CURVE SQUEAL OF TRAIN WHEELS, PART 2: WHICH WHEEL MODES ARE PRONE TO SQUEAL?

This paper presents a frequency-domain analysis of a friction-driven wheel that is responsible for wheel squeal. A linear friction characteristic is assumed. The wheel motion is written as a superposition of bending modes. The modal properties (damping, frequency, impulse response amplitude of each mode) of the free wheel are known; the equivalent properties of the friction-driven wheel are calculated from complicated sets of linear and non-linear equations derived from the governing equation, which is an integrodifferential equation for the wheel displacement. An approximate analytical criterion is obtained, which allows one to predict easily whether a mode with given free-wheel properties is prone to squeal. The influence of features of the friction characteristic is also revealed. Precise numerical simulations give the growth rates, frequencies and complex amplitudes of the friction-driven wheel. These properties can be combined to give the time history of the wheel velocity. Time histories obtained in this way are compared with those obtained from direct evaluation of the governing equation in the time domain. Such comparison provides a reliable test of the time- and frequency-domain analysis.