Early detection of damage to rolling bearings by electrical impedance measurement

• Applicant: Professor Dr.-Ing. Eckhard A. Kirchner
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 463357020

The aim of the project is to identify an impedance-based damage indicator for the early detection of rolling bearing damage. The advantage of such an early damage detection compared to a damage detection based on structure-borne sound is the earlier response of the damage indicator already in case of microscopic changes of the contact surface. Before surface damage occurs, the change in impedance can provide information about the impending initial damage.Test series with closely monitored impedance are carried out without the measurements themselves causing electrically induced damage. The use of available lifetime tests is not possible due to the lack of regular impedance measurements. A measuring method must be used which can differentiate between lubricant and aging influences and which operates at measuring voltages below the breakthrough voltage of the lubricant film.In order to interpret the measurements and to correlate them with changes in the rolling contact, the surface properties of the contact partners must be regularly examined in a non-destructive manner. With the determined roughness and the time series of the impedance characteristics, empirical prognosis approaches are developed on the basis of measurable damage indicators and correlated with changes in the surface of the rolling bearings. In addition, artificial intelligence methods are used in order to make forecasts based on a black box approach for an imminent failure if a sufficient amount of structured data is available and to compare these with the further test procedure.Based on preliminary tests, two fundamental research questions are analyzed within the work program, firstly for deep groove ball bearings of one size in a defined test program:RQ 1: Can characteristic changes in the impedance of a rolling bearing be demonstrated over the nominal life and can these be used as a damage indicator for imminent rolling bearing damage. Does the electrical impedance of the rolling bearing or an indicator derived from it show a characteristic curve as a function of the cumulative damage?RQ 2: Which phenomenological models explain the characteristic changes of the impedance or the derived statistical indicators?In order to investigate variant diversity and operating conditions in sample cases, further questions are investigated at the same operating temperature:FF 3: Are the impedance changes or the derived statistical indicators similar for different bearing types and load angles?FF 4: Does the running-in procedure influence the characteristic change of the impedance?FF 5: Is the characteristic change of the impedance independent of the size?The purely mechanical Fatigue behavior of rolling bearings is not investigated within the scope of this project. The load carrying capacity specified by the manufacturers is used to evaluate the change in impedance.

• DFG Programme: Research Grants