| In modern industrial production,metal components are widely used in all kinds of production equipment.Along with the manufacture,processing and use of metal components,it is inevitable to from micro cracks on the surface or inside.At the same time,under the influence of long term load,temperature change and corrosive medium,the micro crack of metal component will be enlarged,which will result in the fracture of metal component,which will cause great damage and loss to the production.Therefore,it is urgent to detect the micro cracks of metal components.Traditional methods of ultrasonic testing are using acoustic reflection,scattering and other linear features to detect the damage of materials.Due to its principle,it is not sensitive to the detection of metal micro cracks.According to the latest research,it is found that the internal stress,fatigue and micro cracks are closely related to the nonlinear effects of ultrasonic transmission through the material.Therefore,nonlinear ultrasonic testing has been widely concerned in the nondestructive testing of materials.However,the development of nonlinear ultrasonic detection system is not perfect,so this paper will design a complete set of nonlinear ultrasonic testing system,which includes the following:1.The nonlinear ultrasonic response is analyzed,and the principle of harmonic generation in nonlinear ultrasound is described.Then,from the nonlinear wave equation,the two order nonlinear coefficient.2.According to the relevant knowledge of nonlinear ultrasound,a suitable nonlinear ultrasonic testing method is chosen,and a set of nonlinear ultrasonic testing scheme is designed.3.A reasonable signal conditioning circuit is designed to preprocess the received signal of the ultrasonic transducer.At the same time,a set of signal acquisition system based on FPGA is designed.4.By means of the nonlinear ultrasonic test on the aluminum sample,the results are processed and analyzed to verify the accuracy of the nonlinear ultrasonic testing system. |
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