Implementing Noise, Multi-Frequency Stimulus, and Realtime Analysis to Nonlinear Model Tracking

• Published in: Fracture, Fatigue, Failure and Damage Evolution, Volume 8 pp. 143 - 152
• Main Authors: Doughty, Timothy A., Cassidy, Liam J., Danforth, Shannon M.
• Format: Book Chapter
• Language: English
• Published: Switzerland River Publishers 2017; Springer International Publishing AG; Springer International Publishing
• Edition: 1
• Series: Conference Proceedings of the Society for Experimental Mechanics Series
• Subjects: Failure; Mechanical engineering; MECHANICAL ENGINEERING & MATERIALS; Modal; Nondestructive health monitoring; Nonlinear; Testing of materials; Vibrations; Vibrations; Nonlinear; Modal; Nondestructive health monitoring; Failure
• ISBN: 9783319825205; 9783319421940; 3319421948; 3319825208
• ISSN: 2191-5644; 2191-5652
• DOI: 10.1007/978-3-319-42195-7_20

Crack initiation in a cantilevered beam subject to harmonic excitation near the beam's second natural frequency has been determined using Nonlinear Model Tracking (NMT), a health monitoring technique. This method assumes a second order nonlinear differential equation model with cubic stiffness; the nonlinear parameter is tracked until catastrophic failure using a Continuous Time based System Identification. Previous research has shown that significant change in the value of the nonlinear parameter indicates the system's transition from healthy to unhealthy. This study introduced Gaussian noise into the raw stimulus and response data at various signal-to-noise ratios. The results were compared with those of the original data to highlight the technique's effectiveness in determining a change in the system's health. The model's robustness was also investigated by exciting the system at a range of frequencies near resonance, and the results of this test were compared to results from excitation at a single frequency. New methods of identifying crack formation in the beam were also implemented. The raw acceleration response data was plotted next to the nonlinear parameter in real time, and the system's natural frequency was recorded before and after crack initiation.