In this paper, nonlinear identification of structures is attempted using Hilbert Huang Transform (HHT) and wavelet transform (WT) to extract the desired features for identification of the presence of nonlinearity. It is shown in this paper that the instantaneous frequency and Hilbert marginal spectrum obtained from HHT and holder exponent obtained from WT are good indicators of the presence of nonlinearity. A numerically simulated example and also an experimental data is analyzed to evaluate the robustness of these nonlinear indicators. In this paper, the investigations are carried out on a breathing crack problem which exhibits a bilinear stiffness effect and an eight degree of freedom spring mass system.

Keywords: Nonlinear systems, Hilbert huang transform, Wavelet transform.