TIMEOUT FOR TECH
Figure 1. Transverse fatigue crack in a broken railroad rail. (Courtesy of Gary T. Fry.)
METAL FATIGUE How dangerous fatigue cracks develop in sound steel.
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elcome to “Timeout for Tech with Gary T. Fry, Ph.D., P.E.” Each month, we examine a technology topic that professionals in the railway industry have asked to learn more about. This month, our topic is fatigue cracks in steel. Figure 1 (above) is a photograph of the head of a broken railroad rail. The fracture of this rail originated from internal transverse fatigue cracks. Fortunately, before a
36 Railway Age // January 2022
train found these defects, the Class I railroad’s inspectors found them using technology that can scan inside the solid steel. The defective portion of rail was removed, and sometime later the rail owner used a loading frame to break the rail open and expose the defects. That’s the type of successful scenario we like to hear about. The fitness for service assessment program worked exactly as it should. But isn’t it somewhat frustrating, disconcerting even, that we must remain on guard against fatigue failures in steel?
Can’t we invent a “fatigue-proof ” steel? It sounds like a great idea to me, but I’m afraid I have disappointing news on that front. We rely upon certain forms of imperfections in the atomic lattice of iron to provide essential structural properties of steel, such as strength, ductility and fracture toughness. It is these same atomic-scale imperfections that cause fatigue cracks to form. Let’s have a look at the details. The steel used to manufacture today’s railroad rail is a carbon steel railwayage.com
Gary T. Fry
BY GARY T. FRY, PH.D., P.E., VICE PRESIDENT, FRY TECHNICAL SERVICES, INC.