Abstract:
A portion of the nondestructive evaluation (NDE) research being performed today is directed towards the inspection and characterization of advanced composite materials. Although ceramic and metal-matrix composites are being considered to date, much of this work has been with an emphasis upon graphite-epoxy systems. These materials, which are becoming increasingly popular due to their high specific strength and stiffness, do not readily lend themselves to the more established NDE methods which have been so successfully applied to their metallic counterparts. The problem becomes more pronounced as the number of fiber layers (plies) is increased; a necessity, nonetheless if the benefits of composite materials are to ever be realized in more sophisticated structures other than thin plates and shells.
One approach which appears especially well suited for NDE of composite structures is the acousto-ultrasonic (AU) method. This technique, made prominent by Vary, et al.', was selected by engineers at Olin Corp. for development into a production NDE system currently used to assess the quality of a particular composite part. The part has an irregular outer geometry, is composed of several hundred plies, and exploits a novel radial ply architecture as opposed to the more traditional circumferential lay-up. The AU system, as configured, utilizes a series of waveform signals collected via a multiple through-transmission probe arrangement. Digital signal processing and pattern recogmtion mathematics are then employed to ultimately yield an unambiguous go/nogo decision as to part integrity just prior to the final machining operations, the most cost intensive phase of production.
This paper is a follow-up to work that was presented in 1993 on the prototype Olin AU systems and describes the progress that has been made in the configuration of the platform. Modifications to the original system are presented, as are the results of over 10,000 test cycles in discerning various process-induced defects. Finally, the practical considerations of implementing AU in a high volume production environment are discussed.
Source: Proceedings of the 'NDE applied to Process Control of Composite Fabrication' - Conference, 4-5 Oct 1994 St. Louis, Missouri. Publisher and Organizer: Nondestructive Testing Information Analysis Center (NTIAC) Texas Research Institute Austin, Inc. Austin, Texas [http://www.ntiac.com] [Buying the Proceedings]
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