Page 188 - Handbook of Adhesives and Sealants

158 Chapter Four

Figure 4.14 Cleavage test specimen. [From ASTM D
1062]

cycle line is usually reported as the fatigue strength. Fatigue strength
is dependent on adhesive, curing conditions, joint geometry, mode of
stressing, magnitude of stress, and frequency and amplitude of load
cycling.
Lap shear fatigue data are limited in engineering design because of
the stress distribution patterns of the lap shear specimen configura-
tion relative to practical joint designs. However, fatigue testing of the
actual part or of the joint itself provides useful engineering design
values.

4.4.6 Impact tests
Impact testing is of importance because adhesives, like most polymeric
materials, are sensitive to high rates of applied force. The resistance
of an adhesive to impact can be determined by ASTM D 950. This test
is analogous to the Izod impact test method used for impact studies
on materials.
The specimen is mounted in a grip shown in Fig. 4.15 and placed
in a standard impact machine. One adherend is struck with a pen-
dulum hammer traveling at 11 ft/s, and the energy of impact is re-
ported in pounds per square inch of bonded area. It is often difficult
to achieve reproducible results with impact testing, and as a result,
the test is not widely used in production situations. Impact data in-
dicate that as the thickness of the adhesive film increases, its appar-