High-speed Acquisition And Analysis Of Electromagnetic Ultrasonic Signals From Ferromagnetic Materials

Metal materials with high strength,high temperature resistant and easy for manufacture characteristics,therefore,in the aerospace,railway,electricity and other fields is widely used.Metal workpiece in bad working conditions or high strength working condition,the weak position is easy to form active crack,High strength material active crack(it can generate elastic wave under working load)is easy to cause the metal workpiece suddenly rupture caused by equipment failure and even catastrophic accidents.So it is necessary to test the crack,determine the activity of the crack and to rate the level of fatigue damage in the crack.Electromagnetic Acoustic Transducer(EMAT)is widely used in nondestructive testing and evaluation for the characteristic of non-contact detection and to excite a variety of types ultrasonic,but how to use it to determine micro-crack activity has not been extensive research.Electromagnetically Induced Acoustic Emission(EMAE)can be used to detect the microcrack activity.In this paper,according to electromagnetically induced acoustic emission with eddy current exciting,combines with the principle of EMAT,applies EMAT in the electromagnetic acoustic emission detection method is put forward.In this paper,first of all,on the basis of considering the effect of magnetostriction,phenomenological constitutive model of magnetostrictive is established.Finite element analysis model of metal crack electromagnetic acoustic emission of surface wave EMAT.Analysis of the electromagnetic field-force-displacement field multi-physics coupling mechanism.Secondly,constructed with output excitation signal,data acquisition,signal processing,data storage,and other functions in the integration of virtual instrument,combining with the EMAT and electromagnetic loading equipment set up complete experimental system.Finally,according to the system complete the electromagnetic acoustic emission experiment,Acoustic emission signal is collected,the Wavelet Method and Fast Fourier Transform(FFT)are used to analyze signals,acoustic emission signal features are extracted.As shown the simulation and experimental results,under Lorentz force and magnetostriction stress work together,crack tip will cause stress concentration phenomenon in samples of 45#steel sheet,with the increase of exciting current,the force increase yield and make crack high frequency vibration,With the rapid release of internal energy,release the acoustic emission signal at moment.Get the acoustic emission signal strength changing with the exciting current amplitude and acoustic emission signal in the frequency range for roughly 200～300 kHz,based on AE Theory,Kaiser effect and fracture mechanics,This study provides a way to complete a composite detection method using EMAE and EMAT.The theory and application value clear...