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Unformatted text preview: SURFACE PREPARATIONS FOR ENSURING THAT THE GLUE WILL STICK IN BONDED COMPOSITE STRUCTURES 29 L.J. Hart-Smith, D. Brown and S. Wong 29.1 INTRODUCTION Adhesively bonded joints can be no stronger than the interface between the adhesive and the members being bonded together. In-ser- vice bond failures have always been associated with weak interfaces, for both metal and composite adherends. While most people acknowledge that adhesive bonding of metal- lic structures requires strict adherence to proper processes, many people unthinkingly accept the notion that it is easy to make epoxy stick to epoxy, for example, and pay no atten- tion to the need for proper processing for the adhesive bonding of composite structures. This chapter begins with a historical review of the need for appropriate surface treatment to ensure that the glue will stick to composite sur- faces. It then focuses on photomicrographs of different surfaces, to which the adhesive will or will not stick, as a basis for inspections prior to bonding. Such prebond inspections are vital because of the inability to detect weak bonds after manufacture, until they have fallen apart. The characterization of the surfaces prepared by different techniques can assist in formulat- ing process specifications that will ensure reliable adhesive bonding and in identifying past practices that should be discontinued. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 29.2 HISTORICAL BACKGROUND During the late 1970s and early 1980s, the Douglas Aircraft Company at Long Beach, California, was the site of one of the techni- cally most successful research contracts ever funded by the Wright-Patterson Air Force Laboratories - the Primary Adhesively Bonded Structure Technology (PABST) pro- gram. This research was directed at well-known problems concerning the adhe- sive bonding of metallic aircraft structures. These problems were the need to change con- temporary processing from etching to anodizing, and the need to select adhesives and primers on the basis of long-term dura- bility rather than short-term strength. These failings had been made very clear by wide- spread in-service problems experienced for many years by both commercial and military operators. A successful outcome to the research was assured because of the success of the Redux bonding developed in England during WWII and since employed exten- sively by Fokker. The PABST program succeeded in all of its objectives, bar one. It omitted a large-scale flight demonstration program, because it would have solved no problem that had not already been solved by the successful ground testing of panels and a complete wide-body fuselage barrel with simulated wing center section. However, in 668 Suface preparations for ensuring that the glue will stick in bonded composite structures retrospect, such a demonstration was neces- sary as a public relations exercise to convince the decision makers to apply the technology,...
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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