科研之友
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摘要
As one of the most common fatigue damage, the detection of the closed crack using regular ultrasonic technique always failed because of the contact state of its interface. Nonlinear ultrasonic method had been employed to improve the detecting precision. The electromagnetic acoustic method based on high pulse stimulation is studied in this paper. In order to get the accuracy information, a closed crack model based on the modified virtual spring function is proposed. The finite element (FE) model of the electromagnetic ultrasonic propagation in the aluminium plate with closed crack was developed, followed by a look at the simulation results and analysis. An experimental setting which is coincident with the FE model is set up. By comparing of the simulation and experimental results, it is concluded that the tension and compression of the crack will cause the sound wave distortion and the ultrasonic nonlinear effect will be produced. The second harmonics is the typical feature of the nonlinearity. The propagation characteristic of surface wave in aluminium plate containing a closed crack is further analysed, which lays a foundation for the nonlinear detection of closed cracks.
