Stiffness and Friction Force Measurements on a Freight Car Truck from Quasi-Static Tests

A conventional three-piece truck with load sensitive friction snubbing was tested as a complete assembly with its wheels resting on a fixed section of rail and with loads applied through a fixture that duplicated the body bolster at the truck bolster interface. The purpose of the testing was to determine the stiffness and friction forces of the truck under vertical, lateral, and roll moment loading conditions. Loads were varied to cover a range of car gross weight conditions. The test was quasi-static in that load application was varied at sinusoidal rates of 0.1 or 0.2 Hertz to minimize errors in spring rate measurement caused by friction snubber forces. The desired stiffness and friction force data were obtained in terms of system rather than component properties and are consequently more directly usable in mathematical models. The roll test data were particularly useful because separate spring rates were obtained for the different conditions of center plate seated, center plate rocking, and side bearing contact. Because of the sinusoidal method of load application, it was possible to obtain system spring rates with the friction snubbers static and sliding.