Advancements in Monitoring of Tribological Stress in Bearings Using Thin-Film Strain Gauges

Abstract

The world's electrical energy demand is rising permanently and, at the same time, resources must be used economically and responsibly. An important part of the energy turnaround are wind mills, where conventional machine elements such as gears or rolling bearings find application. These parts have optimization potential in terms of service life and reliability. To advance this potential, sensor integration for intelligent system monitoring combined with a compact electronic solution has to be realized. In contrast to conventional condition monitoring systems (CMS), this article addresses thin-film sensors that will be applied inside the bearing system directly inside or close to the tribological contact enabling maximum information about the system's condition. For this purpose, thin-film strain gauges are directly deposited onto small steel bearing washers of a cylindrical roller thrust bearing system (CRTB) by photolithography and sputtering processes. The layer stack includes an aluminum oxide insulation layer, the sensor layer and an aluminum oxide wear protection coating. The sensor layer consists of an array of three differently aligned meander-shaped constantan strain gauges. Therefore, bearing washers with the sensors are tested on a pin-onplate tribometer under defined load conditions. The influence of normal force as well as velocity on the thin-film sensors could be detected in this study. During the tests, under Hertzian pressure up to 1 GPa and a constant sliding velocity of 8 mm/s, a maximum nominal resistance change ΔR/R 0 of up to -0.13 ‰ was measured. Changing the velocity from 1 mm/s to 8 mm/s resulted in maximum ΔR/R 0 values of -0.17 ‰. This enables the determination of the correlation between sensor signals and tribological stresses. Though Hertzian pressures of 950 MPa were applied, no sensor failure was observed during the experiments proving the functionality of the sensor layer system.

Behavior of Lubricated Bearings in Electric Circuits

“…Another possibility is offered by printed sensors, such as those used by [32][33][34][35], but these are not yet for widespread use in bearings. Initial work on the integration of thin sensors in bearings can be found, for example, in Konopka et al [36][37][38].…”