Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1994-11-22
1997-07-15
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324209, 324225, 324241, 324262, G01N 2790, G01R 3312
Patent
active
056487215
ABSTRACT:
A flux-focusing electromagnetic sensor which uses a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks about circular fasteners and other circular inhomogeneities in high conductivity material. The unique feature of the device is the ferrous shield isolating a high-turn pick-up coil from an excitation coil, The use of the magnetic shield is shown to produce a null voltage output across the receiving coil in the presence of an unflawed sample. A redistribution of the current flow in the sample caused by the presence of flaws, however, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal.
By rotating the probe in a path around a circular fastener such as a rivet while maintaining a constant distance between the probe and the center of a rivet, the signal due to current flow about the rivet can be held constant. Any further changes in the current distribution, such as due to a fatigue crack at the rivet joint, can be detected as an increase in the output voltage above that due to the flow about the rivet head.
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Fulton James P.
Namkung Min
Nath Shridhar C.
Simpson John W.
Wincheski Russell A.
Edwards Robin W.
Strecker Gerard R.
The United States of America as represented by the Administrator
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