Steps toward prognostics of faults in bearings

Assessment of the remaining useful life of a rolling-element bearing is a key element in rotating machines prognostics. Evaluation of the bearing remaining useful life (RUL) requires diagnosis of the fault existence, estimation of its size and estimation of the time interval until it reaches a critical size. A concept for bearing RUL estimation is proposed. The main insights which led to the concept development are reviewed. The study focuses on estimation of spall size located in one of the bearing races. A new approach for estimation of spall size in bearing races is developed based on physical insights obtained from results of a general bearing dynamic model. Analytical modeling of the interaction between the spall and the rolling element enables the development of an autonomous generic method for spall size estimation. In this paper, the principles for spall size estimation are described. The new method was applied to experimental data including different spall sizes on inner and outer races. The estimation shows satisfactory results with errors up to 20%.