United States Department of Transportation
i
Sleeve Expansion of Bolt Holes in Railroad Rail : Volume I, Description and Planning
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1980-02-01
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[PDF-3.66 MB]
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Abstract:The most predominant failure mode of rails with bolt joints is a web crack initiating at the rail bolt hole. This failure mode is of a classical fatigue nature induced by web stress concentration around the bolt hole. This program was conducted to apply a metal-working process to the rail bolt hole to reduce the effect of such stress concentration and to demonstrate the effectiveness of the technique. Using a process known as cold hole expansion, common to the aircraft industry, where the bolt hole is expanded to the point of plastic deformation, a residual compressive stress of both radial and tangential components is formed around the bolt hole. The compressive stress developed effectively reduces the failure-initiating stress concentration at the bolt hole. The effectiveness of the cold-expansion process as applied to rail was demonstrated by comparison fatigue testing of both cold-expanded (CE) and non-cold-expanded (NCE) specimens. Laboratory tests indicated that life improvement for CE specimens was such that web or head failures would be the predominant failure mode, rather than CE bolt holes. The test results were statistically analyzed, indicating a factor of 10 or greater improvement in rail life due to reduction in bolt-hole failure could be anticipated. Experimental equipment was adapted to apply cold hole expansion to an 8.5 mile test section of track in commercial service. Evaluation of this field test is continuing.
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