Interface - The Journal of Wheel/Rail Interaction

WHEEL RAIL INTERACTION

Tuning in to the Systems Approach
By Bob Tuzik • July, 2007

You’ve heard it before, you’ll hear it again. Delegates to the 13th Annual Wheel/Rail Interaction Seminar presented by Interface Journal and Advanced Rail Management heard it time and again over the course of the seminar: The wheel/rail interface is a system. And when there are problems, as there often are, it takes a systems approach to solve them.

Sometimes the problems are related to performance and wear, and the costs associated with them. Sometimes they’re related to component failures that sometimes lead to derailments.

The Hatfield derailment in late 2000 caused a severe disruption and loss of passenger confidence in the UK. With the bad, however, came some good: “The derailment stimulated investigation into and understanding of some of the root causes of poor rail/track conditions, such as cracks in the rail and rolling contact fatigue, in particular,” said Kevin J Sawley, Principal Consultant, Interfleet Technology Ltd.

Field investigation and analysis indicated that there were three primary modes of crack initiation:

— Steady state curving, which is caused by high steering forces and occurs in curves of less than 2 degrees.

— Bi-stable contact, which occurs when small wheelset lateral shifts cause a sudden large change in rolling radius and, thereby, generate a longitudinal force. Bi-stable contact is symptomatic of conformal wheel/rail profiles, and occurs in curves of 1 - 2 degrees.

— Convergent motion, which is caused by short-wavelength lateral rail misalignment that the wheelset cannot follow. Convergent motion causes a sudden large change in rolling radius, along with the associated longitudinal force, and occurs in very shallow curves and nominally tangent track.

Remediation methods for the crack-initiation modes include rail grinding (primary) and lubrication (secondary) for steady state curving; grinding (primary) and track alignment (secondary) for bi-stable contact; and track alignment (primary) and rail grinding (secondary) for convergent motion.

“Grinding and friction modification are essential, but they are band aids,” Sawley said. “We need to find ways to reduce the amount of energy spent and wear.”

Through extensive research into wheel/rail interaction, methods have been found to predict wear and RCF. Software programs such as NUCARS® and VAMPIRE® can now apply “what if” queries that can be used to guide vehicle and track design and maintenance, and the business decisions associated with them.

Dark Territory
Norman E. Hooper, Project Engineer, Hatch Mott MacDonald reported on measures that can be taken to reduce broken rail derailments in dark territory. During a three-year period ending in September 2006, broken rails accounted for 40% of all FRA-reported, track-related derailments on main track. Temperature differentials, residual stress, axle loading, accumulated tonnage, wear, track modulus, wheel impacts and other factors can contribute to the frequency of broken rails. While these factors affect all railways, they are particularly problematic in “dark territory” where the absence of a signal system that can alert a railway to a broken rail can go undetected until “found” by a train — a circumstance that often ends in derailment, Hooper said.

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