Adhesives in land transport
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Adhesives in land
Many of the developments in structural adhesive bonding technology in the last three decades are attributable to the specific needs of the aerospace industry and the successful application of adhesives in aircraft construction provides a measure of the capabilities of bonding in critical assembly. The achievements of the adhesives manufacturers in collaboration with the aerospace industry and research establishments internationally have not gone unnoticed by other industries although, as with many other new technologies, the adoption of proven bonding methods in the more traditional engineering sectors has been relatively slow. The transport industry is no excep- tion. It is of course reasonable to argue that production quantities and manufacturing economics of land-based vehicles are several orders of magnitude different from aircraft production and expen- sive process technologies for surface pretreatment, adhesive application and curing cannot be applied in high-volume production. A further 'confidence-gap' has existed in the long-term durability and quality assurance of bonded structures.
However, in recent years a number of major influences have led to an expansion of interest in bonding technology in such diverse areas as bicycle construction, military vehicle production, corrP mercial Vehicle manufacture, car body assembly, automotive component sub-assembly and railway rolling-stock construction. The incentives for turning to adhesive bonding as a production joining process are varied but the primary factors may be divided into three distinct directions.
In nearly all forms of transport, vehicle weight reduction is a primary objective and this is lead- ing to the use of new materials such as foams, composites, composite/metal combinations, and light alloys which cannot be joined by the more conventional welding processes.
The recent developments in adhesive materials enable bonding techniques to be applied in pro- duction with a simple process technology. Many new adhesives are grease-tolerant, cure quickly at room temperature to give high-strength joints, and can be dispensed by robotics.
The technical advantages of bonded joints such as uniformity of loading, retention of surface smoothness, and fatigue resistance which are exploited in aerospace applications are equally desirable in general vehicle construction.
Many examples may be cited to illustrate developments and applications in each of these areas and part of this special issue is devoted to case studies and reports of 'adhesives in action'. Other papers deal with research into topics with a specific transport orientation and design philosophies in vehicle construction. It is hoped that this collection of articles will stimulate a greater awareness of the potential of adhesives in transport and provide a cross-fertilization of ideas across the many facets of the transport industries. It may also assist in forecasting the possible directions of bond- ing technology in the future.
Further 'sign-posts' from other sources might also help to lift the veil from the crystal ball to give a more accurate forecast of future trends. For example, double-sided pressure-sensitive tapes are already used in many applications for external attachment of lightweight components on vehi- cles and it is likely that recent developments in tape products will enable them to be used more extensively in semi-structural assembly. Hot melts are also progressing towards a capability for semi-structural metal-to-metal bonding, and a 1983 American forecast identified hot-melt technol- ogy as a significant growth area with the automotive industry as a major market
Techniques for the analysis of adhesive joints have been developed which provide a more pre- cise design tool for bonded structures. Finite element, continuum mechanics, and fracture mechanics methods are being researched and applied by many investigators internationally. A major project at AERE Harwell, UK, being funded by the European motor industry and adhesives manufacturers, is aimed at establishing analytical techniques, design methods and data for a variety of structures and materials in vehicle assembly. An empirical approach to structural performance evaluation has also provided an impressive demonstration of bonding capabilities in vehicle con- struction. Scandinavian developments with rigid PVC foam sandwich and bonded skin panels have led to a variety of structural applications in the production of railway rolling-stock. Very large monocoque refrigerated vans are now assembled by primary structural bonding of the edges of sandwich panels to form the corner joints of long box containers.
It can be seen therefore, that adhesive bonding technology is already playing a significant role in the construction of vehicles and recent developments in design methods, new adhesives, and improved techniques, coupled with the use of new materials will undoubtedly lead to an expansion of the use of adhesives in transport.
Mr. Beevers, Principal Lecturer in Production Engineering, Oxford Polytechnic, England. has acted as advisory and commissioning Editor for this Special Issue.
INT.J.ADHESION AND ADHESIVES JANUARY 1984 3