Nonlinear vibration signatures for localized fault of rolling element bearing in rotor-bearing-casing system

Fault signatures in the vibration signal are an important basis for diagnosis of localized defects in a rolling element bearing. Normally the defect-induced impulses will result in harmonics of the fault characteristic frequency and sidebands in the demodulated spectrum. But there will be obvious difference for fault signatures of different bearings with different surroundings, especially the shape of the modulation sidebands. This paper gives an explanation on the causes and influencing factors of bearing fault signatures using an impulse sequence model and a nonlinear multi-body dynamic bearing model in the rotor-bearing-casing system. The frequency components of the load force function on the defect will affect the amplitude of the impulses due to contact loss, becoming the modulation sidebands of the fault characteristic frequency. The extend of the load distribution on rolling elements are controlled by the initial bearing clearance, while the load force function on the defect is given by substituting the estimation of the load force on the bearing and the motion of the defect into the load distribution function. The influence of the defect position and random fluctuations are also analyzed in the simulation, as well as multiple localized defects of the same or different types. The numerical and experimental results show that this modeling and analysis method could be applied to explain and estimate fault signatures of localized bearing faults in a typical rotor-bearing-casing system.