Design Rules and Methods to Improve Joint Strength

Abstract

One of the main reasons for the increasing use of adhesive bonding is the fact that the stress distribution is more uniform than with other conventional methods of joining which enables to reduce weight. However, even in adhesive joints the stress distribution is not perfectly uniform and this leaves room for improvements. The major enemy of adhesive joints is peel or cleavage stresses. These should be reduced if strong joints are to be designed. In this chapter, the main factors influencing the joint strength are first discussed. The focus is on lap joints because these are the most common. Methods are then proposed to improve the joint strength by using fillets, adherend profiling, and other geometric solutions. Hybrid joining is also a possibility to improve the strength of adhesive joints, and adhesives may be used in conjunction with rivet or bolts, for example. Joints may be damaged in some way and it is important to discuss also methods to guarantee an efficient repair design. Finally, configurations are recommended for several types of joints such as butt joints, strap joints, cylindrical joints, and T joints. The main rule for all cases is to spread the load over a large area and reduce the peel stresses.