Railway Track & Structures 12/07

speed, a stiff commuter suspension (bending stiffness = 1.2e9inch-pounds/rad, Kshear=70000 pounds/inch) with an 8.5-foot wheelbase, a 33-inch-diameter wheel and a 53.25inch wheel back-back. A lightly worn wheel profile with a 76-degree maximum flange angle is run against three different outside rails to provide conformal and non-conformal oneand two-point contacts. The three friction conditions used are tabulated at the top of this page. Note that none of these cases are particularly extreme, since dry rail friction coefficients upwards of 0.7 have been measured, while welllubricated rail could have a friction coefficient as low as 0.05. A quasi-static curving model was then applied to examine the effect of wheel/rail contact geometry, friction conditions and suspension type on wheel climb. Under the conditions examined, the following general conclusions can be made: Lubrication: Gauge-face lubrication increases lateral forces (Figure 4A), but, because it simultaneously increases the threshold wheel-climb limit, the net result is a reduction of the wheel-climb index (Figure 4B), i.e., wheel climb is less likely to occur. The safest case, where the wheel-climb index is minimized, occurs when the wheel/rail interface is friction managed, a process that includes lubrication of the gauge face and friction control of the top-of-rail to a value of about 0.35. Wheel/rail profiles: (Figure 4) A two-point contact develops lower longitudinal forces since the two contact points are “fighting each other” in the longitudinal direction. As a result of the lower steering moments, it generates higher angles of attack and can develop stronger lateral forces and hence higher L/V ratios. Suspension: (Figure 5) Stiff commuter trucks with a long wheelbase exhibited significantly higher wheel-climb indices than the shorter and more flexible freight bogie, at least for the few cases run in this exercise. Note that curving conditions probably exist where unfavorable steering moments with hollow wheels, for example, could cause the flexible freight suspension to develop greater yaw angles and higher lateral forces than the commuter cars. Flange Angle: (Figure 6) Lower flange angle wheels exhibit a significantly higher wheel-climb index than the higherflange-angle wheels. In some cases, the index almost doubles as the flange angle changes from 78 degrees to 68 degrees. This High Rail Lubrication condition Both dry Gauge-face lubricated Friction controlled TOR GF Low Rail TOR GF 0.45 0.45 0.45 0.2 0.35 0.2 0.45 0.45 0.35 0.45 0.2 0.2 factor far outweighs other aspects of the contact conditions such as whether the wheel and rail are matched with one or two points of contact, or are conformal or non-conformal. A second stage of wheel-climb studies is being undertaken at the National Resarch Council Canada, Centre for Surface Transportation Technology with support from the FRA Office of Research and Development. The goal of the upcoming work is to confirm the validity of the Nadal and Weinstock indices under dynamic situations using multi-body dynamics software. The authors would like to express their appreciation to the Federal Railroad Administration, and, in particular, Ali Tajaddini and Magdy El-Sibaie, for their support of this and other studies aimed at improving understanding of wheel/rail interaction problems in railroad systems and disseminating the information to interested parties. References 1. Railway Age, October 2007 2. A. O. Gilchrist and B.V. Brickle, “A re-examination of the proneness to derailment of a railway wheelset,” Journal of Mechanical Engineering Science, vol. 18, no.3, pp 134-141, 1976. 3. Kalker, J. J., “Survey of wheel-rail rolling contact theory,” Vehicle Systems Dynamics, Vol. 5, 1979. 4. H. Weinstock, “Wheel-climb derailment criteria for evaluation of rail vehicle safety,” Paper no. 84-WA/RT-1, Winter Annual Meeting of the American Society of Mechanical Engineers, Nov. 1984. 5. One milliradian (mrad) is approximately 1/60th of a degree. 6. F. B. Blader, “A Review of literature and methodologies in the study of derailment caused by excessive forces at the wheel/rail interface,” AAR Report No. R-717, 1990. www.rtands.com Railway Track & Structures December 2007 41 http://www.rtands.com

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Railway Track & Structures - December 2007 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Hand-Held Tools Provide the Power to Get Big Jobs Done AREMA C&S Update Striving to Solve the Riddle of Wheel Climb RTA Stages Warm Gathering in Sunny Florida in October Products and Literature People Calendar Website Directory Advertisers Index Sales Representatives Professional Directory Classified Advertising Chicago Perspective

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