Nondestructive Test Probe
Under NASA's Aircraft Structural Integrity program, which
addresses ways to enhance the safety of aging commercial jetliners
by improving structural inspection and lifetime prediction techniques,
Langley Research Center is developing a variety of devices and
procedures for detecting cracks, disbonds and corrosion during
routine aircraft service inspections. One such device is the
CrackFinder, now commercially available; it is manufactured by
Krautkramer Branson (KB Instruments), Lewistown, Pennsylvania
under an exclusive NASA license.
The CrackFinder is an electromagnetic probe for nondestructive
evaluation (NDE), developed to meet a need for a highly reliable,
low cost method of rapidly scanning aircraft skins for surface
breaks. It is based on eddy current technology that enables extreme
sensitivity to fatigue cracks in aluminum alloy plates. An eddy
current is an electrical current induced by an alternating magnetic
field; eddy current techniques are generally used for detecting
surface cracks, where ultrasonic systems are used for detecting
internal flaws.
Developed to scan aircraft skins for surface breaks, the CrackFinder
is available for industrial use in fatigue detection.
The device employs an innovative self-nulling feature that
makes the CrackFinder simple yet highly accurate, reliable and
economical. Self-nulling means that the device automatically
recalibrates to zero so that each flaw detected produces a reading.
When the probe is placed on a flaw-free metallic object, its
output is automatically nulled. The presence of a flaw alters
the delicate self-nulling condition, causing a distinctive probe
output amplitude. A bargraph display indicates crack severity.
A subsidiary of Emerson Electric Company, Krautkramer Branson
says the innovative probe removes some major limitations of conventional
eddy current testing: the CrackFinder is more affordable, costing
about one-third the price of a conventional eddy current instrument
package; it is small and lightweight, weighing only nine ounces
where conventional eddy current instruments weigh six to 20 pounds;
its small size and simplicity allow installation of multiple
probes in inaccessible locations for periodic monitoring of crack
growth in critical infrastructures; and it requires minimal operator
training. It also needs no calibration or balance circuitry.
The versatile CrackFinder has applications beyond the aging
aircraft market, for example, steel structures, ski lifts and
other structures where detection of fatigue is critical. NASA's
Technology Application Team at Research Triangle Institute played
a part in bringing the CrackFinder to market by identifying Krautkramer
Branson as a prospective NASA commercialization partner.
|
