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Rough Grinding and Rolling Contact Fatigue (RCF)

Description:

Transit systems have relatively light axle loads, and the residual post grind roughness due to rail grinding therefore can take considerable time to diminish completely. This residual roughness can contribute to excessive vehicle noise and other potential issues.

Research is needed to understand if and at what level rough grinding can contribute to the development of excessive vehicle noise and near surface fatigue cracks. Secondly, research is needed to evaluate the tradeoffs between rougher or finer stones in terms of the conflicting demands between productivity and surface quality (including roughness, noise, vibration and potential RCF and corrugation development).

Objective:

To determine whether high productivity, coarse grinding stones and the resulting surface finish of the rail contribute to rolling contact fatigue in a rail transit environment. A secondary objective is to evaluate the productivity tradeoff between coarse high material removal grind stones and fine less material removal grind stones.

Benefits:

Passenger and transit systems throughout North America grind rail on a regular basis. While some focus on noise and rail corrugation, for others there are strong concerns about rolling contact fatigue. Most are interested in the most cost effective approach to alleviating those issues and are unsure what level of surface finish is worth pursuing at a higher maintenance cost.

Related Research:

Rail profile designs and rail grinding strategies that optimize the amount of metal removed to treat surface condition problems have seen much attention in the last two decades. More recently there has been exploration of the impact of rail grinding on noise and rail corrugation, though this is in its infancy. Those efforts now underway could also be leveraged to explore the concern about surface fatigue cracking. Major rail grinding programs are underway in cities such as New York, Toronto, San Francisco, Seattle and Vancouver that can be called upon to support this investigation.

Complementary work on rail grinding quality indices is being conducted in collaboration with the University of Manitoba and in economic evaluations through an International Collaborative Research Initiative on RCF and wear of rails and wheels. Metallurgical work is ongoing through an FRA sponsored project to “Qualify Rail Surface Damage” that involves the collection of dozens of rail samples from industry for sectioning to compare visible surface damage with internal damage. It would be relatively cost effective to add the required rail samples to the ongoing work stream.

Tasks:

A literature review of the problem should be undertaken, looking not only to experience in North America, Australia and Europe but also across other industries if appropriate. Review of academic and theoretical work in this field (e.g. modeling of plastic deformation, crack initiation and propagation) should be undertaken.

It is expected that both laboratory and field testing would follow. While disc on disc testing is possible, scaling effects are always problematic and probably insurmountable for this study. And while full scale testing is possible, it is both expensive and possibly inconclusive since a realistic loading environment (e.g., combination of powered and non-powered wheels) that reflects the true operating conditions is difficult to define and more difficult to replicate. Accordingly, the problem would best be understood through analysis of in-service rail samples.

One or more railroads willing to remove rail samples with a variety of rail surface finishes both immediately after grinding work and after some level of accumulated traffic would be required.

Cracks on any collected samples would be sized using eddy current measurement and then metallurgically sectioned to look for tearing and cracking in the grinding furrows and evidence of plastic flow over furrows.

Other field testing would include grinding and monitoring two curves of similar makeup – one with high material removal grinding and one with acoustic grinding. Monitoring would include visual inspection (enhanced with magnetic particle highlighting as required) and eddy current. A portable single probe system such as the Elotest can be used to size single cracks for the detailed analysis required.

Follow-on activity

If it is determined that rough grinding is indeed the contributor to rolling contact fatigue, then a cost-benefit analysis is needed. While rough grinding is more productive and less costly on a pass-mile basis, if it contributes to RCF formation then the initial savings might be offset by the more frequent and heavier grinding required to remove surface defects arising more rapidly. A potential hybrid approach using first coarse and then fine stones to grind rail could be explored.

Implementation:

The research is likely to become part of a widely used rail grinding guideline by transit agencies. As such it will impact all agencies but clearly those more invested in maximizing the effectiveness of their rail grinding programs will take stronger notice of its impact. Rail grinding companies and wheel-rail consultants will be active in assuring its application to transit properties.

Relevance:

Increasing focus on the contribution of rail grinding to the elimination of, and contribution to, noise and vibration have raised the profile of rail grinding and current practices are being questioned. The push to finer grit stones is tempting but the cost of doing so is not inconsiderable. Answering the question posed by this RSN will provided a needed input to resolving the issue.

Sponsoring Committee:AR050, Railroad Infrastructure Design and Maintenance
Research Period:12 - 24 months
Research Priority:Medium
RNS Developer:Eric E. Magel, Principal Engineer, Rolling Contact Fatigue, National Research Council, Canada, eric.magel@nrc-cnrc.gc.ca, +1 250 317 0205 Mark Reimer, Director of Projects, Advanced Rail Management Corporation, Indialantic, Florida, mreimer@arm-corp.com, +1 204 792 7555
Date Posted:01/08/2021
Date Modified:05/20/2021
Index Terms:Rail grinding, Rolling contact, Maintenance of way, Alternatives analysis,
Cosponsoring Committees: 
Subjects    
Public Transportation
Railroads
Maintenance and Preservation

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