Method And Signal Processing For Ultrasonic Testing Of Multi-layered Adhesive Interface

Ultrasonic testing, one of the common nondestructive testing technologies, is widely used in aerospace, nuclear, petroleum industry and other fields for defects in the adhesive structure. It is difficult to detect interface debond in the adhesive multi-layered steel-rubber structure through the common ultrasonic testing due to the considerable acoustic impedance differences of between the steel and the rubber. The ultrasonic testing and signal processing for bonded defects in the structure of flexible joint of the solid rocket motors are studied. And the Lamb Wave method and the Longitudinal Wave method are used in the ultrasonic testing.The transmission rule of the lamb wave in the structure of the flexible joint is discussed, and the ultrasonic pulse echo is analyzed in the time-field and frequency-field. The Constant-separate method and the Adaptive-separate method based on the above ultrasonic principle are used to separate each interface-echo in the ultrasonic pulse echo. The feature of the each ultrasonic pulse echo is gained through the wavelet transformation, and is identified through BP neural network.The Longitudinal Wave method for testing the structure is also discussed. It is found that the bi-sensor method can determine whether the structure has interface debond. Then the adaptive filtering is adopted in the signal processing for the echo through single-sensor. Based on the above results, the feature of each interface echo is gained. It is shown by experiments that the Lamb Wave method and the Longitudinal Wave method are both capable of detecting the adhesive state of the structure. The detection of the structure becomes more comprehensive and effective if the above two methods ate employed in combination.