rolling-sliding contact becomes visible, and the signs of wear and shear deformation are shown. In the last part of this thesis, the influence of rail milling on residual crack growth and crack propagation in track is studied. The experimental results of the track tests indicate the beneficial effects of milling on residual crack growth. It is shown that only the typical rolling-sliding wheel-rail contact influences the residual crack growth whereas the milling influence can be neglected.

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Translated title of the contributionVerbesserung des Schienenfräsprozesses & Bewertung seines Potentials auf die Reduktion von Schienenschäden
Original languageEnglish
QualificationDr.mont.
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Publication statusPublished - 2019