| ||Format||Pages||Price|| |
|PDF (892K)||30||$25||  ADD TO CART|
|Complete Source PDF (5.7M)||224||$69||  ADD TO CART|
Detail fractures have been observed in railroad rails for many years and some serious railroad accidents have been attributed to these insidious rail defects . In a study completed in the early 1980s for the Department of Transportation , it was found that nearly 10% of over 10 000 1.6-km segments of revenue-service railroad rail contained one or more detail fracture defects. Although in the aggregate, detail fractures are relatively uncommon. (They comprised only about 3½% of the 30 000 defects observed in the study cited in Ref 2.) These defects are of great concern in terms of rail reliability and safety since detail fractures typically initiate and grow within the head of the rail, and they may go unidentified until the strength of the rail is so deteriorated that a sudden failure occurs, which can lead to a train derailment.
Over the past decade, Battelle has worked closely with the Volpe National Transportation Systems Center (VNTSC) and the Federal Railroad Administration (FRA) on the problem of shell and detail fracture formation in railroad rails [3–7]. This problem remains a significant one for the rail transportation and freight industry, in spite of the fact that a considerable body of knowledge now exists regarding the cause of these defects.
This paper was prepared in the form of a case study for fatigue education to give students interested in the discipline an opportunity to test their growing expertise on this real-world, present-day engineering issue.
This paper is presented in three parts. The first part of the paper is informational. It provides a brief description of shell and detail fractures in railroad rails, and offers a variety of examples of both types of defects. Other potentially important information for the case study is also provided, including: (1) typical three-dimensional residual stress data on used rails, (2) wheel/rail loading spectra, (3) thermal stresses in rail, (4) approximate “live” stresses induced in rails by passage of railroad wheels, and (5) crack initiation and fatigue crack growth properties of rail steel.
The second part of the paper reviews some of the fundamental questions that the railroad community has faced regarding shell and detail fractures in rails. The student is asked to take the role of an independent researcher, perhaps working for the railroad community. The task is to assess the available information and provide informed responses to each of these questions (and perhaps others that arise in class discussions).
The third part of the paper provides a discussion on each of the questions posed in Part 2. An overall interpretation of shell and detail fracture formation processes is also offered, along with some comments on steps taken by the railroad industry to minimize their occurrence and reduce the risk that those that do occur will lead to rail failures.
For use as a case study for fatigue education, it is recommended that the three parts of this paper be given to students sequentially over a period of time sufficient to allow an independent evaluation of related literature. In this way each response in Part 3 can be used more as an example of one plausible solution to the problem, rather than the only solution.
railroad rails, fatigue analysis, shelling, detail fractures, transverse defects, residual stresses, case study, failure analysis
Manager, Batelle, Structural Integrity Projects Office, Columbus, OH