Page 124 - Handbook of Adhesives and Sealants

Chapter
3

Joint Design

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 ex-
tremes.
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 ad-
hesives or sealants can lead to unfavorable results.
As with most fundamental processes involving adhesives or seal-
ants, joint design cannot be completed without consideration of nu-
merous 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 require-
ments 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 ori-
entation to the joint.
This chapter will define the types of stress that are common to ad-
hesive and sealant joints. The reason why shear stress is preferred
over peel or cleavage stress will be made clear. Various designs will
be recommended for several common joint geometries. Stress distri-
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