Investigations of Fatigue Crack Detection Using Local Vibration Techniques: Numerical and Experimental Studies

The Fatigue crack represents one of the most likely reasons for metal structural failures. It is crucial to detect it effectively to avoid a disastrous tragedy. This paper presented a developed procedure to assess the structural integrity and identify the fatigue crack using local vibration techniques. The process includes building computational modeling and conducting experimental investigations to detect and visualize the interesting fatigue crack. The finite-element modal analysis was performed to predict the resonance frequencies which cause high local vibration over the damage domain and extract corresponding mode shapes. These numerical results were validated by conducting electromechanical impedance spectroscopy (EMIS) and the scanning laser Doppler vibrometer (SLDV) experiments based on a developed method. The electromechanical impedance spectroscopy experiment was implemented to predict the crack resonance frequencies by measuring the electro-mechanical impedance of the bonded piezoelectric wafer active sensor (PWAS). Based on the developed method, the bonded PWAS was used to excite the test plate at a high frequency utilizing a linear sine wave chirp from 1 to 500 kHz. The SLDV was used to acquire the dynamic response of each scanning area point. The crack resonance frequencies and corresponding operational vibration shapes were extracted from SLDV measurements to detect and visualize the interesting fatigue crack. The result showed the frequency spectrum of SLDV measurements and corresponding operation vibration shapes have much information about the tested crack compared with the E/M impedance spectrum. Gathering the experimental and finite element modeling results shows good potential for accurately assessing structural damage.