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Corrosion Detection in Airframes Using a New Flux-Focusing Eddy Current ProbeA new flux-focusing eddy current probe was recently developed at NASA Langley Research Center. The new probe is similar in design to a reflection type eddy current probe, but is unique in that it does not require the use of an impedance bridge for balancing. The device monitors the RMS output voltage of a pickup coil and, as a result, is easier to operate and interpret than traditional eddy current instruments. The unique design feature of the probe is a ferromagnetic cylinder, typically 1020 steel, which separates a concentrically positioned drive and pickup coil. The increased permeability of the steel causes the magnetic flux produced by the drive coil to be focused in a ring around the pickup coil. At high frequencies the eddy currents induced in both the sample and the cylinder allow little or no flux to link with the pickup coil. This results in a self-nulling condition which has been shown to be useful for the unambiguous detection of cracks in conducting materials. As the frequency is lowered the flux produced by the drive coil begins to link with the pickup coil causing an output which, among other things, is proportional to the thickness of the test specimen. This enables highly accurate measurements of the thickness of conducting materials and helps to facilitate the monitoring of thickness variations in a conducting structure such as an aircraft fuselage. Under ideal laboratory conditions the probe can sense thickness changes on the order of 1% as illustrated. However, this is highly dependent upon the thickness, and the geometric complexity of the sample being tested and for practical problems the sensitivity is usually much less. In this presentation we highlight some of the advantages and limitations in using the probe to inspect aircraft panels for corrosion and other types of material nonuniformities. In particular, we present preliminary results which illustrate the probes capabilities for detecting first and second layer corrosion in aircraft panels which may contain air gaps between the layers. Since the probe utilized eddy currents its corrosion detection capabilities are similar to convectional eddy current techniques, but the new probe is much easier to use.
Document ID
20040111964
Acquisition Source
Langley Research Center
Document Type
Other
Authors
Fulton, James P.
(Analytical Services and Materials, Inc. Hampton, VA, United States)
Wincheski, Buzz
(Analytical Services and Materials, Inc. Hampton, VA, United States)
Nath, Shridhar
(Analytical Services and Materials, Inc. Hampton, VA, United States)
Namkung, Min
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 1994
Subject Category
Instrumentation And Photography
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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