The use of Acoustic Emission for bearing defect identification and estimation of defect size

Vibration monitoring of rolling element bearings is possibly the most established diagnostic technique for rotating machinery. The application of Acoustic Emission (AE) for bearing diagnosis is gaining ground as a complementary diagnostic tool; however, limitations in the successful application of the AE technique have been partly due to the difficulty in processing, interpreting and classifying the acquired data. Furthermore, the extent of bearing damage from the defect has eluded the AE diagnostician. The investigation reported in this paper was centered on the application of the Acoustic Emission technique for identifying the presence and size of a defect on a radially loaded bearing. An experimental test-rig was designed such that defects of varying sizes could be seeded onto the outer race of a test bearing. Comparisons between AE and vibration analysis, over a range of speed and load conditions, are presented. It is concluded that not only does AE offer earlier fault detection and identification capabilities than vibration analysis but can also provide an indication of the defect size, thus allowing the user to monitor the rate of degradation on the bearing.