Page 186 - Handbook of Adhesives and Sealants

156 Chapter Four

Figure 4.12 Equation for peel force required to strip a flexible adherend from a rigid
substrate. 8

4.4.4 Cleavage test
Cleavage tests are conducted by prying apart one end of a rigid bonded
joint and measuring the load necessary to cause rupture. Cleavage
tests are used in place of peel tests when both adherends are rigid.
The test is also a qualitative measure of the fracture toughness of the
adhesive. Data obtained are adaptable to engineering design.
The cleavage test utilizes a specimen similar to a compressive shear
specimen except that the load is intentionally placed on one edge of
the bonded area. The test method is described in ASTM D 1062. The
specimen is usually loaded at a rate of 0.05 in/min until failure occurs.
The failing load is reported as breaking load per unit area in psi units.
A standard test specimen is illustrated in Fig. 4.14. Because cleavage
test specimens involve considerable machining, peel tests are usually
preferred where possible.