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18 June 2002 Investigation of delaminations with ultrasonic spectroscopy
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In a previous study by the authors, the ultrasonic spectroscopy technique identified possible disbonds or delaminations that went unsubstantiated by other NDE (nondestructive evaluation) methods. The specimens were polymer matrix composite (PMC) rings sectioned from flywheel rotors. For this study, polymer matrix composite (PMC) rings were further investigated to determine the sensitivity of the ultrasonic spectroscopy technique in detecting tight disbonds or delaminations. The ultrasonic system utilizes a continuous swept sine waveform as the input. After the swept sine wave traverses the material, the captured waveform is subjected to two fast Fourier transforms (FFT); i.e. an FFT operation is performed on the amplitude versus frequency plot obtained by the first FFT. The second FFT along with equalization of the frequency spectrum allows for the evaluation of the fundamental resonant frequency as a function of material properties and thickness. Here, a study of ultrasonic spectroscopy's sensitivity to delaminations was conducted. Data was collected while opening a controlled delamination. The delamination opening was monitored using optical methods. The full thickness resonance, the resonance corresponding to the location of the intentional disbond, and the frequency spectrum were examined in an effort to characterize the sensitivity of the NDE method concerning various delamination conditions.
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Laura M. Harmon, Andrew L. Gyekenyesi, Richard E. Martin, and George Y. Baaklini "Investigation of delaminations with ultrasonic spectroscopy", Proc. SPIE 4704, Nondestructive Evaluation and Health Monitoring of Aerospace Materials and Civil Infrastructures, (18 June 2002);

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