Electricity: measuring and testing – Magnetic – Stress in material measurement
Patent
1995-06-05
1997-12-16
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Stress in material measurement
73799, 73810, 324225, 324240, 324242, 324262, G01N 2790, G01N 332, G01N 1908, G01R 3312
Patent
active
056989776
ABSTRACT:
Flux-focusing electromagnetic sensor using a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks and material loss in high conductivity material. A ferrous shield isolates a high-turn pick-up coil from an excitation coil. Use of the magnetic shield produces a null voltage output across the receiving coil in presence of an unflawed sample. Redistribution of the current flow in the sample caused by the presence of flaws, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal.
Maximum sensor output is obtained when positioned symmetrically above the crack. By obtaining position of maximum sensor output, it is possible to track the fault and locate the area surrounding its tip. Accuracy of tip location is enhanced by two unique features of the sensor; a very high signal-to-noise ratio of the probe's output resulting in an extremely smooth signal peak across the fault, and a rapidly decaying sensor output outside a small area surrounding the crack tip enabling the search region to be clearly defined. Under low frequency operation, material thinning due to corrosion causes incomplete shielding of the pick-up coil. Low frequency output voltage of the probe is therefore a direct indicator of thickness of the test sample.
Fatigue testing a conductive material is accomplished by applying load to the material, applying current to the sensor, scanning the material with the sensor, monitoring the sensor output signal, adjusting material load based on the sensor output signal of the sensor, and adjusting position of the sensor based on its output signal.
REFERENCES:
patent: 3918299 (1975-11-01), Donnadieu
patent: 4316146 (1982-02-01), Jilken
patent: 4689558 (1987-08-01), Ruuskanen et al.
patent: 4755753 (1988-07-01), Chern
patent: 5339031 (1994-08-01), Chern
patent: 5423223 (1995-06-01), Weinstock
Fulton James P.
Namkung Min
Nath Shridhar C.
Simpson John W.
Todhunter Ronald G.
Edwards Robin W.
Strecker Gerard R.
The United States of America as represented by the Administrator
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