Nonlinear harmonic waves generated at cracked interfaces are investigated theoretically and experimentally.A compact tension specimen is fabricated and the amplitude of the transmitted wave is analyzed as a function o...Nonlinear harmonic waves generated at cracked interfaces are investigated theoretically and experimentally.A compact tension specimen is fabricated and the amplitude of the transmitted wave is analyzed as a function of position along the fatigued crack surface.In order to measure as many nonlinear harmonic components as possible,broadband lithium niobate(LiNbO3)transducers are employed together with a calibration technique for making absolute amplitude measurements with fluid−coupled receiving transducers.Cracked interfaces are shown to generate high acoustic nonlinearities,which are manifested as harmonics in the power spectrum of the received signal.The first subharmonic f/2 and the second harmonic 2f waves are found to be dominant nonlinear components for an incident toneburst signal of frequency f.To explain the observed nonlinear behavior,a partially closed crack is modeled by planar half interfaces that can account for crack parameters,such as crack opening displacement and crack surface conditions.The simulation results show reasonable agreement with the experimental results.展开更多
We present an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves.We first consider the flexural wave(A0 mode)propagation in a plate containi...We present an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves.We first consider the flexural wave(A0 mode)propagation in a plate containing a defect,and reception and time reversal process of the output signal at the receiver.The received output signal is then composed of two parts:a directly propagated wave and a scattered wave from the defect.The time reversal of these waves recovers the original input signal,and produces two additional sidebands that contain the time-of-flight information on the defect location.One of the side-band signals is then extracted as a pure defect signal.A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors.The simulation results show that the proposed scheme enables the accurate,baseline-free imaging of a defect.展开更多
This study concerns calculation of phased array beam fields of the nonlinear Rayleigh surface waves based on the integral solutions for a nonparaxial wave equation. Since the parabolic approximation model for describi...This study concerns calculation of phased array beam fields of the nonlinear Rayleigh surface waves based on the integral solutions for a nonparaxial wave equation. Since the parabolic approximation model for describing the nonlinear Rayleigh waves has certain limitations in modeling the sound beam fields of phased arrays, a more general model equation and integral forms of quasilinear solutions are introduced. Some features of steered and focused beam fields radiated from a linear phased array of the second harmonic Rayleigh wave are presented.展开更多
In nonlinear acoustic harmonic generation in solids with stress-free boundaries,such a boundary is known to destructively change the second harmonic generation,and the pulse-echo method is not practically applicable.F...In nonlinear acoustic harmonic generation in solids with stress-free boundaries,such a boundary is known to destructively change the second harmonic generation,and the pulse-echo method is not practically applicable.Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups.This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries.The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields.The phase difference between the two second-harmonic components after reflection from the boundary—that is,the reflected and the newly generated second harmonic—is emphasized.The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.展开更多
文摘Nonlinear harmonic waves generated at cracked interfaces are investigated theoretically and experimentally.A compact tension specimen is fabricated and the amplitude of the transmitted wave is analyzed as a function of position along the fatigued crack surface.In order to measure as many nonlinear harmonic components as possible,broadband lithium niobate(LiNbO3)transducers are employed together with a calibration technique for making absolute amplitude measurements with fluid−coupled receiving transducers.Cracked interfaces are shown to generate high acoustic nonlinearities,which are manifested as harmonics in the power spectrum of the received signal.The first subharmonic f/2 and the second harmonic 2f waves are found to be dominant nonlinear components for an incident toneburst signal of frequency f.To explain the observed nonlinear behavior,a partially closed crack is modeled by planar half interfaces that can account for crack parameters,such as crack opening displacement and crack surface conditions.The simulation results show reasonable agreement with the experimental results.
基金by Basic Science Research Programn(2010-0013901)by the Nuclear R&D program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology.
文摘We present an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves.We first consider the flexural wave(A0 mode)propagation in a plate containing a defect,and reception and time reversal process of the output signal at the receiver.The received output signal is then composed of two parts:a directly propagated wave and a scattered wave from the defect.The time reversal of these waves recovers the original input signal,and produces two additional sidebands that contain the time-of-flight information on the defect location.One of the side-band signals is then extracted as a pure defect signal.A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors.The simulation results show that the proposed scheme enables the accurate,baseline-free imaging of a defect.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61271356 and 51575541the National Research Foundation of Korea under Grant Nos 2013-M2A2A9043241 and 2013-R1A2A2A01016042the Hunan Provincial Innovation Foundation For Postgraduate under Grant No CX2016B046
文摘This study concerns calculation of phased array beam fields of the nonlinear Rayleigh surface waves based on the integral solutions for a nonparaxial wave equation. Since the parabolic approximation model for describing the nonlinear Rayleigh waves has certain limitations in modeling the sound beam fields of phased arrays, a more general model equation and integral forms of quasilinear solutions are introduced. Some features of steered and focused beam fields radiated from a linear phased array of the second harmonic Rayleigh wave are presented.
基金supported by the National Research Foundation of Korea(Grant No.2016M2A2A9A03913683)the National Natural Science Foundation of China(Grant No.51575541).
文摘In nonlinear acoustic harmonic generation in solids with stress-free boundaries,such a boundary is known to destructively change the second harmonic generation,and the pulse-echo method is not practically applicable.Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups.This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries.The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields.The phase difference between the two second-harmonic components after reflection from the boundary—that is,the reflected and the newly generated second harmonic—is emphasized.The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.
