Damage identification at rolling contact bearings

White Etching Cracks (WECs) and White Etching Areas (WEAs) are failure modes, which appear prevalently in rolling contact bearings. There is still a lack of methods to identify such failure modes before the visible crack appears on the bearing surface as early as possible. In this article the measured operational deflection shapes (ODS) from a rolling contact bearing with and without WECs and WEAs are compared. The measurement was obtained by using our vibrometer system, which is mounted on a robot. The measured ODS's are compared by using the ordinary coherence, Frequency Response Assurance Criterion (FRAC) and Cross Signature Assurance Criterion (CSAC) for checking their correlation. The results show that the ODS's from the bearing with and without WECs and WEAs are not correlated in the hole frequency spectrum. Therefore monitoring the ODS's of the bearing by using the three comparing criterions seems to be feasible to detect the existence of WECs or WEAs in bearings. Online measuring ODS's require surface vibration measurements which should be realized by simultaneous measurement techniques with multiple channels.