Finite Element Simulation To The Effect Of Acoustic Spectral Feature By Defects In Homogeneous Media

The modern nondestructive testing technologies (NDT) are developed towards the direction of high precision and accuracy. The numerical simulation have been more and more applied to the research of ultrasonic nondestructive testing because of the traditional theory and test method cannot meet the requirements of NDT development. It is generally believed that we can obtain limited flaw information in time domain. Hence, the spectrum analysis method which has been developed with the digital signal processing technology is used widely in NDT to obtain more features of flaws.In this paper, two-dimensional NDT models have been developed by finite element method. Firstly, the model which has three different size defects: crack, traverse square cavity and traverse cylindrical cavity is studied by simulation, we can obtain the different amplitude by the echo and transmission signal, and we can obtain the different characteristics in frequency domain, such as: peak, peak frequency, center frequency, bandwidth, half high width, quarter high width and sensitivity frequency etc; aiming at the transmission signal of traverse cylindrical cavity, variation laws of frequency characteristics can be obtained from spectrum analysis. Secondly, studying the model of planar and arc groove, we can obtain the different amplitude of the back wall echo and transmission signal, and we can obtain the characteristics in frequency domain and the sensitivity frequency; variation laws of planar groove in frequency domain can be obtained from the spectrum analysis of transmission signal also. Finally, the finite element models with metal and nonmetal inclusions are developed in steel to study the ultrasonic propagation; the results are proved to be correct and reliable by analysis of echo phase, and we can obtain the characteristics in frequency domain and the sensitivity frequency of all inclusions.The results can recognize defects and proved the correctness of finite element method and spectrum analysis technology in this paper. The simulation results may be useful to theory and test study, and offer a new idea for NDT.