INTRODUCTION
Adhesives are substances capable of holding materials together in a useful manner by surface attachment. The principal attribute of adhesives is their ability to form strong bonds with the surfaces of a wide range of materials and to retain bond strength under expected use conditions. Most adhesives do not have excellent bulk properties; therefore, it is important to keep adhesive films thin. Some materials, such as epoxies, have bulk properties that qualify them as engineering materials and thus can be used in multifunctional applications. Adhesive is a general term and includes among others cement, glue, mucilage, and paste. All of these terms are loosely used interchangeably.
The principal advantages of adhesives are listed below:

Ability to bond similar to dissimilar materials of different thickness Enable the fabrication of complex shapes not feasible by other fastening means Smooth external joint surfaces Permit economic and rapid assembly Distribute stresses uniformly cover joined interfaces Provide weight reduction in critical structures via the elimination of fasteners Dampen vibrations Prevent or reduce galvanic corrosion
• Provide thermal and electrical insulation