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2 INTRODUCTION The potential advantages of adhesive bonds relative to mechanical fastenings such as bolts and rivets are well known. For instance, in a current investigation by the U.S. Army of an all-composite airframe for a helicopter, it has been estimated that the use of adhesive bonding could save about 17 percent in airframe manufacturing costs and 22 percent in weight. Because of these advantages, the use of adhesive bonding for nonstructural applications in military and aerospace products has been growing during the past several years. Extensive experimental studies have been carried out on the structural use of adhesives, such as the U.S. Air Force PABST program. However, even though this program was quite successful, adhesive bonding of structural members has not been accepted by the U.S. military services for various reasons, including the degradation of properties of the adhesive joints under hot and/or wet conditions. Thus it appears that progress in establishing the reliability of adhesive bonds under severe conditions is the key to allowing the significant potential gains that may come from extensive structural use of adhesive bonds. It seems likely that the technology needed to overcome the remaining deterrents to the structural use of adhesives could be developed soon if appropriate efforts were directed to this objective. Therefore, at the request of the Department of Defense (DOD), the National Materials Advisory Board (NMAB) organized a workshop to establish the technological and scientific requirements for overcoming the limitations of adhesive joints under severe conditions. The organizing committee, listed on pages v and vi, defined the purpose and scope of the workshop, organized the agenda (see Appendix I), and developed the list of invitees. The response was excellent; the attendance list is shown in Appendix II. The proceedings of the workshop are summarized in the following chapters. The program started with a review of the needs of the DOD and of the National Aeronautics and Space Administration (NASA). Since the workshop was held immediately after a meeting on adhesion science at
Virginia Polytechnic Institute and State University (VPI), it was useful to review next the activities of that meeting (see Appendix III). Brief status reports were then presented for three important subtopicsâchemistry, interfaces, and mechanics. Further discussions on each of these subtopics were then carried out by three separate groups. The workshop finally reconvened in plenary session to discuss the findings of the three groups. It should be noted that, even though it was efficient to break down the subject into the three subtopics of chemistry, interfaces (interphases), and mechanics, in fact, adhesive joints must be treated as a system, and close interaction among the three subtopics is necessary to achieve optimum progress. In particular, close interworking between the experimentalists and the analysts is needed. Some topics were covered only slightly or not at all during the workshop. These include the effects of scrim on bond performance, flexible adhesives for textiles, and sensitivity to liquids other than water. These omissions were due to a combination of time constraints and interests of participants. It was agreed, however, that some of the omitted topics have considerable importance. An important topic not covered during the workshop is the bonding of elastomers to metals. The Navy has a massive problem with bond failure in sonar transducers, and bond failure has been identified as one of the causes of the Army's tank track pad problem. Another important topic not covered in the workshop is the severe effects expected with chemical decontaminants, in particular the highly corrosive DS2. The important topic of shelf life was deliberately omitted from consideration, since it was felt that it was dealt with adequately in the report of the NMAB Committee on Room-Temperature-Curing Resin Systems, which was published in March 1984. Finally, although composite-to-composite bonding was not explicitly stressed during the workshop, this in no way implied lack of recognition of the importance of this area of application. Its importance was evidenced, for instance, by references to the current Army development of an all- composite airframe for a helicopter.
