© 2006 by Taylor & Francis Group, LLC

126 Corrosion Control Through Organic Coatings
7.3.3 STRESSING THE ACHILLES’ HEEL
Every coating has its own Achilles’ heel — that is, a point of weakness. The ideal
test would accelerate all stresses to the same extent. It would then be possible to
compare coatings with different aging mechanisms — different Achilles’ heels —
to each other.
Unfortunately, it is not possible to accentuate all stresses evenly. Furthermore,
it is not possible to accentuate all weathering factors and still maintain the balance
between them that exists in the field. When we increase the percentage of time with
UV load, for example, we change the ratio of light and dark and move a step away
from the real diurnal cycle seen in the field.
Because it is not possible to evenly accelerate all aging factors, the best testing
tries to imitate an expected failure mechanism. Each test accentuates one or a few
stresses that are rate-controlling for a mechanism. By choosing the right test, it is
possible to thus probe for certain expected weaknesses in the coating/substrate
system. The trick, of course, is to correctly estimate the failure mechanism for a
particular application, and thus pick the most suitable test.
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© 2006 by Taylor & Francis Group, LLC