Original Date: 10/14/1988
Revision Date: 01/18/2007
Best Practice : Detection of Backing Material Inclusions
The inclusion of prepreg backing material in composite laminates is an industry wide problem. Backing inclusions are generally not detected until the material has been cured and is in final inspection. If the inclusion is large enough to cause rejection of the component, it results in a serious financial penalty.
Bell Helicopter Textron, Inc. (BHTI) has developed a manufacturing practice that effectively solves this problem. The solution is the use of an aluminum foil polyester/polyethylene backing material that is easily detectable with eddy current inspection equipment. The approach requires BHTI to replace the backing material normally supplied with prepreg broadgoods with the aluminized backing material. This material, which is designated BF-41707, is supplied by Bell Fibre Corporation, 918 Eighth Avenue, Columbus, GA Telephone: (404) 323-7316.
The aluminized backing material can be detected through up to 20 plies of graphite/epoxy laminates. The procedure requires the person laying up the laminate use a portable eddy current detector (such as the Hocking AV10B or NORTEC 23 models) on the lay-up before compaction. If an inclusion is found at this stage in the process, it can be easily removed. With the proper adjustments, the detector can be used on laminates that are being laid up on aluminum, steel, graphite, and other conductive tooling materials.
BHTI conducted a thorough evaluation of the new backing material with respect to cutting, cold storage, workability and other considerations. With only minor adjustments, the aluminized backing material has been fully adopted. Since the procedure is an in-process technique, certification is not required. An additional advantage of adopting this material is that it is less expensive than currently used backing materials.
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Point of Contact for this survey.