Verification Testing of the Bearings Used in the Electrohydraulic Total Artificial Heart

Abstract

This article reports the verification testing performed on the ball bearings used in the electrohydraulic total artificial heart (EHTAH) device. The bearings were tested for 70 days under conditions intended to simulate those actually experienced by the bearings in the EHTAH device. Vibration analysis to predict the condition of the bearings, as well as diagnosis of the wear experienced by the bearings, was included in this study. Examination of the bearings using light microscopy indicated the presence of wear, and in some instances the contact surfaces had undergone temper coloring, a warning sign that hardness of the bearing may have been impaired, and that the bearing has experienced a temperature excursion. Temper coloring can be caused by too thick a coating of grease or by insufficient hydrodynamic film thickness. In this investigation, the vibration amplitudes at specific frequencies that correlated with the bearing components were monitored for change. From analysis of the vibration spectra, it was found that the change in amplitude did not predict the damage incurred by the bearings. The type of damage experienced by the bearings is difficult to predict using spectral analysis.