TTCI R&D
THE NEXT GENERATION: AAR-2A A new standard wheel profile is providing multiple benefits.
T
he AAR-2A, a new standard wheel profile recently implemented for use in North American freight railway operations, is expected to provide improved service performance for wheelsets. This assessment is based on the analysis, simulation and testing conducted by Transportation Technology Center, Inc. (TTCI). The new AAR-2A wheel profile was designed to produce a nearly conformal contact condition with a typical rail on the high side of a curve to provide benefits such as improved steering and minimized rolling resistance, wear, fuel consumption and surface damage. Compared to the older AAR-1B profile, the AAR-2A produces a more-even distribution of wear across the wheel flange and tread such that 30 Railway Age // June 2020
the profile shape does not change substantially during the service life of the wheel. Analytical evaluation, computer simulation and service testing were used over the course of multiple years to ensure that the design goals of the AAR-2A profile were met. Each method of evaluation showed improved curve performance of the AAR-2A profile compared to the AAR-1B profile. Starting with turned wheels, implementation of the AAR-2A profile has been under way since 2016, and it became the primary standard profile in North American freight operations in January 2020. Although service-worn freight car wheel and rail profiles show a wide distribution in gross shapes, they generally wear to similar shapes in the wheel flange root and high rail gage corner. The annual replacement rates of wheels and rails strongly
imply that the majority of wheels and rails in service at any time will exhibit worn profiles that can potentially diverge substantially from their as-manufactured shapes. Rail grinding is used to control rail profile shapes, but grinding templates are not designed to restore the rail to the as-manufactured shape. Development of the AAR-2A wheel profile started with the collection of measured service-worn wheel and rail profiles to aid in the investigation of the distributions and patterns of worn wheel and rail profile shapes. Curves were fit to match the most commonly worn shapes of the high rail gage corners and wheel flange roots. In comparison to the AAR-1B profile, the AAR-2A profile contains more material in the flange fillet to reduce and/ or eliminate the strong two-point contact that occurs when the wheel makes flange contact railwayage.com
William C. Vantuono
BY SCOTT CUMMINGS, SCIENTIST, TRANSPORTATION TECHNOLOGY CENTER, INC.
