The Detection And Localization Imaging Based On Vibro-acoustic Modulation Of Metal Micro-crack

Metal materials will undergo micro-crack propagation before the macroscopic defect appears.Therefore,it is necessary to detect the micro-crack in time.Traditional linear ultrasonic detection is insensitive to micro-crack due to its limitations in principle.In recent years,it has been found that the vibro-acoustic modulation(VAM)can detect the micro-crack in the structure by the nonlinear modulation effect in the detection signals.Therefore,the mechanism of nonlinear effect by produced by micro-crack under VAM and the localization imaging of the micro-crack are studied in this paper.(1)The basic theory of VAM based on the classical nonlinear theory is introduced,and the one-dimensional wave equation based on contact nonlinear is obtained.The approximate solutions under different frequency excitations are solved and the nonlinear phenomenon of VAM is explained in principle.Then,the nonlinear phenomena caused by the interaction between micro-crack and acoustic wave are decried.Finally,the nonlinear spring model is established to explain the nonlinear modulation effect of micro-crack under the VAM from the microscopic,and the finite element modelling of the rectangular crack is carried out.(2)On the basis of finite element modelling of rectangular micro-crack,a three-dimensional finite element of aluminum plate is constructed.The vibro-acoustic modulation simulation is carried out,and the correctness of the model is verified by Kolmogorov entropy.The opening and closing states of micro-crack under different excitations and the propagation characteristics of mixed excitation acoustic wave in the aluminum are analyzed by finite element post-processing module.Finally,the main factors that affect the effect of VAM are discussed.(3)The micro-crack imaging approach based on vibro-acoustic modulation and time-and-sum imaging algorithm is presented.The localization imaging is performed by using nonlinear damage signals.And the effectiveness of the imaging method is verified by finite element simulation.(4)The VAM detection system is built and the vibro-acoustic modulation detection and imaging experiment of micro-crack in aluminum plate are carried out.As well as,the correctness of the nonlinear spring model is verified by experiment and the imaging of micro-crack on aluminum plate is realized.At last,the detection and localization imaging based on vibro-acoustic modulation are carried out on the sample of painted iron plate with engineering structure.