Damage Diagnostics of Composite Fan Blades Using the Modified Time Reversal Method

Abstract

This experimental study presents the Lamb wave based baseline-free diagnostics of damage in a carbon-fiber composite fan blade using the Modified Time Reversal Method (MTRM). A fan blade with delamination was selected as the test specimen and two piezoelectric transducers (PZT) were surface bonded using epoxy adhesive. The system (fan blade and transducers) was then waveform-tuned from which 5.5 cycle tone burst was selected as the optimum excitation waveform. The system was then mode-tuned in order to determine the optimum excitation center frequency. The 55 kHz, 5.5 cycle tone burst was used to generate fundamental asymmetric Lamb waves with high signal-to-noise ratio and low dispersion. Damage Index (DI) values for the fan blade was calculated at equidistant points on a line using both PZTs. Results show that magnitudes of the DI values have strong correlation with the severity of damage present in the fan blade. The procedure followed in this experimental study is directly applicable to the Non Destructive Evaluation (NDE) conducted on composite fan blades. Additionally, this method can be extended to develop a real-time structural health monitoring system for composite fan blades which employs embedded PZTs for actuating and sensing waves.