Research On Detecting Aluminum Material Cracks Based On Electromagnetic Acoustic Technology

Aluminum alloy,due to its characteristics of low density,high strength,high fracture toughness and strong corrosion resistance,is widely used in modern industries as well as in manufacturing aerospace equipment and military equipment.Defects detection of aluminum alloy in time and accuracy is necessary,not only because most applications requires high security,but also because of the inevitable production defects resulted from the materials manufactured and used.Regarding aluminum alloy plate,use cases of traditional ultrasonic testing technology is limited because of the need of coupling agent.While,electromagnetic ultrasonic testing technology not only has the advantages of traditional ultrasonic testing technology,but also is free from coupling agent.Thus,it can effectively detect aluminum alloy plate.This paper first targets the principle analysis and mathematical modeling of electromagnetic ultrasonic receiving and excitation.The electromagnetic ultrasonic process,which involves the electromagnetic field and force field,is complex.Thus,in this paper,the theory of ultrasonic wave in solid is analyzed,focusing on Lamb wave and Rayleigh wave,and the steps for drawing the dispersion curves of Lamb wave is provided.This paper also theoretically analyze Lorentz force-based EMAT and provided the weak form of coupling field equations in 2-D Cartesian coordinate system.Finally,the electromagnetic ultrasonic transducer is fabricated by the combination of back-type coils and permanent magnet.As the EMAT efficiency is low,a high-power excitation circuit and a good performance receiving circuit is required.In this paper,UCC3895 is selected as the control chip to drive MOSFET so that the power amplifier circuit generates high-power pulse signal.Use the AD620 as the amplifier chip,with the passive filter circuit to complete the weak signal amplification and conditioning.The multi-physics finite element analysis software COMSOL Multiphysics is used to simulate the EMAT excitation process.In the time domain simulation process,the results show that the Lamb wave can be successfully excited and propagated in the aluminum plate.A data acquisition system is developed by using Microsoft Visual Studio software based on C# language and an A/D acquisition card.The signal process software with functions such as signal acquisition,signal display,data storage,etc.Extensive experiments are conducted with appropriate data acquisition card.Lamb wave multi-modes in aluminum plate is verified using the self-developed electromagnet ultrasonic testing system.In order to avoid the bad effect of multi-modes and dispersion phenomenon,an appropriate frequencies-thickness,at which,the group velocities of different modes is consistent,is selected.