Adhesive Bonding

9–9 6 Adhesive Bonding

The use of polymeric adhesives to join components for structural, semistructural, and non- structural applications has expanded greatly in recent years as a result of the unique advan- tages adhesives may offer for certain assembly processes and the development of new adhesives with improved robustness and environmental acceptability. The increasing com- plexity of modern assembled structures and the diverse types of materials used have led to many joining applications that would not be possible with more conventional joining

6 For a more extensive discussion of this topic, see J. E. Shigley and C. R. Mischke, Mechanical Engineering Design, 6th ed., McGraw-Hill, New York, 2001, Sec. 9–11. This section was prepared with the assistance of

Professor David A. Dillard, Professor of Engineering Science and Mechanics and Director of the Center for Adhesive and Sealant Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, and with the encouragement and technical support of the Bonding Systems Division of 3M, Saint Paul, Minnesota.

484 Budynas−Nisbett: Shigley’s

III. Design of Mechanical

9. Welding, Bonding, and

© The McGraw−Hill

Mechanical Engineering

Elements

the Design of Permanent

Companies, 2008

Design, Eighth Edition

Joints

Welding, Bonding, and the Design of Permanent Joints

Windshield/

Hem Flange

Windows

15 Exterior Body Panels 1 8 1

2 Engine Interior

6 Paint Shop

9 Light Assemblies

5 Body-in-White

13 4 Wheel Housing

Brake/ Transmission

7 Exterior Trim 14 Sound Insulation

Figure 9–24

Diagram of an automobile body showing at least 15 locations at which adhesives and sealants could be used or are being used. Particular note should be made of the windshield (8), which is considered a load-bearing structure in modern automobiles and is adhesively bonded. Also attention should be paid to hem flange bonding (1), in which adhesives are used to bond and seal. Adhesives are used to bond friction surfaces in brakes and clutches (10). Antiflutter adhesive bonding (2) helps control deformation of hood and trunk lids under wind shear. Thread-sealing adhesives are used in engine applications (12). (From A. V. Pocius, Adhesion and Adhesives Technology, 2nd edition, Hanser Publishers, Munich, 2002. Reprinted by permission.)

techniques. Adhesives are also being used either in conjunction with or to replace mechan- ical fasteners and welds. Reduced weight, sealing capabilities, and reduced part count and assembly time, as well as improved fatigue and corrosion resistance, all combine to pro- vide the designer with opportunities for customized assembly. In 1998, for example, adhe- sives were a $20 billion industry with 24 trillion pounds of adhesives produced and sold. Figure 9–24 illustrates the numerous places where adhesives are used on a modern auto- mobile. Indeed, the fabrication of many modern vehicles, devices, and structures is depen- dent on adhesives.

In well-designed joints and with proper processing procedures, use of adhesives can result in significant reductions in weight. Eliminating mechanical fasteners eliminates the weight of the fasteners, and also may permit the use of thinner-gauge materials because stress concentrations associated with the holes are eliminated. The capability of polymeric adhesives to dissipate energy can significantly reduce noise, vibration, and harshness (NVH), crucial in modern automobile performance. Adhesives can be used to assemble heat-sensitive materials or components that might be damaged by drilling holes for mechanical fasteners. They can be used to join dissimilar materials or thin-gauge stock that cannot be joined through other means.