Abstract
The study provides an accurate measurement of the longitudinal and lateral traction under precisely controlled angles of attack conditions, using the Virginia Tech-Federal Railroad Administration roller rig (“VT-FRA roller rig”). The tests are performed under field-simulated conditions that allow wheel wear and accumulation of worn material at the running surfaces, with angles of attack (AOA) that represent both left- and right-hand curves. Because the roller rig allows testing under extreme conditions, AOAs as large as two degrees (0.035 radian) are evaluated for a scaled wheel with a nominal AAR-1B profile. It is observed that the longitudinal and lateral traction coefficients increase with increasing time, for all AOAs, but far more significantly for large AOA. The effect is nonlinear, meaning that for shallower (lower-degree) curves the friction effect is far less than for steeper (higher-degree) curves. It is further observed that the influence is asymmetric for right- and left-hand curves. The wheel taper introduces a lateral force that adds or subtracts (depending on the orientation of the curve) from lateral curving forces. The curving forces resulting from a positive AOA (corresponding to a left-hand curve) are less than those for negative AOAs, mainly due to the force offset due to the wheel taper.
