Study Of Performance For Ultrasonic Nonlinear Testing System And The Method Of Signal Extraction

Composite is a new material, which has many excellent chemical properties, suchas wear resistance, high temperature resistance, good fatigue strength, not easy tocreep. These advantages of the conventional materials do not have made it widelyused in various fields. The RTM/textile composites is a composite componentobtained by RTM and the textile technology combined with high performance and lowcost. Due to external factors such as pressure, temperature, etc in the manufacturingprocess, RTM/textile composite materials easy to produce internal pore classmicroscopic defects. The existence of this kind of micro defects has decisive influenceon its service life.Based on the pore defects in RTM/textile composite, using nonlinear ultrasonictesting, build a nonlinear ultrasonic detection system, the system performance isanalyzed, study on the method of extracting harmonic signal, developed the filtersystem is used to improve the harmonic signal recognition.First of all, starting from the nonlinear wave equation in the ideal solid，discussedthe effect of nonlinear ultrasonic. Derive the second nonlinear coefficient and highorder nonlinear coefficient expression.Secondly, studied the nonlinear influence factors of the testing system,emphatically analyzed the performance of the nonlinear ultrasonic testing system ofthe parts. And take corresponding measures to increase the reliability of the materialnonlinearity coefficient measurement, such as choose excitation signal mode,optimizing the amplifier performance indicators, using high-quality transducer.Through the development of high and low pass filter and the operational amplifier toachieve the harmonic signal extraction.Finally, through the nonlinear ultrasonic testing RTM samples with differentcontent of the pore. Comparative studies on the influence of harmonic signalextraction by filtering system, through the trend analysis of nonlinear parametersverified the effectiveness and stability of the filtering system.The results of the study surface: Nonlinear ultrasonic testing system performancedirectly affects the reliability of the material nonlinearity coefficient measurement.Need in such aspects as transducer, acoustic coupling and signal processing to takecorresponding measures to inhibit or reduce the nonlinear influence of the system itself. In nonlinear acoustic measurement, the appropriate transducer does not fullysuppress the spurious frequency, correct design of the filter system can effectivelyrestrain the high power circuit is introduced into the nonlinear effects and transmittedpulse string of the own nonlinear interference, so as to realize extract the smallamplitude signals from large amplitude signal.