Factors that influence the adhesion - Stucture of the joint

An important prerequisite for the successful use of bonding technology is that the respective parts be suitably designed for bonding, as distinct from welding, for example.

Care must be taken to provide a sufficiently large bonded area, such as a large area of overlap of the mating parts. The ideal bonded joint is one under all practical loading conditions the adhesives is stessed in the direction in which it most resists failure. Favorable stress can be applied to the bond by using proper joint design.

Tensile shear stress
Butt joint = unfavourable	Simple butt joint = favourable
Bevelled joint = very favourable	Double-strap butt joint = favourable
Shouldered double-strap butt joint = favourable but labour-intensive	Double overlap = favourable

Bonded joints are particularly vulnerable to peeling stress and should therefore always be designed in such a way that the applied forces do not give rise to stress of this type.

Stress induced by shear forces
Pure peeling stress = unfavourable	Tensile peeling stress = very unfavourable
Transformation into tensile and compressive stress = favourable	Transformation into tensile shear stress = favourable
Combined rolling and peeling stress = very unfavourable	Transformation into tensile and compressive stress = favourable
Reinforcement = favourable

However, some joint designs may be impractical, extensive to make, or hard to align. The design engineer will often have to weigh these factors against optimum adhesive performance.