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Keywords: head-hardened steel, rolling contact, fatigue, fracture mechanics, R-value, lifetime.

Summary

Head hardened steel rails are continuously replacing conventional steel rails because they exhibit a much lower wear rate in rolling contact fatigue. However, with decreasing wear rate, the fracture toughness of the rail steel also decreases and the hardened rail heads become very susceptible to surface cracking. The combined action of the various stresses due to rolling contact, mechanical bending, residual, and thermal loadings on the rail has a tremendous effect on the lifetime of the rail.

When a typical surface-breaking fatigue crack develops in a head-hardened steel rail it is subjected to these four types of loading. The passage of a train causes a sequence of compressive and tensile stress peaks in the rail head. Superposition of the four stresses leads to a shift of the mean stress into the tensile or compressive regime depending on the seasons, winter or summer. One important feature is a change of the number of cycles with the elevation of the tensile stresses.

The lack of residual stresses and mechanial bending stresses in certain sections of the Vienna subway explains the fact that the original rails are still in service, for more than thirty years. And it also explains why, in a few sections, rails had to be changed after the relatively short service period of two years.

This paper addresses the lifetime of head-hardened steel rails used in the Vienna metro system. Metro steel rails are subjected to a variety of stresses such as stresses due to rolling contact, thermal stresses due to changing climatic seasonal conditions, residual stresses due to rail manufacturing and straightening and occasionally bending stresses due to improper bedding of the rails. These stresses are responsible for the magnitude of the fracture mechanics related R-value. It will be shown that residual stresses and bending stresses can be made responsible for a dramatic increase of the stress variation and the number of cycles. Examples from the Vienna subway lines, Wiener Linien, are presented in the paper.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 98 PROCEEDINGS OF THE FIRST INTERNATIONAL CONFERENCE ON RAILWAY TECHNOLOGY: RESEARCH, DEVELOPMENT AND MAINTENANCE Edited by: J. Pombo Paper 102 The Effect of the R-Value on the Lifetime of Cracked Head-Hardened Steel Rails for Subways H.P. Rossmanith and J. Broger Institute of Mechanics and Mechatronics, Vienna University of Technology, Austria doi:10.4203/ccp.98.102 purchase the full-text of this paper Full Bibliographic Reference for this paper H.P. Rossmanith, J. Broger, "The Effect of the R-Value on the Lifetime of Cracked Head-Hardened Steel Rails for Subways", in J. Pombo, (Editor), "Proceedings of the First International Conference on Railway Technology: Research, Development and Maintenance", Civil-Comp Press, Stirlingshire, UK, Paper 102, 2012. doi:10.4203/ccp.98.102 Keywords: head-hardened steel, rolling contact, fatigue, fracture mechanics, R-value, lifetime. Summary Head hardened steel rails are continuously replacing conventional steel rails because they exhibit a much lower wear rate in rolling contact fatigue. However, with decreasing wear rate, the fracture toughness of the rail steel also decreases and the hardened rail heads become very susceptible to surface cracking. The combined action of the various stresses due to rolling contact, mechanical bending, residual, and thermal loadings on the rail has a tremendous effect on the lifetime of the rail. When a typical surface-breaking fatigue crack develops in a head-hardened steel rail it is subjected to these four types of loading. The passage of a train causes a sequence of compressive and tensile stress peaks in the rail head. Superposition of the four stresses leads to a shift of the mean stress into the tensile or compressive regime depending on the seasons, winter or summer. One important feature is a change of the number of cycles with the elevation of the tensile stresses. The lack of residual stresses and mechanial bending stresses in certain sections of the Vienna subway explains the fact that the original rails are still in service, for more than thirty years. And it also explains why, in a few sections, rails had to be changed after the relatively short service period of two years. This paper addresses the lifetime of head-hardened steel rails used in the Vienna metro system. Metro steel rails are subjected to a variety of stresses such as stresses due to rolling contact, thermal stresses due to changing climatic seasonal conditions, residual stresses due to rail manufacturing and straightening and occasionally bending stresses due to improper bedding of the rails. These stresses are responsible for the magnitude of the fracture mechanics related R-value. It will be shown that residual stresses and bending stresses can be made responsible for a dramatic increase of the stress variation and the number of cycles. Examples from the Vienna subway lines, Wiener Linien, are presented in the paper. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £110 +P&P)
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