STP644

    Fatigue and Fracture Behavior of Carbon-Steel Rails

    Published: Jan 1978


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    Abstract

    The Ad Hoc Committee on Rail Research, which is composed of representatives from the American Railway Engineering Association (AREA), the Association of American Railroads (AAR), and the American Iron and Steel Institute (AISI) Committee on Railroad Materials, formulated a program to investigate the effects of metallurgical properties, mechanical properties, and applied stress conditions on the service fracture behavior of carbon-steel rails. This paper presents the fatigue and fracture behavior of five rails having extremes in room-temperature tensile properties and Charpy V-notch toughness, and an analysis of the effect of this behavior on the in-service useful life of carbon-steel rails. These five rails were removed from service after 15 to 18 years of operation and were selected from a population of about 90 rails that were removed from service because they contained service-developed defects. A companion paper in this symposium describes the results of chemical analysis, hardness and tension tests, and the results of wear, deformation, metallographic, and fractographic analysis.

    The results of the fractographic investigation conducted under AAR-AISI contract that are presented in part in the companion paper showed that in-service fatigue cracks initiated from inclusions having a width of about 0.03 mm (1.25 mils). The results of the present investigation showed that fatigue crack initiation from such small discontinuities occurs when the magnitude of the stress fluctuations applied to the railhead with the passage of each wheel are equal to about the tensile strength of the steel. The cost of the steelmaking practices required to eliminate such small discontinuities is believed to be economically prohibitive. Moreover, the detection of such discontinuities is beyond the capabilities of presently available nondestructive inspection procedures. The results also showed that the fatigue crack propagation behavior of various carbon-steel rails is essentially identical and is independent of chemical composition or mechanical properties. Moreover, the dynamic fracture toughness of these rails at the minimum operating temperature of about -351°C (-30°F) was about 27.5 MPa m (25 ksi in.), and a significant increase in the fracture toughness of the rail would result in a negligible increase in the useful fatigue life of the rail. Significant increase in the fatigue life of rails can be achieved by decreasing the wheel load, by maintaining the roadbed, by changes in the design of rails, and by establishing a residual compressive stress field in the upper portion of the railhead which can be accomplished, for example, by induction hardening. Consequently, it is suggested that the safety and reliability of rails can be ensured best by decreasing the magnitude and fluctuation of the stresses in the rail and by periodic nondestructive inspection of rails.

    Keywords:

    steels, railroad tracks, metallurgy, mechanical properties, stresses, fracture, fatigue


    Author Information:

    Barsom, JM
    Section supervisor and senior research technician, United States Steel Corporation, Research Laboratory, Monroeville, Pa

    Imhof, EJ
    Section supervisor and senior research technician, United States Steel Corporation, Research Laboratory, Monroeville, Pa


    Paper ID: STP27118S

    Committee/Subcommittee: A01.01

    DOI: 10.1520/STP27118S


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