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Keywords: RCF, influence of third body materials, pre-existing cracks.

Summary

Control of rolling contact fatigue (RCF) is a critical maintenance activity. Practical means of mitigating RCF involve, 1) preventative grinding to remove RCF cracks at an early stage, 2) management of wheel / rail profiles to minimize peak contact pressures, and 3) Selection of appropriate rail metallurgy. In addition, reduction of traction forces by application of Top of Rail friction modifier has recently been shown to reduce crack growth and extend grinding intervals. Hydro-pressurization and crack face lubrication are processes by which liquid materials (e.g. water) enter pre-existing RCF cracks and under wheel / rail pressure causes accelerated crack growth, leading to spalling and shelling on rail and wheels. Thus any liquid material added deliberately to the wheel/rail interface should be considered carefully in terms of the potential for aggravated RCF damage. In this study the impact on hydro-pressurization and crack face lubrication of different types of materials designed for application to the Top of Rail were compared. One type of material is water based and dries to a thin dry film, two other types are oil based that do not dry, and have been introduced more recently to the market. In addition a commonly used gauge face lubricant (grease) was evaluated. Twin disc testing used R8T wheel material and 260 grade rail. RCF cracks were first generated under dry conditions, then friction control materials were applied. The test continued for a fixed number of cycles, and samples were evaluated at the end. Results show that all the non-drying oil based materials caused significant rail damage (spalling) consistent with a hydro-pressurization and crack face lubrication mechanisms. By contrast the dry film material showed no such damage, and prevented further growth of the RCF cracks. These results suggest considerable care should be employed in deploying nondrying oil based materials where pre-existing RCF cracks can occur, e.g. in curves. Careful field testing is recommended to further evaluate this issue clearly seen under laboratory conditions.

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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: 104 PROCEEDINGS OF THE SECOND INTERNATIONAL CONFERENCE ON RAILWAY TECHNOLOGY: RESEARCH, DEVELOPMENT AND MAINTENANCE Edited by: J. Pombo Paper 181 The Effects of Alternative Top of Rail Friction Materials on Pre-Existing Rolling Contact Fatigue Cracks C. Hardwick and R. Lewis Department of Mechanical Engineering, The University of Sheffield, United Kingdom doi:10.4203/ccp.104.181 purchase the full-text of this paper Full Bibliographic Reference for this paper C. Hardwick, R. Lewis, "The Effects of Alternative Top of Rail Friction Materials on Pre-Existing Rolling Contact Fatigue Cracks", in J. Pombo, (Editor), "Proceedings of the Second International Conference on Railway Technology: Research, Development and Maintenance", Civil-Comp Press, Stirlingshire, UK, Paper 181, 2014. doi:10.4203/ccp.104.181 Keywords: RCF, influence of third body materials, pre-existing cracks. Summary Control of rolling contact fatigue (RCF) is a critical maintenance activity. Practical means of mitigating RCF involve, 1) preventative grinding to remove RCF cracks at an early stage, 2) management of wheel / rail profiles to minimize peak contact pressures, and 3) Selection of appropriate rail metallurgy. In addition, reduction of traction forces by application of Top of Rail friction modifier has recently been shown to reduce crack growth and extend grinding intervals. Hydro-pressurization and crack face lubrication are processes by which liquid materials (e.g. water) enter pre-existing RCF cracks and under wheel / rail pressure causes accelerated crack growth, leading to spalling and shelling on rail and wheels. Thus any liquid material added deliberately to the wheel/rail interface should be considered carefully in terms of the potential for aggravated RCF damage. In this study the impact on hydro-pressurization and crack face lubrication of different types of materials designed for application to the Top of Rail were compared. One type of material is water based and dries to a thin dry film, two other types are oil based that do not dry, and have been introduced more recently to the market. In addition a commonly used gauge face lubricant (grease) was evaluated. Twin disc testing used R8T wheel material and 260 grade rail. RCF cracks were first generated under dry conditions, then friction control materials were applied. The test continued for a fixed number of cycles, and samples were evaluated at the end. Results show that all the non-drying oil based materials caused significant rail damage (spalling) consistent with a hydro-pressurization and crack face lubrication mechanisms. By contrast the dry film material showed no such damage, and prevented further growth of the RCF cracks. These results suggest considerable care should be employed in deploying nondrying oil based materials where pre-existing RCF cracks can occur, e.g. in curves. Careful field testing is recommended to further evaluate this issue clearly seen under laboratory conditions. 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 £65 +P&P)
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