Lamb Wave Disbond Detector

Under a university research grant from the Federal Aviation Administration, Penn State engineers have developed a new, hand-held, ultrasonic probe capable of detecting corrosion and delamination in layered fuselage structures. Dr. Joseph L. Rose, Paul Morrow Professor in Engineering Science and Mechanics at Penn State, leads the team that developed the probe. Rose recently demonstrated the probe on the Boeing 737 at the FAA Aging Aircraft Nondestructive Inspection Validation Center (AANC) during the Air Transport Association NDT Forum held on November 1-3 in Albuquerque, NM.

The Penn State device consists of two variable angle transducers, one at each end of a 12-inch double spring loaded handle. One transducer sends resonant sound waves into the plane's skin at special angles and frequencies while the other receives the waves in a pitch-catch approach. The spring loaded handle allows the two units to more effectively contact the curved surface of the aircraft fuselage. If there is good adhesion between the aircraft skins, the sound waves at certain resonances transfer efficiently from one skin to the other and can be detected by the receiver unit. If the adhesion is poor, as the result of corrosion, delamination, or other damage, the sound waves do not transfer. The Penn State device uses guided Lamb waves consisting of both longitudinal and transverse waves which have been shown to have greater sensitivity to the quality of the adhesive bond than longitudinal waves alone.

The device also showed promising results when tested on bonded composite repair patches and disbonded tear straps during a field test at the AANC during August 1994. Only slight variations in software and protocol are necessary to adapt the probe for use on other structures.

The probe is described in a series of publications including "Ultrasonic Guided Waves for NDE of Adhesively Bonded Joints in Aging Aircraft," Proceedings of Adhesion Society Meeting, Feb. 20-24, 1994, and "Lamb Waves for Aircraft Bond Inspection," Italian Journal of Non Destructive Testing, in press.

Guided wave probes for aircraft inspection based on this research will be available in early 1995 from Krautkramer Branson, 50 Industrial Park Road, Lewistown, PA 17044 (717) 242-0327 with system and software support from FBS, Inc., 141 W. Beaver Avenue, Suite 13, State College, PA 16801 (814) 234-6644. Other companies are also considering entering the aging aircraft inspection market with elements of this innovation. For additional information, contact Professor Joseph L. Rose at (814) 863-8026.

Information provided at NAARP NEWS

Sixth International Conference
on
Continued Airworthiness of
Aircraft Structures
 jointly sponsored by
The Federal Aviation
Administration
and
The National Aeronautics and Space
Administration
at the
Trump Taj Mahal Conference Facilities
Atlantic City, New Jersey
June 26-29, 1995
For further details contact:
Ms. Ingrid Miller
Mr. Dennis Flath
Galaxy Scientific Corporation
phone (609) 645-0900
FAX (609) 645-2881

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Rolf Diederichs 01. Aug 1996, info@ndt.net

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