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Sandstrom J.,Chalmers University of Technology | Sandstrom J.,Epsilon Utvecklingscentrum Vast AB
International Journal of Fatigue

A numerical model for predicting the probability of subsurface initiated rolling contact fatigue failure in railway wheels subjected to operational loading is presented. The loading is evaluated through simulations of dynamic train-track interaction incorporating the influence of, e.g., corrugation. Contact stresses are found from Hertzian theory and the resulting stress field from theory of elasticity. Fatigue damage is evaluated by use of a Wöhler curve where the fatigue strength is decreased due to the influence of material defects, which are presumed to be of random size and occurrence in the stressed volume of the wheel rim. Damage accumulation is performed using the Palmgren-Miner rule, extending the model to cases of variable loading. The results show how a combination of rail corrugation and high train speeds have a significant impact on the probability of fatigue failure. A sensitivity analysis reveals a strong influence of the fatigue strength and the material defect distribution on the probability of fatigue failure. © 2011 Elsevier Ltd. All rights reserved. Source

Christensen M.L.,University of Aalborg | Johansson C.,University of Aalborg | Johansson C.,Epsilon Utvecklingscentrum Vast AB | Sedin M.,Chalmers University of Technology | Keiding K.,Chalmers University of Technology
Powder Technology

For activated sludge, manure, dextran-MnO 2 particle suspensions, and other organic slurries, the filtrate volume increases nonlinearly with the square root of time (nonlinear filtration behavior). This study uses dextran-MnO 2 particles as a general model compound, and the observed behavior is discussed in relation to sedimentation, blinding, medium resistance, and dynamic cake compressibility. Only dynamic cake compressibility is able to explain the experimental data. The soft solvent-swollen dextran materials deformed at high pressure, filling the voids in the cake. This was a dynamic process: specific cake resistance increased with time, resulting in nonlinear filtration behavior. The dynamic cake compressibility implies that the equilibrium porosity in the cake is not reached instantly during filtration. Thus, the effect of time on porosity and resistance must be considered when dewatering organic materials. © 2010 Elsevier B.V. Source

Johansson A.,Chalmers University of Technology | Johansson A.,Epsilon Utvecklingscentrum Vast AB | Palsson B.,Chalmers University of Technology | Ekh M.,Chalmers University of Technology | And 5 more authors.

A methodology for the simulation of degradation of rail profiles in switches & crossings (S&C) is presented. The methodology includes: simulation of dynamic vehicle-track interaction considering stochastic variations in input data (such as wheel profile, train speed and wheel-rail friction coefficient), simulation of wheel-rail contacts accounting for non-linear material properties and plasticity, and simulation of wear and plastic deformation in the rail during the life of the S&C component. The methodology is demonstrated by predicting the damage of a switch rail profile, manufactured from R260 steel, when exposed to freight traffic in the diverging route (facing move). In particular, the consequences of increasing the axle load from 25. tonnes to 30. tonnes are studied. © 2010 Elsevier B.V. Source

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