Impact Response Characterization as basis for Bearing Diagnostics and Prognostics

Impact response due to sudden changes on the contact forces is an intrinsic phenomenon at all stages of the bearing life. Even prior to the actual occurrence of surface damage, short duration impacts occur in the case of insufficient lubrication where asperities or particles interact with the surface of its mating element. As the surface condition deteriorates, the energy released by the impacts increases affecting structural modes. As soon as the system condition worsens, lower frequencies are excited and consequently increased vibration levels are displayed. The impulse response function reflects the modulation phenomena between contact forces, structural resonances and driving forces taking place in the bearing and the mechanical system that contains it. The characterization of the components of the impulse response becomes then a valuable tool for vibration monitoring. This article is framed within the research on development of advanced vibration monitoring systems, for which the authors follow a systemic approach in the definition of the monitoring requirements based on the function-failure analysis of the monitored object. The discussion focuses on the correspondence between the monitoring and monitored systems, by analyzing the impulse behavior as illustrated by the train bearings. The comparative analysis between environment and damage induced impacts highlights the different stages in bearing damage.