The Mechanics of Bonding

The actual adhesive bond may be achieved in two ways:

• Mechanical: Here the adhesive penetrates into the surface and forms a mechanical lock, by keying into the surface. It also forms re-entrants, where the adhesive penetrates behind parts of the structure and becomes an integral part of the component to be joined.
• Chemical (Specific): In this method of bonding, the adhesive is spread over the surfaces to be joined and forms a chemical bond with the surface. In practice, most adhesives use both ways of bonding to form a joint.

Stresses on a Bonded Joint

Adhesive joints are liable to experience four main types of stress Joint stress is at a maximum when the adhesive is in shear (refer to figure below). Adhesives should not be used if significant stresses will be carried in tension or peel. Generally, lap joints are the types more favoured as the strength of the adhesive bond is proportional to the area bonded.

FIGURE