Micro Crack Detection And Location Based On Vibro-acoustic Modulation Nonlinear Signal

Due to the restriction of principles,traditional linear ultrasonic testing method is unable to detect the closed crack.The nonlinear acoustic detection which is researched in recent years is sensitive to minor damages,however it can only evaluate the existence of crack,the size and location of crack is unable to know.In order to realize the detection and location of closed micro cracks,the research of micro crack detection basd on vibro-acoustic modulation(VAM)was studied in this paper,and the time reversal(TR)method was used to focus nonlinear signals.The major contributions including:(1)The background and significance of the topic were introduced,the research status of the related technical methods was summarized,and the structure and content of the paper were given.(2)The mechanism of the VAM was elaborated and the theoretical of the TR method was studied,the feasibility of the combination of VAM and TR method was deduced on the formula.(3)The VAM and TR method detecting micro crack in aluminum pipe was simulated by finite element software ABAQUS.It was proved that the TR mirror composed of a finite number signal sources can achieve the focus effect.And it could provide the reference for the parameter setting and TR mirror layouting in VAM experiment.(4)A VAM detection system was set up based on experimental scheme and used to performe VAM experiments on aluminum tube and plate which both contained micro cracks,the harmonic,sidebands etc were found in the detection signals.The effects on detection results of the amplitude and relative position of the excitation signal were analyzed.(5)Reversed the nonlinear signal in the time domain and loaded into the finite element model which was same material,size,structure with experimental specimen,then submitted simulation job,the crack can be located according to the distribution of the signals in the model.The results show that the nonlinear signals in the VAM detection signals will focus on the original crack position after time reversed and reloaded,the position error between focused image and crack is less than 5%,the precise localization of the micro crack is realized.