With the continuous increase in the operating speed of high-speed trains, faults for rotor-bearing systems have become increasingly prominent, posing a serious threat to train's operation safety. Among the various faults of rotor-bearing systems, bearing spalling not only affects the normal operation of the bearing itself but also alters the dynamic characteristics of the rotor-bearing system, thereby inducing additional frequency components and super-harmonic resonances, which greatly increase the difficulty of fault identification in train rotor-bearing systems. This paper focuses on spalling in deep-groove ball bearings of traction-motor rotor-bearing systems. Based on an analysis of the coupling among multiple excitations, a dynamic model is developed that simultaneously accounts for rotor unbalanced magnetic pull, mechanical unbalance forces, rubbing forces, gravity, the nonlinear supporting forces of a cylindrical roller bearing and the nonlinear supporting forces of deep-groove ball bearing with spalling. The model is validated against test-rig experiments. Quantitative analysis in the speed range of 1 000-5 000 rpm shows that outer-race, inner-race and rolling-element spalling generate clearly distinguishable fault characteristic bands and modulation sidebands. When rolling elements pass over a local spall, the contact force exhibits instantaneous jumps and intermittent loss, so that the RMS value of the nonlinear supporting force becomes about 2.4-3.4 times that of the corresponding healthy bearing. As the spall width increases, the RMS acceleration and supporting force grow monotonically at all speeds, with the amplification especially pronounced at 5 000 rpm. These quantitative findings provide a modeling reference and theoretical basis for fault diagnosis of rotor-bearing systems in high-speed trains.

Rotor-bearing system; Combined excitations; Bearing spalling; Dynamic modeling; Dynamic characteristics