Page 149 - Handbook of Adhesives and Sealants

118 Chapter Three

will go into tension. The movement of a sealant in a butt joint is shown
in Fig. 3.22.
Early investigators used dog-bone tensile specimens of the cured
sealant itself to determine elongation capacity and tensile strength;
however, these results do not compare with the behavior of the sealant
in actual joints. Peterson 12 showed that this was the result of unequal
stress distribution. Figure 3.23 shows the concentration of stress in a
butt joint at the corners.

3.6.1.1 Elastic sealants. Elastic sealant materials are prime candi-
dates for working joints because they return to their original shape
after the removal of the imposed force. This property of recovery is
desirable for sealants that must have a 25% joint movement capa-
bility.
When large movement capabilities are required, joints with shallow
depth are the best design for reducing strain. It is not possible to

Figure 3.22 Movement of sealant in a butt joint. 13

Figure 3.23 Unequal stress distributions in sealant butt joints. 13