Frequency-Domain Characteristic Research On Ultrasonic Echo Of Bonding Quality Detecting Of Thin Plate

More and more thin composite materials have been applied in industry of aeronautics and astronautics for their superior performance. Disastrous accidents happen in process of working at times for bonding defect of composite material, so it is urgently needed to make accurate detection for bonding interface and insure the quality of products and working safety. Ultrasoni c echo method is widely applied in non-destructive detection for its advantage of accurate defect locating, wide application, convenient operation and so on.Usually defect in different property and size will reflect ultrasonic wave differently, and the echo is various. Some difference isn't evident in time domain even can't be extracted, therefore it is needed to make further research in frequency-domain. In the paper, the frequency-domain characteristic of ultrasonic echo of bonding quality detection for thin composite material has been researched. In study we mainly adopt the maximum entropy spectrum estimation and wavelet analysis to process the echo and extract characteristic quantity. In maximum entropy spectrum analysis the spectrum move method is applied to estimate the center frequency of echo, and the bonding quality is evaluated according to the skewingampl of center frequency. In wavelet analysis both time and frequency information of echo are researched. The echo is decomposed in multi-scale by db4 wavelet, and characteristic quantity is extracted in specific time-frequency area in where the energy distribution of echo is evidently different. By using the two methods a valid characteristic extraction way has been created used for bonding quality quantitative detection of thin composite material. It lays the foundation for the characteristic research of bonding quality quantitative detection of thin composite material and the design of dedicated digital ultrasonic detecting instrument.