Experimental quantification of dynamic forces and shaft motion in two different types of backup bearings under several contact conditions

• Experimental quantification of contact forces in two different types of backup bearings.
• Experimental quantification of contact forces during rotor–stator impacts and full annular whirl motions.
• Analysis of contact force hysteresis.
• Elimination of full annular whirl and whip motions using unconventional pinned backup bearing.

This paper treats the experimental study on a shaft impacting its stator for different cases. The paper focuses mainly on the measured contact forces and the shaft motion in two different types of backup bearings. As such, the measured contact forces are thoroughly studied. These measured contact forces enable the hysteresis loops to be computed and analyzed. Consequently, the contact forces are plotted against the local deformation in order to assess the contact force loss during the impacts. The shaft motion during contact with the backup bearing is verified with a two-sided spectrum analyses. The analyses show that by use of a conventional annular guide, the shaft undergoes a direct transition from normal operation to a full annular backward whirling state for the case of external excitation. However, in a self-excited vibration case, where the speed is gradually increased and decreased through the first critical speed, the investigation revealed that different paths initiated the onset of backward whip and whirling motion. In order to improve the whirling and the full annular contact behavior, an unconventional pinned backup bearing is realized. The idea is to utilize pin connections that center the rotor during impacts and prevent the shaft from entering a full annular contact state. The experimental results show that the shaft escapes the pins and returns to a normal operational condition during an impact event.