Internal friction and loss tangent of nonlinear viscoelastic materials: different concepts, different results

This paper deals with the application of three advanced spectral methods aimed to be used for detection/diagnosis of localized defects in rolling element bearings. Second order power spectral density proves to be useful as a tool for peak identification and an aid to classical linear spectra. Bispectral techniques show its effectiveness in quadratic phase coupling peak detection, and because its a third order moment function noise background is eliminated in the estimation procedure, being capable of detecting them. Wavelet analysis using a simplified technique via Haar transform proves to be applicable in early detection of the burst generated during a fault development. Results are presented based on a digital simulation model.