3.1 Introduction

The strength of an adhesive or sealant joint in the absence of outside or environmental factors is determined by the mechanical properties of the materials comprising the joint, the extent of interfacial contact, and residual stresses within the joint. To design a practical joint, it is also essential to know as much as possible about the expected service requirements including anticipated stresses and environmental extremes.

The design of the adhesive or sealant joint will play a significant factor in determining how it will survive outside loads. Although it may be tempting to use joints originally intended for other methods of fastening, adhesives and sealants require joints of a special design for optimum properties. The practice of using joints designed for some other method of assembly and slightly altering them to adapt to adhesives or sealants can lead to unfavorable results.

As with most fundamental processes involving adhesives or sealants, joint design cannot be completed without consideration of numerous other factors. One must have familiarity with the adhesive or sealant materials, their physical properties, and the cure conditions that will be employed. One must also be familiar with the requirements and costs of machining and forming substrates into various joint geometries. Finally, one must be cognizant of the types of stresses anticipated in service, their magnitude and duration, and their orientation to the joint.

This chapter will define the types of stress that are common to adhesive and sealant joints. The reason why shear stress is preferred over peel...