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Eddy Current NDT and Deep Flaws (T.E.A.M. Problem 27)

Sensors and NDT with MagNet for SOLIDWORKS

In this example, a sheet of aluminum contains a screw hole with a flaw inside. The flaw is to be detected using the eddy current method. A coil is stationary above the screw hole, which generates eddy currents inside of the aluminum. Two diametrically opposed Hall effect sensors measure the horizontal differential flux density at the surface of the screw hole.

The current in the coil is generated using a step waveform. Once the current is shut off, the horizontal flux densities at either end of the screw hole are differenced.

The purpose of the experiment is to be able to optimize the dimensions of the coil and the excitation current to have the highest level of the signal as possible.

The following example is based on the Testing Electromagnetic Analysis Methods (T.E.A.M.) problem #27: Eddy Current NDT and Deep Flaws. The benchmark can be found on the International Compumag Society's website.

Cross-Section of an Aluminum Plate with a Flaw, and a Coil Acting as a Sensor



By displaying the mesh within components, MagNet for SOLIDWORKS allows users to see which areas of the model may need a more refined mesh.

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Shown here is the current density (J field) at four different time steps: 0.035s (current shut off), 0.0351s, 0.0352s, and 0.0355s. At 0.0352s, the peak horizontal differential flux density occurs.

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Shown here is the flux density at two different time steps: 0.035s and 0.0352s. The field distortion produced by the flaw can be seen in this plot.

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The small element size in the mesh control part allows probing the flux density field at a high density. This improves the smoothness and accuracy of the results. The results for the first coil position at the two driving frequency is presented in this graph. The same probing was used for every graph presented here.

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