Contribution à l'étude du comportement mécanique de voies ferrées, composants à caractère dissipatif non-linéaire : semelle sous rail et sous-couche de grave bitumineuse.

Abstract : Repetitive dynamic loads caused by passing trains can damage a railway track, especially at high speeds. The complex multilayer structure of the modern track consists of: stainless steel rails, elastomeric rail pads, concrete sleepers, track ballast and sub-ballast layers. Investigation of the mechanical behaviour of the railway track structure (as the whole and by parts) can have a great importance for the improvement of safety and efficiency of railway transportation.In the present study rail pad and bituminous mixture (BM) sub-ballast layers of a standard ballasted railway track were considered for investigation. These parts of the track were chosen for their similarities in the mechanical behaviour (nonlinearity and energy dissipation) and function (reduction of the dynamic part of load, an influence on the load distribution).The first chapter reviews the main aspects of the mechanical behaviour of elastomeric materials and covers the common theoretical approaches, appropriate for the modelling of this behaviour. The Convolution Integral approach (CI-model) was chosen to represent the mechanical behaviour of a rail pad material as a natural extension of theory of linear viscoelasticity, based on extension of the well-established Boltzmann Superposition Principle.The second chapter is devoted to study of elastomeric material of a rail pad and to numerical modelling of a whole elastomeric rail pad structure subjected to common track loads. Special attention was given to possibility of the model to describe the nonlinearity of the mechanical behaviour and capability of energy dissipation.Sufficient conformity between experimental and numerical results was established on loading part of a Force vs Displacement curve (an error of 1 % was obtained for the stiffness value) for the quasi-static loading, while prediction of the residual compression displacement remains poor, especially in the first loading cycle (2.2% of the macroscopic strain against 0.4% in experiment). The observed discrepancy led to poor prediction of the dissipated energy (an error of 37.5 % was found). Comparison between results of the numerical simulation and in situ experimental measurements has shown that the FE model is capable to describe dynamic behaviour of a rail pad structure to within the error of prediction of the residual compression displacement.Possible ways to simplify the numerical model, discussed in the second chapter, generally lead to high overestimation (2D plain strain and 3D grooveless models) or underestimation (2D plain stress model) of the rail pad mechanical behaviour.The third chapter of the thesis is connected to the study of a BM material, used on a railway track as a sub-ballast layer. Influence of size and volume fraction of monodisperse spherical inclusions, randomly packed into a cubic matrix, on the mechanical behaviour of obtained composite structure were investigated using “Virtual Material” approach. This approach allows numerical study of a theoretical case without losing connection with a real experiment (by means of direct geometrical correspondence). Parameters of 7 specimens were chosen in accordance with Doehlert experimental design.Analysis of “response surfaces” has shown that both F_max and E_% have a strong dependence on the value of V_fr and almost no dependence on the value of D.Stress/strain concentrations were analyzed using FE method on example of V0225-D08 specimen. This allows to find and to visualize load-bearing chains going through the matrix. Von Mises stress in load-bearing chains is almost 8 times higher than the average in the matrix.More complex models (real and numerical) in terms of problem discretization (more than one inclusions’ fraction, different inclusions’ shapes, etc.) can be developed and studied in the similar way. Moreover, the recent progress in additive manufacturing technologies shows potential to create complex heterogeneous specimens with an increased precision.
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Roman Zhuravlev. Contribution à l'étude du comportement mécanique de voies ferrées, composants à caractère dissipatif non-linéaire : semelle sous rail et sous-couche de grave bitumineuse.. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2017. Français. ⟨NNT : 2017ENAM0039⟩. ⟨tel-01744302⟩

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