Nonlinear Model Tracking for varying system geometries

Abstract

Although linear models can successfully explain many behaviors for physical systems, they are unable to describe the complexities of nonlinear systems. Therefore, health monitoring methods based on linear models run the risk of misidentifying nonlinear behavior as failing. Nonlinear Model Tracking (NMT), a health monitoring technique, is used here on a slender cantilevered beam subject to harmonic excitation near the beams second natural frequency, and the fatigue due to excitation. A second order nonlinear differential equation model has been assumed with cubic stiffness. This method uses the Continuous Time based nonlinear system identification technique allowing for model parameter estimation based on stimulus and response. The robustness of this method is demonstrated in its implementation and application to differing system geometries. These geometries studied here illustrate the reliability of this methodology indifferent to the system under observation. This method has shown, with repeatability, the onset of crack initiation and growth, well in advance of catastrophic failure, and has also been shown to work when the healthy system behaves with distinct nonlinearities, where linear techniques fail. The results indicate that NMT can be used for many different systems. © The Society for Experimental Mechanics, Inc. 2013.