Modelling of wear and crack initiation in rails / Gordana .

Abstract

The ‘Dynarat’ computer simulation of ratcheting wear and failure of rail steel has been developed at Newcastle University over the past decade based on laboratory tests and analysis of British normal grade (R220) rail steel. The aim of this thesis is to develop material models for Dynarat that can be used to predict wear and rail life for R260 rail steel, which is used widely in Europe and increasingly in Britain, and also for newer premium grade pearlitic rail steels. Laboratory twin-disc testing and metallurgical material analysis were used to obtain data for characterising and modelling material response to repeated loading. The relationship between material hardness and plastic shear strain is central to the material model used in the Dynarat simulation, and is determined for the materials tested here by studying the measured hardness and plastic strain. Additional calibration of the wear rate was achieved by performing Dynarat simulations that closely matched the laboratory tests. In addition to the material model development, the contact stress model used by Dynarat for modelling wheel-rail contact is improved. Previously the driving stress for plastic strain accumulation was the orthogonal shear stress in the plane of the simulation. In the new model, plastic strain accumulation is now made directional, with components in the x and y directions. Partial slip is now implemented in the 3D simulation, to approximate the real wheel-rail contact, with both contact region and adhesive zone modelled as ellipses. Two types of high-speed train at two curves on the UK’s East Coast Main Line have been simulated with the new computer model to study the effects of traffic mixtures. Wear rates and time until crack initiation are obtained. The new model provides a tool to help rail/wheel manufacturers to choose the best steel, and for maintenance personnel to predict rail wear and cracks, and thus to help plan grinding schedules in order to optimise rail life and safety.