Ultrasonic lamb wave second harmonic time domain signal measuring method based on group-velocity mismatch

Abstract

The invention provides an ultrasonic lamb wave second harmonic time domain signal measuring method based on group-velocity mismatch. When phase velocity of fundamental frequency matches phase velocity of frequency-doubled ultrasonic lamb wave and group-velocity is mismatched, a second harmonic signal generated in a fundamental frequency ultrasonic lamb wave propagation process can be fully separated from a second harmonic signal from a wedge ultrasonic transducer in time domain. According to propagation distance of ultrasonic lamb wave time domain pulse and group speed of frequency-doubled ultrasonic lamb wave, a time domain range of corresponding ultrasonic lamb wave second harmonic signal is determined. By adopting integration amplitude enveloped by second harmonic signal in the time domain range as characteristic parameter of measurement, second harmonic generation efficiency of the ultrasonic lamb wave is characterized. According to the invention, measuring condition of the ultrasonic lamb wave second harmonic signal is widened, and influence of the wedge ultrasonic transducer to the ultrasonic lamb wave second harmonic measurement can be fully deducted. The method of the invention can be used for accurate measurement of the ultrasonic lamb wave non-linear effect and lossless evaluation research of non-linear ultrasonic lamb wave of sheet materials.

Description

technical field [0001] The invention relates to the measurement technology of the nonlinear ultrasonic Lamb wave signal, especially the measurement method of the second harmonic wave time domain signal of the ultrasonic Lamb wave. Background technique [0002] In recent years, the research work on the nonlinear ultrasonic Lamb wave has attracted extensive attention of researchers. Existing research results show that the second harmonic signal that accompanies (fundamental frequency) ultrasonic Lamb wave propagation is closely related to the dispersion characteristics of Lamb wave and the nonlinear acoustic parameters of the plate or structure, so it can be used to characterize the plate Or the mechanical properties of the structure (such as the fatigue damage of the plate, etc.). However, due to the multi-mode and dispersion characteristics of Lamb wave, how to effectively and accurately measure the second harmonic signal of Lamb wave is a very complicated and difficult pro...

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Problems solved by technology

Therefore, the existing measurement methods are all based on the measurement under the condition that the fundamental frequency and double frequency Lamb wave phase velocity and group velocity match (see literature: 1. Bermes C, Kim JY, Qu JM and Jacobs LJ, Experimental Characterization of material nonlinearity using Lamb waves, Appl. Phys. Lett. 2007, 90(2), Art. No. 021901; 2. Pruell C, Kim JY, Qu JM and Jacobs LJ, Evaluation of plasticity driven material damage using Lamb waves, Appl. Phys. Lett. 2007, 91(23), Art. No. 231911; 3. Pruell C, Kim JY, Jacobs LJ and Qu JM, Evaluation of fatigue damage using nonlinear guided waves, Smart Mater. Struct. 2009, 18(03), Art. No. 035003; 4. Lee TH and Choi IH, The nonlinearity of guided wave in an elastic plate, Mod. Phys. Lett. B . 2008, 22(11), 1135-1140.), it has two deficiencies, one is that because the Lamb wave is dispersive, in general, when the condition of phase velocity matching is met, the condition of group velocity matching is not It must be satisfied, so the condition is too harsh; the second is that the group velocity matching will bring a problem, that is, the second harmonic response of the transducer and the second harmonic signal of the Lamb wave are completely overlapped in the time domain It is difficult to distinguish, which affects the accuracy of the measurement of ultrasonic Lamb wave nonlinear effect and affects its further application

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