Experimental detection of additional harmonics due to wear in journal bearings using excitation from a magnetic bearing

An experimental rotor bearing system with an elastic rotor mounted in worn journal bearings is designed and investigated. The system is operated at run-up and run-down conditions and the response is analyzed with emphasis on passage through the first critical speed. Wear introduces additional sub- and super-harmonics in the response signal compared to the intact system. Time histories are analyzed in the time–frequency domain and bispectrum analysis is also performed in order to extract information on the influence of wear depth to these additional harmonics. Wear in one journal bearing is artificially produced and two cases of wear depth are investigated, one of 20% of bearing radial clearance and one of 40%.