Proposed alternative test procedure for AAR specification M-965-91 with the vibration test unit

An investigation into a possible alternative test procedure for the Association of American Railroads´ (AAR) Specification M-965-91, sponsored by the Standard Car Truck Company, was performed on the Vibration Test Unit (VTU) in the Rail Dynamics Laboratory at the Transportation Test Center (TTC), Pueblo, Colorado. The results show that the VTU was able to excite responses of the test car which, when compared to on-track test data, showed similarities in characteristics (i.e. critical speed was clearly evident in both cases) but not in regards to absolute values of response amplitudes and critical speeds. The referenced specification, “Special Devices to Control Stability of Freight Cars,” originally involved the testing of trucks for roll stability on a car rocker located at Norfolk Southern´s research and test facility in Alexandria, Virginia. When that rocker was no longer available, the specification was amended to allow certification to be achieved through tests over a track which contains 0.75-inch cross level variations designed to determine roll behavior. The modified certification procedure required the test car to traverse the twist-and-roll track section at constant speed, increasing in 1 mph increments from 12 mph to 25 mph. Criteria for the revised certification procedure required lateral to vertical wheel force ratios (L/V) to be less than 1.4, roll angles to be less than 6 degrees peak-to-peak, and minimum vertical wheel loads not to be less than 25 percent of static value through the wheels and axles