This data collection was more stringent than for the

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This data collection was more stringent than for the six-seat, propeller driven aircraft because of the vibration and noise from the engine just beneath the cowling. In both aircraft, the data were collected in flight, downloaded at the end of flight and processed later when specialized 365 Aerospace Applications of Acoustic Emission Testing F IGURE 6. Tail section of T-303 where the fatigue test object is inserted. F IGURE 7. Transducer placement and stress notch on test object.
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routines were evaluated for their efficacy in detection and classification. Processing of the digital waveform data (Fig. 10) involved various specialized routines and included time domain and frequency domain feature extraction. Figure 11 shows, for example, a simple one-dimensional wavelet transform of the acoustic event in Fig. 10. The multiresolution aspects of the wavelet transform produced a signature different from that of a fourier transform. In Fig. 11, the coefficients in the ranges from 512 to 1023, 256 to 511, 128 to 255, 64 to 127 and others provide information at different time-versus-frequency scales because of the localization of the wavelet transform simultaneously in time and space. This property of the wavelet transform offers interesting benefits when processing acoustic emission events. The wavelet basis function used for this example is a daubechies-4 mother wavelet, a highly localized basis function. Other representations can be used for acoustic emission event detection and classification. Training, test and validation data sets were built from the processed data and then applied to the neural network based detector and classifier. Results validated laboratory results. Good acoustic emission data have been collected from both aircraft and the processed data react as did the laboratory data when run through the detection and classification software. Conclusions Acoustic emission testing provides proven benefits to aviation. When properly applied, the method can isolate failures in real time and can locate cracks even when hidden by other structures or added equipment. Acoustic emission testing has been applied to the multipurpose fighter bomber and transport aircraft, both of which were difficult applications that could not be satisfied by other methods. Moreover, research results involving digital waveform processing for wideband acoustic emission testing offer complementary capabilities with narrowband transducers. The proven benefits of wide transducer spacing and high sensitivity of narrowband transducers can be combined with the automatic detection and classification demonstrated with wideband transducers. Acoustic emission test systems can blend automated detection, classification and location of failures as part of an integrated intelligent nondestructive test system in operational as well as maintenance applications.
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  • Fall '19
  • Fighter aircraft, Nondestructive testing, Acoustic Emission, Acoustic Emission Testing

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