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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 98
Edited by: J. Pombo
Paper 95

The Suitability of Using Accumulated Plastic Strain to Assess the Damage at the Rail-Wheel Interfaces

I.U. Wickramasinghe1,2, D. Hargreaves1 and D. De Pellegrin1

1School of Chemistry, Physics and Mechanical Engineering, Faculty of Science and Technology, Queensland University of Technology, Brisbane, Australia
2Cooperative Research Centre (CRC) for Rail Innovation, Australia

Full Bibliographic Reference for this paper
I.U. Wickramasinghe, D. Hargreaves, D. De Pellegrin, "The Suitability of Using Accumulated Plastic Strain to Assess the Damage at the Rail-Wheel Interfaces", in J. Pombo, (Editor), "Proceedings of the First International Conference on Railway Technology: Research, Development and Maintenance", Civil-Comp Press, Stirlingshire, UK, Paper 95, 2012. doi:10.4203/ccp.98.95
Keywords: plastic equivalent strain, finite element modelling, wheel-rail contact, pressure load, material plasticity, Abaqus simulations, Hertzian contact theory.

Numerous finite element analyses have been carried out using various plasticity models to investigate the effect of friction force on the rail head in relation to both the development of the accumulated plastic strain (PEEQ) and the changes in the depth of the PEEQ distribution in the wheel-rail contact. The normal force distribution on the rail head has been assumed to be Hertzian. The tangential force was implemented as a fraction of the normal force. Each analysis was carried out for a single pass and the effect of various friction coefficient values has been observed. The study presented in this paper focuses on the suitability of using the plastic equivalent strain to study the rail wear. The study compares the depth of the maximum PEEQ and the maximum von Mises stress and conclusions are made based on the outcomes obtained.

The elastic behaviour of the wheel-rail contact is described using Hertzian contact theory [1]. The development of the pressure loaded rail model closely follows the work done by Ringsberg et al. [2]. The present rail model, developed for the analysis, is 80 mm long. The model is divided into two parts, i.e. a bottom part and inner top part. An elastic-plastic material model defines the materials in the rail top part, since this is the volume within which plastic deformation is likely to occur as a result of the wheel-rail rolling contact. The outer part represents the elastic surroundings of the rail, where only elastic deformation occurs, and is of less interest in the current investigation. The distributions of contact load and traction load from the wheel-rail contact are applied to the centre of the rail top part by using Abaqus subroutines DLOAD and UTRACLOAD. Material models are described by constitutive equations governing the stress or the strain response for a material for a given stress or strain history. In this study, the nonlinear isotropic-kinematic cyclic hardening model in Abaqus was used to define classical metal plasticity. Five parameters were from the previous studies considered in the study. The axle load of 14 tonnes, corresponding to a rail normal force of 70000N, was used for the current investigation of all four models.

Based on the models analysed and the results, it is concluded that at lower traction levels with higher vertical loads, the maximum PEEQ is generated at a higher depth below the surface than to the maximum von Mises stress. And at the zero friction coefficient level maximum PEEQ is at 1.9mm below the surface and maximum von Mises stress at 0.3mm below the surface. At the 0.3 friction coefficient maximum PEEQ reaching the surface in all analysed material models where it is gradually decreased along the rail cross section. So the study concludes that PEEQ is a better parameter to study the rail wear using plastic material models. This phenomenon can be used with previously developed ratchetting theory to predict the rail life.

H. Hertz, et al., Miscellaneous papers, Macmillan, 1896.
J. Ringsberg, H. Bjarnehed, A. Johansson, B.L. Josefson, "Rolling contact fatigue of rails-finite element modelling of residual stresses, strains and crack initiation", Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 214, 7-19, 2000. doi:10.1243/0954409001531207

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