Post Hatfield rolling contact fatigue: the effect of residual stress on contact stress driven crack growth in rail: combination of bending and contact stresses

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Rolling contact fatigue | Fletcher, D. I. | Report

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Title: Post Hatfield rolling contact fatigue: the effect of residual stress on contact stress driven crack growth in rail: combination of bending and contact stresses
Author(s): Fletcher, D. I.; Kapoor, A.
Abstract: This report continues from previous reports (1, 2, 3, 4) detailing the development of crack growth models for investigating the effect of residual stress and continuously welded rail stress on running surface initiated cracks in railway rail. This report focuses on assessing the combined effect of bending and contact stresses at short crack lengths, for which previous work has considered only contact and residual stresses. A combined model including both contact and longitudinal bending stresses has been developed. Bending stresses from previous work within the project form an input to this model, although bending stress data from other sources can also be used. Successful validation of the new crack growth model was carried out using input data from a standard beam bending solution and previous three-dimensional modelling of a cracked rail head. Further runs were carried out using data from the HSL bending model as input, and these are discussed below. While this is the best model of rail bending currently available within the project, some inconsistencies in the bending model where identified. In particular, the bending model predicts a non-symmetric pattern of rail deformation despite symmetric loading, and the sleeper supports included do not capture the behaviour of the rail-sleeper system in areas where the rail is hogging. These problems may be addressed by future work to develop an improved bending model, which can supply revised input to the crack growth model. Using the new crack growth model runs were carried out at 1500MPa contact pressure for water lubricated conditions with a semi-circular crack inclined at 30 degrees below the rail surface. Results showed that for semi-circular cracks of less than 35-40mm internal length (i.e. approximately 18-20mm depth) the bending stress element of the stress intensity factor cycle seen by a crack was of much lower magnitude than the contact stress component. Minor changes in stress intensity factor range were produced through changes in crack closure and locking, but for cracks of these lengths it was predicted that the stress intensity factor range, and hence crack growth rate, is not greatly influenced by rail bending. At crack lengths over 40mm bending stresses were predicted to become increasingly important, as would be expected from previous modelling work. It was found that bending stresses may subject a crack to multiple stress cycles per wheel pass, giving accelerated growth of cracks through both high stress intensity factors and three or fourfold increases in the number of stress cycles per wheel pass. Further investigation is required to understand how this multiple stress cycling affects cracks, and to check whether it is specific to the particular rail bending model (including two wheels on a short length of track) used in this work. This report contains revised information on the residual stress input data, and supersedes earlier versions of the report.
Publication type: Report
Source: NewRail, report WR061106-5
Publication year: 2006
Keyword(s): Contact stress; Crack growth; Hatfield; Railway rail; Residual stress; Rolling contact fatigue
Publisher: NewRail, Newcastle University
Publisher URL: http://www.ncl.ac.uk/newrail/
Peer reviewed