Acoustic Emission testing

Magnetic acoustic emission testing of ferromagnetic material

Update time：2007-03-03 14:56　　　 Viewed：次

Electromagnetic acoustic emission technology is a new type of nondestructive testing technology. It generates acoustic emission by electromagnetic loading to possess the advantages of electromagnetic loading and acoustic emission testing, particularly suitable for nondestructive testing of conductive thin plate structure. Based on the theory of electromagnetic acoustic emission, this article makes research on the phenomenon of producing mechanical wave in the detect because of stress produced by applying electromagnetic field, so as to reveal the mechanism of the electromagnetic acoustic emission. Here we applying after transient electromagnetic field produced by a local dynamic stress with the defects of sheet metal was studied, and reveal the local applying electromagnetic acoustic emission phenomenon of power, and electromagnetic field can stimulate defect itself elastic mechanical wave used in nondestructive testing.

It is already a mature technology that produced by electromagnetic induction induced eddy current in the conductor material ultrasonic NDT. But it is a new concept to motivate acoustic emission by electromagnetic loading in conductor material. As we know, it will produce current concentration effect through the metal conductor of electric current in the conductor of defects (porosity, crack, or impurities) parts, as shown in figure 1. In the conductor defect parts by large density current to impose an electromagnetic force will be on the surface defects. In addition we see defect on either side of the tip of the current in the opposite direction, like a single turn solenoid coil, the magnetic flux concentrated and lorentz force. The defect tip current density can be an order of magnitude larger than the rest of the current density, to a certain extent as long as the tip of the current density will inspire more acoustic response can be obtained. It can be used to test the conductive plate defects.

Electromagnetic load of stimulating the acoustic emission can be the form of dynamic electromagnetic field induced eddy current, or directly electrify to the object to be measured. Dynamic electromagnetic induction eddy current load produce acoustic emission, through which nondestructive flaw detection without contact can be done. But for components that eddy current load coil is not easy to reach, it is more simple and feasible to use direct power flow method.

It is feasible to conduct nondestructive testing by electromagnetic acoustic emission, which is a very promising new technique in nondestructive testing. Defect itself is the characteristics of detection signal’s source, which make it have incomparable advantage in nondestructive testing of thin plate structure . We believe that electromagnetic acoustic emission technology will be an effective new nondestructive testing method with the further study of the electromagnetic acoustic emission technology.
(Editor：admin)

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